The Full Wiki

Nutrition: Wikis
  
  
  
  

Did you know ...


More interesting facts on Nutrition

Include this on your site/blog:

Encyclopedia

Updated live from Wikipedia, last check: June 04, 2012 04:34 UTC (50 seconds ago)

From Wikipedia, the free encyclopedia

The "Nutrition Facts" table indicates the amounts of nutrients which experts recommend you limit or consume in adequate amounts.
Nutrition (also called nourishment or aliment) is the provision, to cells and organisms, of the materials necessary (in the form of food) to support life. Many common health problems can be prevented or alleviated with a healthy diet.
The diet of an organism is what it eats, and is largely determined by the perceived palatability of foods. Dietitians are health professionals who specialize in human nutrition, meal planning, economics, and preparation. .They are trained to provide safe, evidence-based dietary advice and management to individuals (in health and disease), as well as to institutions.^ The information provided on this site is for informational purposes only and is not intended to replace the advice from your physician or other health care professional.
A poor diet can have an injurious impact on health, causing deficiency diseases such as scurvy, beriberi, and kwashiorkor; health-threatening conditions like obesity and metabolic syndrome, and such common chronic systemic diseases as cardiovascular disease, diabetes, and osteoporosis.

Contents

Animal nutrition

===Overview=== my mom sucks bslls
Nutritional science investigates the metabolic and physiological responses of the body to diet. With advances in the fields of molecular biology, biochemistry, and genetics, the study of nutrition is increasingly concerned with metabolism and metabolic pathways: the sequences of biochemical steps through which substances in living things change from one form to another.
A carnivore and herbivore diet is contrasting, with basic nitrogen and carbon proportions being at varying levels in particular foods. Carnivore nutrition has more nitrogen than carbon and herbivore nutrition contains less nitrogen than carbon, when an equal quantity is measured. Nitrogen is the predominant source of energy for organisms, through the nitrogen cycle, with various minerals and vitamins being equally vital. Nitrogen is also the primary energy for regular metabolic rates, this necessitates greater sums of plants for herbivore digestion, to absorb significant energy for sustenance and stamina.
The human body contains chemical compounds, such as water, carbohydrates (sugar, starch, and fiber), amino acids (in proteins), fatty acids (in lipids), and nucleic acids (DNA and RNA). These compounds in turn consist of elements such as carbon, hydrogen, oxygen, nitrogen, phosphorus, calcium, iron, zinc, magnesium, manganese, and so on. .All of these chemical compounds and elements occur in various forms and combinations (e.g.^ Despite wide variations in the nature of the external energy source utilized by various organisms, all organisms form from their external energy source an immediate source of energy, the chemical compound adenosine triphosphate (ATP).
  • nutrition -- Britannica Online Encyclopedia 8 January 2010 5:19 UTC www.britannica.com [Source type: Academic]

 ^ EHSs occur in practically all beach nourishment projects and some of these causes are related to the design and construction of the project.
  • Beach Nourishment - Coastal Geology 20 November 2009 10:16 UTC www.csc.noaa.gov [Source type: Academic]

 ^ And the all-important neurotransmitters are manufactured by the body from dietary precursors.  In order for this to occur, the B vitamins, magnesium, zinc, and Vitamin C must all be present in sufficient amounts.  These neurotransmitters are: .
  • Nutrition and ADD 8 January 2010 5:19 UTC borntoexplore.org [Source type: FILTERED WITH BAYES]

 hormones, vitamins, phospholipids, hydroxyapatite), both in the human body and in the plant and animal organisms that humans eat.
The human body consists of elements and compounds ingested, digested, absorbed, and circulated through the bloodstream to feed the cells of the body. Except in the unborn fetus, the digestive system is the first system involved. In a typical adult, about seven liters of digestive juices enter the lumen of the digestive tract.[citation needed] These break chemical bonds in ingested molecules, and modulate their conformations and energy states. Though some molecules are absorbed into the bloodstream unchanged, digestive processes release them from the matrix of foods. Unabsorbed matter, along with some waste products of metabolism, is eliminated from the body in the feces.
Studies of nutritional status must take into account the state of the body before and after experiments, as well as the chemical composition of the whole diet and of all material excreted and eliminated from the body (in urine and feces). Comparing the food to the waste can help determine the specific compounds and elements absorbed and metabolized in the body. The effects of nutrients may only be discernible over an extended period, during which all food and waste must be analyzed. The number of variables involved in such experiments is high, making nutritional studies time-consuming and expensive, which explains why the science of human nutrition is still slowly evolving.
In general, eating a wide variety of fresh, whole (unprocessed), foods has proven favorable compared to monotonous diets based on processed foods.[1] In particular, the consumption of whole-plant foods slows digestion and allows better absorption, and a more favorable balance of essential nutrients per Calorie, resulting in better management of cell growth, maintenance, and mitosis (cell division), as well as better regulation of appetite and blood sugar[citation needed]. Regularly scheduled meals (every few hours) have also proven more wholesome than infrequent or haphazard ones.[citation needed]

Nutrients

Main article: Nutrient
There are six major classes of nutrients: carbohydrates, fats, minerals, protein, vitamin, and water.
These nutrient classes can be categorized as either macronutrients (needed in relatively large amounts) or micronutrients (needed in smaller quantities). The macronutrients are carbohydrates, fats, fiber, proteins, and water. The micronutrients are minerals and vitamins.
The macronutrients (excluding fiber and water) provide structural material (amino acids from which proteins are built, and lipids from which cell membranes and some signaling molecules are built), energy. Some of the structural material can be used to generate energy internally, and in either case it is measured in Joules or kilocalories (often called "Calories" and written with a capital C to distinguish them from little 'c' calories). Carbohydrates and proteins provide 17 kJ approximately (4 kcal) of energy per gram, while fats provide 37 kJ (9 kcal) per gram.[2], though the net energy from either depends on such factors as absorption and digestive effort, which vary substantially from instance to instance. Vitamins, minerals, fiber, and water do not provide energy, but are required for other reasons. A third class dietary material, fiber (i.e., non-digestible material such as cellulose), seems also to be required, for both mechanical and biochemical reasons, though the exact reasons remain unclear.
Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. Carbohydrates range from simple monosaccharides (glucose, fructose, galactose) to complex polysaccharides (starch). Fats are triglycerides, made of assorted fatty acid monomers bound to glycerol backbone. Some fatty acids, but not all, are essential in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen. The fundamental components of protein are nitrogen-containing amino acids, some of which are essential in the sense that humans cannot make them internally. Some of the amino acids are convertible (with the expenditure of energy) to glucose and can be used for energy production just as ordinary glucose. By breaking down existing protein, some glucose can be produced internally; the remaining amino acids are discarded, primarily as urea in urine. This occurs normally only during prolonged starvation.
Other micronutrients include antioxidants and phytochemicals which are said to influence (or protect) some body systems. Their necessity is not as well established as in the case of, for instance, vitamins.
Most foods contain a mix of some or all of the nutrient classes, together with other substances such as toxins or various sorts. Some nutrients can be stored internally (e.g., the fat soluble vitamins), while others are required more or less continuously. Poor health can be caused by a lack of required nutrients or, in extreme cases, too much of a required nutrient. For example, both salt and water (both absolutely required) will cause illness or even death in too large amounts.

Carbohydrates

Main article: Carbohydrate
Toasted bread is a cheap, high calorie nutrient (usually unbalanced, i.e., deficient in essential minerals and vitamins, largely because of removal of both germ and bran during processing) food source.
Carbohydrates may be classified as monosaccharides, disaccharides, or polysaccharides depending on the number of monomer (sugar) units they contain. They constitute a large part of foods such as rice, noodles, bread, and other grain-based products. Monosaccharides contain one sugar unit, disaccharides two, and polysaccharides three or more. Polysaccharides are often referred to as complex carbohydrates because they are typically long multiple branched chains of sugar units. The difference is that complex carbohydrates take slightly longer to digest and absorb since their sugar units must be separated from the chain before absorption. The spike in blood glucose levels after ingestion of simple sugars is thought to be related to some of the heart and vascular diseases which have become more frequent in recent times. Simple sugars form a greater part of modern diets than formerly, perhaps leading to more cardiovascular disease. The degree of causation is still not clear, however.
Simple carbohydrates are absorbed quickly, and therefore raise blood-sugar levels more rapidly than other nutrients. However, the most important plant carbohydrate nutrient, starch, varies in its absorption. Gelatinized starch (starch heated for a few minutes in the presence of water) is far more digestible than plain starch. And starch which has been divided into fine particles is also more absorbable during digestion. The increased effort and decreased availability reduces the available energy from starchy foods substantially and can be seen experimentally in rats and anecdotally in humans. Additionally, up to a third of dietary starch may be unavailable due to mechanical or chemical difficulty.
Carbohydrates are not essential to the human diet, as they are relatively low in vitamins and minerals, and energy can be provided from excess fats and proteins in the diet.
Fiber
Main article: Dietary fiber
Dietary fiber is a carbohydrate (or a polysaccharide) that is incompletely absorbed in humans and in some animals. Like all carbohydrates, when it is metabolized it can produce four Calories (kilocalories) of energy per gram. But in most circumstances it accounts for less than that because of its limited absorption and digestibility. Dietary fiber consists mainly of cellulose, a large carbohydrate polymer that is indigestible because humans do not have the required enzymes to disassemble it. There are two subcategories: soluble and insoluble fiber. Whole grains, fruits (especially plums, prunes, and figs), and vegetables are good sources of dietary fiber. There are many health benefits of a high-fiber diet. Dietary fiber helps reduce the chance of gastrointestinal problems such as constipation and diarrhea by increasing the weight and size of stool and softening it. Insoluble fiber, found in whole-wheat flour, nuts and vegetables, especially stimulates peristalsis -- the rhythmic muscular contractions of the intestines which move digesta along the digestive tract. Soluble fiber, found in oats, peas, beans, and many fruits, helps dissolve water in the intestinal tract to produce a gel which slows the movement of food through the intestines. This may help lower blood glucose levels because it can slow the absorption of sugar. Additionally, fiber, perhaps especially that from whole grains,is thought to possibly help lessen insulin spikes, and therefore reduce the risk of type 2 diabetes. The link between increased fiber consumption and a decreased risk of colorectal cancer is still uncertain.[3]

Fat

Main article: Fat
A molecule of dietary fat typically consists of several fatty acids (containing long chains of carbon and hydrogen atoms), bonded to a glycerol. They are typically found as triglycerides (three fatty acids attached to one glycerol backbone). Fats may be classified as saturated or unsaturated depending on the detailed structure of the fatty acids involved. Saturated fats have all of the carbon atoms in their fatty acid chains bonded to hydrogen atoms, whereas unsaturated fats have some of these carbon atoms double-bonded, so their molecules have relatively fewer hydrogen atoms than a saturated fatty acid of the same length. Unsaturated fats may be further classified as monounsaturated (one double-bond) or polyunsaturated (many double-bonds). Furthermore, depending on the location of the double-bond in the fatty acid chain, unsaturated fatty acids are classified as omega-3 or omega-6 fatty acids. Trans fats are a type of unsaturated fat with trans-isomer bonds; these are rare in nature and in foods from natural sources; they are typically created in an industrial process called (partial) hydrogenation.
Saturated fats (typically from animal sources) are best in the human diet, as they have been a staple in many of the worlds cultures for many millennia. Unsaturated fats, (for example, vegetable oil) are next, while trans fats are to be avoided. Saturated and some trans fats are typically solid at room temperature (such as butter or lard), while unsaturated fats are typically liquids (such as olive oil or flaxseed oil). Trans fats are very rare in nature, but have properties useful in the food processing industry, such as rancidity resistance.[citation needed]
Essential fatty acids
Main article: Essential fatty acids
Most fatty acids are non-essential, meaning the body can produce them as needed, generally from other fatty acids and always by expending energy to do so. However, in humans at least two fatty acids are essential and must be included in the diet. An appropriate balance of essential fatty acids—omega-3 and omega-6 fatty acids—seems also important for health, though definitive experimental demonstration has been elusive. Both of these "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins, which have roles throughout the human body. They are hormones, in some respects. The omega-3 eicosapentaenoic acid (EPA), which can be made in the human body from the omega-3 essential fatty acid alpha-linolenic acid (LNA), or taken in through marine food sources, serves as a building block for series 3 prostaglandins (e.g. weakly inflammatory PGE3). The omega-6 dihomo-gamma-linolenic acid (DGLA) serves as a building block for series 1 prostaglandins (e.g. anti-inflammatory PGE1), whereas arachidonic acid (AA) serves as a building block for series 2 prostaglandins (e.g. pro-inflammatory PGE 2). Both DGLA and AA can be made from the omega-6 linoleic acid (LA) in the human body, or can be taken in directly through food. An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different prostaglandins: one reason a balance between omega-3 and omega-6 is believed important for cardiovascular health. In industrialized societies, people typically consume large amounts of processed vegetable oils, which have reduced amounts of the essential fatty acids along with too much of omega-6 fatty acids relative to omega-3 fatty acids.
The conversion rate of omega-6 DGLA to AA largely determines the production of the prostaglandins PGE1 and PGE2. Omega-3 EPA prevents AA from being released from membranes, thereby skewing prostaglandin balance away from pro-inflammatory PGE2 (made from AA) toward anti-inflammatory PGE1 (made from DGLA). Moreover, the conversion (desaturation) of DGLA to AA is controlled by the enzyme delta-5-desaturase, which in turn is controlled by hormones such as insulin (up-regulation) and glucagon (down-regulation). The amount and type of carbohydrates consumed, along with some types of amino acid, can influence processes involving insulin, glucagon, and other hormones; therefore the ratio of omega-3 versus omega-6 has wide effects on general health, and specific effects on immune function and inflammation, and mitosis (i.e. cell division).

Protein

Most meats such as chicken contain all the essential amino acids needed for humans
Main article: Protein in nutrition
Proteins are the basis of many animal body structures (e.g. muscles, skin, and hair). They also form the enzymes which control chemical reactions throughout the body. Each molecule is composed of amino acids which are characterized by inclusion of nitrogen and sometimes sulphur (these components are responsible for the distinctive smell of burning protein, such as the keratin in hair). The body requires amino acids to produce new proteins (protein retention) and to replace damaged proteins (maintenance). As there is no protein or amino acid storage provision, amino acids must be present in the diet. Excess amino acids are discarded, typically in the urine. For all animals, some amino acids are essential (an animal cannot produce them internally) and some are non-essential (the animal can produce them from other nitrogen-containing compounds). About twenty amino acids are found in the human body, and about ten of these are essential, and therefore must be included in the diet. A diet that contains adequate amounts of amino acids (especially those that are essential) is particularly important in some situations: during early development and maturation, pregnancy, lactation, or injury (a burn, for instance). A complete protein source contains all the essential amino acids; an incomplete protein source lacks one or more of the essential amino acids.
It is possible to combine two incomplete protein sources (e.g. rice and beans) to make a complete protein source, and characteristic combinations are the basis of distinct cultural cooking traditions. Sources of dietary protein include meats, tofu and other soy-products, eggs, legumes, and dairy products such as milk and cheese. Excess amino acids from protein can be converted into glucose and used for fuel through a process called gluconeogenesis. The amino acids remaining after such conversion are discarded.

Minerals

Main article: Dietary mineral
Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen that are present in nearly all organic molecules. The term "mineral" is archaic, since the intent is to describe simply the less common elements in the diet. Some are heavier than the four just mentioned—including several metals, which often occur as ions in the body. Some dietitians recommend that these be supplied from foods in which they occur naturally, or at least as complex compounds, or sometimes even from natural inorganic sources (such as calcium carbonate from ground oyster shells). Some are absorbed much more readily in the ionic forms found in such sources. On the other hand, minerals are often artificially added to the diet as supplements; the most famous is likely iodine in iodized salt which prevents goiter.
Macrominerals
Many elements are essential in relative quantity; they are usually called "bulk minerals". Some are structural, but many play a role as electrolytes.[4] Elements with recommended dietary allowance (RDA) greater than 200 mg/day are, in alphabetical order (with informal or folk-medicine perspectives in parentheses):
  • Calcium, a common electrolyte, but also needed structurally (for muscle and digestive system health, bones, some forms neutralizes acidity, may help clear toxins, and provide signaling ions for nerve and membrane functions)
  • Chlorine as chloride ions; very common electrolyte; see sodium, below
  • Magnesium, required for processing ATP and related reactions (builds bone, causes strong peristalsis, increases flexibility, increases alkalinity)
  • Phosphorus, required component of bones; essential for energy processing[5]
  • Potassium, a very common electrolyte (heart and nerve health)
  • Sodium, a very common electrolyte; not generally found in dietary supplements, despite being needed in large quantities, because the ion is very common in food: typically as sodium chloride, or common salt. Excessive sodium consumption can deplete calcium and magnesium, leading to high blood pressure and osteoporosis.
  • Sulfur for three essential amino acids and therefore many proteins (skin, hair, nails, liver, and pancreas)
Trace minerals
Many elements are required in trace amounts, usually because they play a catalytic role in enzymes.[6] Some trace mineral elements (RDA < 200 mg/day) are, in alphabetical order:

Vitamins

Main article: Vitamin
As with the minerals discussed above, some vitamins are recognized as essential nutrients, necessary in the diet for good health. (Vitamin D is the exception: it can alternatively be synthesized in the skin, in the presence of UVB radiation.) Certain vitamin-like compounds that are recommended in the diet, such as carnitine, are thought useful for survival and health, but these are not "essential" dietary nutrients because the human body has some capacity to produce them from other compounds. Moreover, thousands of different phytochemicals have recently been discovered in food (particularly in fresh vegetables), which may have desirable properties including antioxidant activity (see below); experimental demonstration has been suggestive but inconclusive. Other essential nutrients not classed as vitamins include essential amino acids (see above), choline, essential fatty acids (see above), and the minerals discussed in the preceding section.
Vitamin deficiencies may result in disease conditions: goitre, scurvy, osteoporosis, impaired immune system, disorders of cell metabolism, certain forms of cancer, symptoms of premature aging, and poor psychological health (including eating disorders), among many others.[7] Excess of some vitamins is also dangerous to health (notably vitamin A), and for at least one vitamin, B6, toxicity begins at levels not far above the required amount. Deficiency or excess of minerals can also have serious health consequences.

Water

Main article: Drinking water
A manual water pump in China
It is not fully clear how much water intake is needed by healthy people, although some assert that 6–8 glasses of water daily is the minimum to maintain proper hydration.[8] The notion that a person should consume eight glasses of water per day cannot be traced to a credible scientific source.[9] The effect of, greater or lesser, water intake on weight loss and on constipation is also still unclear.[10] The original water intake recommendation in 1945 by the Food and Nutrition Board of the National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods."[11] The latest dietary reference intake report by the United States National Research Council recommended, generally, (including food sources): 2.7 liters of water total for women and 3.7 liters for men.[12] Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. According to the Institute of Medicine—who recommend that, on average, women consume 2.2 litres and men 3.0 litres—this is recommended to be 2.4 litres (approx. 9 cups) for pregnant women and 3 litres (approx. 12.5 cups) for breastfeeding women since an especially large amount of fluid is lost during nursing.[13]
For those who have healthy kidneys, it is somewhat difficult to drink too much water,[citation needed] but (especially in warm humid weather and while exercising) it is dangerous to drink too little. People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which can be fatal. In particular large amounts of de-ionized water are dangerous.
Normally, about 20 percent of water intake comes in food, while the rest comes from drinking water and assorted beverages (caffeinated included). Water is excreted from the body in multiple forms; including urine and feces, sweating, and by water vapor in the exhaled breath.

Other nutrients

Other micronutrients include antioxidants and phytochemicals. These substances are generally more recent discoveries which have not yet been recognized as vitamins or as required. Phytochemicals may act as antioxidants, but not all phytochemicals are antioxidants.[citation needed]
Antioxidants
Main article: Antioxidant
.As cellular metabolism/energy production requires oxygen, potentially damaging (e.g.^ However, the human body is not as efficient as a calorimeter, and some potential energy is lost during digestion and metabolism.
  • human nutrition -- Britannica Online Encyclopedia 8 January 2010 5:19 UTC www.britannica.com [Source type: FILTERED WITH BAYES]

 ^ Usage Magnesium is essential for the production of ATP, the body's primary energy producing molecule, as well as for the manufacture of protein by cellular ribosomes.
  • Nutrition - Find great deals, lowest prices, and buy Nutrition at Shopping.com 8 January 2010 5:19 UTC www.shopping.com [Source type: General]

 mutation causing) compounds known as free radicals can form. Most of these are oxidizers (i.e. acceptors of electrons) and some react very strongly. For normal cellular maintenance, growth, and division, these free radicals must be sufficiently neutralized by antioxidant compounds. Recently, some researchers suggested an interesting theory of evolution of dietary antioxidants. Some are produced by the human body with adequate precursors (glutathione, Vitamin C) and those the body cannot produce may only be obtained in the diet via direct sources (Vitamin C in humans, Vitamin A, Vitamin K) or produced by the body from other compounds (Beta-carotene converted to Vitamin A by the body, Vitamin D synthesized from cholesterol by sunlight). Phytochemicals (Section Below) and their subgroup polyphenols are the majority of antioxidants; about 4,000 are known. Different antioxidants are now known to function in a cooperative network, e.g. vitamin C can reactivate free radical-containing glutathione or vitamin E by accepting the free radical itself, and so on. .Some antioxidants are more effective than others at neutralizing different free radicals.^ Specifically, antioxidants work to slow down the rate of oxidative damage by gathering up free radicals that form when body cells use oxygen.
  • BarleyFoods | Health & Nutrition 8 January 2010 5:19 UTC www.barleyfoods.org [Source type: Academic]

 ^ Almost 65 000 consumers took advantage of the free checks during the four-day campaign and the website received more than 150 000 hits.
  • Nutrition | Unilever Global 8 January 2010 5:19 UTC www.unilever.com [Source type: FILTERED WITH BAYES]

 ^ Deduction limited to $200 for each child under age 2 and not more than $175 for each other dependent.
  • 2008 Farm Bill Side-by-Side: Title IV: Nutrition 8 January 2010 5:19 UTC www.ers.usda.gov [Source type: FILTERED WITH BAYES]

 Some cannot neutralize certain free radicals. Some cannot be present in certain areas of free radical development (Vitamin A is fat-soluble and protects fat areas, Vitamin C is water soluble and protects those areas). .When interacting with a free radical, some antioxidants produce a different free radical compound that is less dangerous or more dangerous than the previous compound.^ Specifically, antioxidants work to slow down the rate of oxidative damage by gathering up free radicals that form when body cells use oxygen.
  • BarleyFoods | Health & Nutrition 8 January 2010 5:19 UTC www.barleyfoods.org [Source type: Academic]

 ^ Almost 65 000 consumers took advantage of the free checks during the four-day campaign and the website received more than 150 000 hits.
  • Nutrition | Unilever Global 8 January 2010 5:19 UTC www.unilever.com [Source type: FILTERED WITH BAYES]

 ^ Nutrition And Beauty: Fats Create Skin Radiance You deprive yourself of more than fats when you go for the fat-free or low-fat salad dressing.
  • Nutrition Facts - Nutrition Information Articles 8 January 2010 5:19 UTC www.buzzle.com [Source type: General]

 Having a variety of antioxidants allows any byproducts to be safely dealt with by more efficient antioxidants in neutralizing a free radical's butterfly effect.
Although initial studies suggested that antioxidant supplements might promote health, later large clinical trials did not detect any benefit and suggested instead that excess supplementation may be harmful.[14]
Phytochemicals
Blackberries are a source of polyphenol antioxidants
Main article: Phytochemical
A growing area of interest is the effect upon human health of trace chemicals, collectively called phytochemicals. These nutrients are typically found in edible plants, especially colorful fruits and vegetables, but also other organisms including seafood, algae, and fungi. The effects of phytochemicals increasingly survive rigorous testing by prominent health organizations. One of the principal classes of phytochemicals are polyphenol antioxidants, chemicals which are known to provide certain health benefits to the cardiovascular system and immune system. These chemicals are known to down-regulate the formation of reactive oxygen species, key chemicals in cardiovascular disease.
Perhaps the most rigorously tested phytochemical is zeaxanthin, a yellow-pigmented carotenoid present in many yellow and orange fruits and vegetables. Repeated studies have shown a strong correlation between ingestion of zeaxanthin and the prevention and treatment of age-related macular degeneration (AMD).[15] Less rigorous studies have proposed a correlation between zeaxanthin intake and cataracts.[16] .A second carotenoid, lutein, has also been shown to lower the risk of contracting AMD. Both compounds have been observed to collect in the retina when ingested orally, and they serve to protect the rods and cones against the destructive effects of light.^ Diet and cancer studies have shown that, in general, vegetables and fruits, dietary fiber, and certain nutrients seem to be protective against cancer, whereas fat, excessive calories, and alcohol are linked to increased risk.
  • Bladder Cancer WebCaf� - Nutrition 8 January 2010 5:19 UTC blcwebcafe.org [Source type: Academic]

 ^ The cancer incidence was then compared with dietary intake of any of 46 fruits, vegetables, and related products to see if any of these foods had a protective effect against prostate cancer.
  • Bladder Cancer WebCaf� - Nutrition 8 January 2010 5:19 UTC blcwebcafe.org [Source type: Academic]

 ^ Higher plants, for example, are photolithotrophic; i.e., they utilize light energy, with the inorganic compound water serving as the ultimate electron donor .
  • nutrition -- Britannica Online Encyclopedia 8 January 2010 5:19 UTC www.britannica.com [Source type: Academic]
Another carotenoid, beta-cryptoxanthin, appears to protect against chronic joint inflammatory diseases, such as arthritis. .While the association between serum blood levels of beta-cryptoxanthin and substantially decreased joint disease has been established, neither a convincing mechanism for such protection nor a cause-and-effect have been rigorously studied.^ The insulin causes a sharp drop in blood sugar level in about 30 minutes.
  • Nutrition for the Athlete 8 January 2010 5:19 UTC www.ext.colostate.edu [Source type: FILTERED WITH BAYES]

 ^ Few studies have found significant effects on HIV transmission, disease progression or death rates.
  • HIV and nutrition 8 January 2010 5:19 UTC www.avert.org [Source type: Academic]

 ^ One study found a daily consumption of 40 milligrams (mgs) did boost blood levels of carotenoids.

 [17] Similarly, a red phytochemical, lycopene, has substantial credible evidence of negative association with development of prostate cancer.
The correlations between the ingestion of some phytochemicals and the prevention of disease are, in some cases, enormous in magnitude.
Even when the evidence is obtained, translating it to practical dietary advice can be difficult and counter-intuitive. .Lutein, for example, occurs in many yellow and orange fruits and vegetables and protects the eyes against various diseases.^ The lycopene in these foods is one of five groups of carotenoids: No measurable protective effect against prostate cancer was noted among the four other primary carotenoids: alpha carotene (found in carrots), beta carotene (in yams, sweet potatoes, yellow squash), lutein (found in dark green, leafy vegetables), and beta-cryptoxanthin (in oranges).
  • Bladder Cancer WebCaf� - Nutrition 8 January 2010 5:19 UTC blcwebcafe.org [Source type: Academic]

 ^ Although dark green and yellow-orange vegetables are usually recommended for their abundance of carotenoids, one recent study has found that the carotenoid lycopene, a pigment that is responsible for the color of tomatoes and other red fruits and vegetables, is a very potent antioxidant and may protect against colon and bladder cancer.
  • Bladder Cancer WebCaf� - Nutrition 8 January 2010 5:19 UTC blcwebcafe.org [Source type: Academic]

 ^ Falcarinol protects carrots and other vegetables in the same family from fungal diseases.
  • Bladder Cancer WebCaf� - Nutrition 8 January 2010 5:19 UTC blcwebcafe.org [Source type: Academic]

 However, it does not protect the eye nearly as well as zeaxanthin, and the presence of lutein in the retina will prevent zeaxanthin uptake. .Additionally, evidence has shown that the lutein present in egg yolk is more readily absorbed than the lutein from vegetable sources, possibly because of fat solubility.^ Nutrition And Beauty: Fats Create Skin Radiance You deprive yourself of more than fats when you go for the fat-free or low-fat salad dressing.
  • Nutrition Facts - Nutrition Information Articles 8 January 2010 5:19 UTC www.buzzle.com [Source type: General]

 ^ In fact, it contains more monounsaturated fats (13mg per ounce) than saturated fats (11g per ounce).
  • The Nutrition Data Blog by Monica Reinagel 8 January 2010 5:19 UTC blog.nutritiondata.com [Source type: General]

 ^ There is no evidence that taking more vitamins than is obtained by eating a variety of foods will improve performance.
  • Nutrition for the Athlete 8 January 2010 5:19 UTC www.ext.colostate.edu [Source type: FILTERED WITH BAYES]

 [18] .At the most basic level, the question "should you eat eggs?"^ Here we discuss what you should and should not be eating to minimize your risk of heart disease, and examine the role of a heart health supplement.
  • Nutrition Facts - Nutrition Information Articles 8 January 2010 5:19 UTC www.buzzle.com [Source type: General]

 ^ Now take a look below to find out what foods you should eat to get those calories.
  • Nutrition 8 January 2010 5:19 UTC wrestlegirl.com [Source type: FILTERED WITH BAYES]

 ^ The times when you are weak and do not feel like eating are the times when you need the energy, protein and protective factors from foods most.

 is complex to the point of dismay, including misperceptions about the health effects of cholesterol in egg yolk, and its saturated fat content.
As another example, lycopene is prevalent in tomatoes (and actually is the chemical that gives tomatoes their red color). It is more highly concentrated, however, in processed tomato products such as commercial pasta sauce, or tomato soup, than in fresh "healthy" tomatoes. Yet, such sauces tend to have high amounts of salt, sugar, other substances a person may wish or even need to avoid.
The following table presents phytochemical groups and common sources, arranged by family:
Family Sources Possible Benefits
flavonoids berries, herbs, vegetables, wine, grapes, tea general antioxidant, oxidation of LDLs, prevention of arteriosclerosis and heart disease
isoflavones (phytoestrogens) soy, red clover, kudzu root general antioxidant, prevention of arteriosclerosis and heart disease, easing symptoms of menopause, cancer prevention[19]
isothiocyanates cruciferous vegetables cancer prevention
monoterpenes citrus peels, essential oils, herbs, spices, green plants, atmosphere[20] cancer prevention, treating gallstones
organosulfur compounds chives, garlic, onions cancer prevention, lowered LDLs, assistance to the immune system
saponins beans, cereals, herbs Hypercholesterolemia, Hyperglycemia, Antioxidant, cancer prevention,
capsaicinoids all capiscum (chile) peppers topical pain relief, cancer prevention, cancer cell apoptosis

Intestinal bacterial flora

Main article: Gut flora
It is now also known that animal intestines contain a large population of gut flora. In humans, these include species such as Bacteroides, L. acidophilus and E. coli, among many others. They are essential to digestion, and are also affected by the food we eat. Bacteria in the gut perform many important functions for humans, including breaking down and aiding in the absorption of otherwise indigestible food; stimulating cell growth; repressing the growth of harmful bacteria, training the immune system to respond only to pathogens; producing vitamin B12, and defending against some infectious diseases.

Advice and guidance

Governmental policies

The updated USDA food pyramid, published in 2005, is a general nutrition guide for recommended food consumption for humans.
In the US, dietitians are registered (RD) or licensed (LD) with the Commission for Dietetic Registration and the American Dietetic Association, and are only able to use the title "dietitian," as described by the business and professions codes of each respective state, when they have met specific educational and experiential prerequisites and passed a national registration or licensure examination, respectively. In California, registered dietitians must abide by the "Business and Professions Code of Section 2585-2586.8". http://www.leginfo.ca.gov/cgi-bin/displaycode?section=bpc&group=02001-03000&file=2585-2586.8. Anyone may call themselves a nutritionist, including unqualified dietitians, as this term is unregulated. Some states, such as the State of Florida, have begun to include the title "nutritionist" in state licensure requirements. Most governments provide guidance on nutrition, and some also impose mandatory disclosure/labeling requirements for processed food manufacturers and restaurants to assist consumers in complying with such guidance.
In the US, nutritional standards and recommendations are established jointly by the US Department of Agriculture and US Department of Health and Human Services. Dietary and physical activity guidelines from the USDA are presented in the concept of a food pyramid, which superseded the Four Food Groups. The Senate committee currently responsible for oversight of the USDA is the Agriculture, Nutrition and Forestry Committee. Committee hearings are often televised on C-SPAN as seen here.
The U.S. Department of Health and Human Services provides a sample week-long menu which fulfills the nutritional recommendations of the government.[21] Canada's Food Guide is another governmental recommendation.

Teaching

Nutrition is taught in schools in many countries. In England and Wales the Personal and Social Education and Food Technology curricula include nutrition, stressing the importance of a balanced diet and teaching how to read nutrition labels on packaging. In many schools a Nutrition class will fall within the Family and Consumer Science or Health departments. In some American schools, students are required to take a certain number of FCS or Health related classes. Nutrition is offered at many schools, and if it is not a class of its own, nutrition is included in other FCS or Health classes such as: Life Skills, Independent Living, Single Survival, Freshmen Connection, Health etc. In many Nutrition classes, students learn about the food groups, the food pyramid, Daily Recommended Allowances, calories, vitamins, minerals, malnutrition, physical activity, healthy food choices and how to live a healthy life.
A 1985 US National Research Council report entitled Nutrition Education in US Medical Schools concluded that nutrition education in medical schools was inadequate.[22] Only 20% of the schools surveyed taught nutrition as a separate, required course. A 2006 survey found that this number had risen to 30%.[23]

Healthy diets

Main article: Healthy diet

Whole plant food diet

.Heart disease, cancer, obesity, and diabetes are commonly called "Western" diseases because these maladies were once rarely seen in developing countries.^ Offers advice that will help to promote health and reduce risk for chronic diseases such as heart disease, certain cancers, diabetes, stroke, and osteoporosis.
  • U.S. Government Bookstore: Browse by Subject: Nutrition 8 January 2010 5:19 UTC bookstore.gpo.gov [Source type: Academic]

 ^ Metformin, commonly used to treat non-insulin-dependent (type II) diabetes, can improve insulin function and reduce risk factors for heart disease.
  • HRSACareAction - Providing HIV/AIDS Care in a Changing Environment - August 2004 8 January 2010 5:19 UTC hab.hrsa.gov [Source type: Academic]

 ^ Did you know that you can drastically decrease your chance of heart disease and cancer by eating a healthy diet and following the recommended nutrition guidelines?
  • Nutrition Facts - Nutrition Information Articles 8 January 2010 5:19 UTC www.buzzle.com [Source type: General]

 One study in China found some regions had essentially no cancer or heart disease, while in other areas they reflected "up to a 100-fold increase" coincident with diets that were found to be entirely plant-based to heavily animal-based, respectively.[24] .In contrast, diseases of affluence like cancer and heart disease are common throughout the United States.^ Offers advice that will help to promote health and reduce risk for chronic diseases such as heart disease, certain cancers, diabetes, stroke, and osteoporosis.
  • U.S. Government Bookstore: Browse by Subject: Nutrition 8 January 2010 5:19 UTC bookstore.gpo.gov [Source type: Academic]

 ^ Did you know that you can drastically decrease your chance of heart disease and cancer by eating a healthy diet and following the recommended nutrition guidelines?
  • Nutrition Facts - Nutrition Information Articles 8 January 2010 5:19 UTC www.buzzle.com [Source type: General]

 ^ Much is made of the fact that vegetarians have lower rates of heart disease and cancer.
  • The Nutrition Data Blog by Monica Reinagel 8 January 2010 5:19 UTC blog.nutritiondata.com [Source type: General]

 Adjusted for age and exercise, large regional clusters of people in China rarely suffered from these "Western" diseases possibly because their diets are rich in vegetables, fruits and whole grains.[24]
.The United Healthcare/Pacificare nutrition guideline recommends a whole plant food diet, and recommends using protein only as a condiment with meals.^ Foods - Nutrition recommendations .
  • human nutrition -- Britannica Online Encyclopedia 8 January 2010 5:19 UTC www.britannica.com [Source type: FILTERED WITH BAYES]

 ^ Poor diet: poor food choices, bingeing, skipping meals, high sugar intake, high alcohol consumption, high intake of refined foods, low fruit and vegetable intake, insufficient protein, insufficient calcium, food allergies or intolerances limiting intake .
  • Nutrition 8 January 2010 5:19 UTC aidsetc.org [Source type: Academic]

 ^ Lentils Nutritional Value Lentils nutritional value can be inferred from the fact that these pulses have the third highest level of protein, by weight, of any plant-based food.
  • Nutrition Facts - Nutrition Information Articles 8 January 2010 5:19 UTC www.buzzle.com [Source type: General]

 A National Geographic cover article from November, 2005, entitled The Secrets of Living Longer, also recommends a whole plant food diet. The article is a lifestyle survey of three populations, Sardinians, Okinawans, and Adventists, who generally display longevity and "suffer a fraction of the diseases that commonly kill people in other parts of the developed world, and enjoy more healthy years of life." In sum, they offer three sets of 'best practices' to emulate. The rest is up to you. .In common with all three groups is to "Eat fruits, vegetables, and whole grains."^ Eat a variety of nutrients from the four food groups.* A. Consume four or more servings a day from the Beans, grains, & Nuts, and the Fruit & Vegetable groups.

 ^ We’re used to eating some type of vegetable with every meal and fruit every day,” Ms. Leonard said.

 ^ We need fats to absorb all the beneficial elements of salads and other fruits and vegetables.
  • Nutrition Facts - Nutrition Information Articles 8 January 2010 5:19 UTC www.buzzle.com [Source type: General]
The National Geographic article noted that an NIH funded study of 34,000 Seventh-day Adventists between 1976 and 1988 "...found that the Adventists' habit of consuming beans, soy milk, tomatoes, and other fruits lowered their risk of developing certain cancers. .It also suggested that eating whole grain bread, drinking five glasses of water a day, and, most surprisingly, consuming four servings of nuts a week reduced their risk of heart disease.^ Eat a variety of nutrients from the four food groups.* A. Consume four or more servings a day from the Beans, grains, & Nuts, and the Fruit & Vegetable groups.

 ^ Hispanic woman drinking glass of water .
  • Nourishment Images and Stock Photos. 25440 Nourishment photography and royalty free pictures available to download from over 100 stock photo companies. 20 November 2009 10:16 UTC www.fotosearch.com [Source type: General]

 ^ Tuna salad on whole grain bread .
  • Nourishment Images and Stock Photos. 25440 Nourishment photography and royalty free pictures available to download from over 100 stock photo companies. 20 November 2009 10:16 UTC www.fotosearch.com [Source type: General]

 "

The French "paradox"

Main article: French paradox
The French paradox is the observation that the French suffer a relatively low incidence of coronary heart disease, despite having a diet relatively rich in saturated fats. A number of explanations have been suggested:
  • Reduced consumption of processed carbohydrate and other junk foods.
  • Regular consumption of red wine.
  • More active lifestyles involving plenty of daily exercise, especially walking; the French are much less dependent on cars than Americans are.
  • Higher consumption of artificially produced trans-fats by Americans, which has been shown to have greater lipoprotein effects per gram than saturated fat.[25]
However, statistics collected by the World Health Organization from 1990-2000 show that the incidence of heart disease in France may have been underestimated and in fact be similar to that of neighboring countries.[26]

Sports nutrition

Main article: Sports nutrition

Protein

Protein milkshakes, made from protein powder (center) and milk (left), are a common bodybuilding supplement.
Protein is an important component of every cell in the body. Hair and nails are mostly made of protein. The body uses protein to build and repair tissues. Also protein is used to make enzymes, hormones, and other body chemicals. Protein is an important building block of bones, muscles, cartilage, skin, and blood.
The protein requirement for each individual differs, as do opinions about whether and to what extent physically active people require more protein. The 2005 Recommended Dietary Allowances (RDA), aimed at the general healthy adult population, provide for an intake of 0.8 - 1 grams of protein per kilogram of body weight (according to the BMI formula), with the review panel stating that "no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise".[27] Conversely, Di Pasquale (2008), citing recent studies, recommends a minimum protein intake of 2.2 g/kg "for anyone involved in competitive or intense recreational sports who wants to maximize lean body mass but does not wish to gain weight".[28]

Water and salts

Water is one of the most important nutrients in the sports diet. It helps eliminate food waste products in the body, regulates body temperature during activity and helps with digestion. Maintaining hydration during periods of physical exertion is key to peak performance. While drinking too much water during activities can lead to physical discomfort, dehydration in excess of 2% of body mass (by weight) markedly hinders athletic performance[29]. Additional carbohydrates and protein before, during, and after exercise increase time to exhaustion as well as speed recovery. Dosage is based on work performed, lean body mass, and environmental factors, especially ambient temperature and humidity. Maintaining the right amount is key.

Carbohydrates

The main fuel used by the body during exercise is carbohydrates, which is stored in muscle as glycogen—a form of sugar. During exercise, muscle glycogen reserves can be used up, especially when activities last longer than 90 min.[citation needed] .Because the amount of glycogen stored in the body is limited, it is important for athletes to replace glycogen by consuming a diet high in carbohydrates.^ Fad Diets Analyzed In this article, we will examine the scientific pros and cons regarding low carbohydrate, high protein diets such as the Atkins and South Beach diets in managing our weight and achieving optimal body composition.
  • Nutrition Section @ Chiro.Org 8 January 2010 5:19 UTC www.chiro.org [Source type: Academic]

 ^ I found it to be interesting because it says that it doesn't matter what kind of diet change one under goes, low carb, high carb, high protein, hig...
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 ^ Several studies, that compared high fat or low carbohydrate diets to mixed or high carbohydrate diets, demonstrated a significant performance advantage to the high carbohydrate groups (Keith, 1989).

 .Meeting energy needs can help improve performance during the sport, as well as improve overall strength and endurance.^ Your doctor can help you assess your nutritional needs and make suggestions for meeting them.
  • Nutrition for Seniors: Healthy Eating Tips for Older Adults 8 January 2010 5:19 UTC www.helpguide.org [Source type: General]

 ^ Whether your playing sports or just playing with the kids next door, eating healthy will improve your overall ability.
There are different kinds of carbohydrates—simple or refined, and unrefined. A typical American consumes about 50% of their carbohydrates as simple sugars, which are added to foods as opposed to sugars that come naturally in fruits and vegetables. These simple sugars come in large amounts in sodas and fast food. Over the course of a year, the average American consumes 54 gallons of soft drinks, which contain the highest amount of added sugars.[30] Even though carbohydrates are necessary for humans to function, they are not all equally healthful. When machinery has been used to remove bits of high fiber, the carbohydrates are refined. These are the carbohydrates found in white bread and fast food.[31]

Malnutrition

Main article: Malnutrition
Malnutrition refers to insufficient, excessive, or imbalanced consumption of nutrients. In developed countries, the diseases of malnutrition are most often associated with nutritional imbalances or excessive consumption. Although there are more people in the world who are malnourished due to excessive consumption, according to the United Nations World Health Organization, the real challenge in developing nations today, more than starvation, is combating insufficient nutrition — the lack of nutrients necessary for the growth and maintenance of vital functions.

Illnesses caused by improper nutrient consumption

Nutrients Deficiency Excess
Macronutrients
Calories Starvation, Marasmus Obesity, diabetes mellitus, Cardiovascular disease
Simple carbohydrates none diabetes mellitus, Obesity
Complex carbohydrates micronutrient deficiency Obesity
Protein kwashiorkor Rabbit starvation, Ketoacidosis, kidney disease
Saturated fat none Obesity, Cardiovascular Disease
Trans fat none Obesity, Cardiovascular Disease
Unsaturated fat fat-soluble vitamin deficiency Obesity, Cardiovascular disease
Micronutrients
Vitamin A Xerophthalmia and Night Blindness Hypervitaminosis A (cirrhosis, hair loss)
Vitamin B1 Beri-Beri
Vitamin B2 Cracking of skin and Corneal Unclearation
Niacin Pellagra dyspepsia, cardiac arrhythmias, birth defects
Vitamin B12 Pernicious Anemia
Vitamin C Scurvy diarrhea causing dehydration
Vitamin D Rickets Hypervitaminosis D (dehydration, vomiting, constipation)
Vitamin E neurological disease Hypervitaminosis E (anticoagulant: excessive bleeding)
Vitamin K Hemorrhage
Omega 3 Fats Cardiovascular Disease Bleeding, Hemorrhages, Hemorrhagic stroke, reduced glycemic control among diabetics
Omega 6 Fats none Cardiovascular Disease, Cancer
Cholesterol none Cardiovascular Disease
Macrominerals
Calcium Osteoporosis, tetany, carpopedal spasm, laryngospasm, cardiac arrhythmias Fatigue, depression, confusion, nausea, vomiting, constipation, pancreatitis, increased urination, kidney stones
Magnesium Hypertension Weakness, nausea, vomiting, impaired breathing, and hypotension
Potassium Hypokalemia, cardiac arrhythmias Hyperkalemia, palpitations
Sodium hyponatremia Hypernatremia, hypertension
Trace minerals
Iron Anemia Cirrhosis, Hepatitis C, heart disease
Iodine Goiter, hypothyroidism Iodine Toxicity (goiter, hypothyroidism)

Mental agility

Main article: Nootropic
Research indicates that improving the awareness of nutritious meal choices and establishing long-term habits of healthy eating has a positive effect on a cognitive and spatial memory capacity, potentially increasing a student's potential to process and retain academic information.
Some organizations have begun working with teachers, policymakers, and managed foodservice contractors to mandate improved nutritional content and increased nutritional resources in school cafeterias from primary to university level institutions. Health and nutrition have been proven to have close links with overall educational success.[32] Currently less than 10% of American college students report that they eat the recommended five servings of fruit and vegetables daily.[33] Better nutrition has been shown to have an impact on both cognitive and spatial memory performance; a study showed those with higher blood sugar levels performed better on certain memory tests.[34] In another study, those who consumed yogurt performed better on thinking tasks when compared to those who consumed caffeine free diet soda or confections.[35] Nutritional deficiencies have been shown to have a negative effect on learning behavior in mice as far back as 1951.[36]
"Better learning performance is associated with diet induced effects on learning and memory ability".[37]
The "nutrition-learning nexus" demonstrates the correlation between diet and learning and has application in a higher education setting.
"We find that better nourished children perform significantly better in school, partly because they enter school earlier and thus have more time to learn but mostly because of greater learning productivity per year of schooling."[38]
91% of college students feel that they are in good health while only 7% eat their recommended daily allowance of fruits and vegetables.[33]
Nutritional education is an effective and workable model in a higher education setting.[39][40]
More "engaged" learning models that encompass nutrition is an idea that is picking up steam at all levels of the learning cycle.[41]
There is limited research available that directly links a student's Grade Point Average (G.P.A.) to their overall nutritional health. Additional substantive data is needed to prove that overall intellectual health is closely linked to a person's diet, rather than just another correlation fallacy.

Mental disorders

Nutritional supplement treatment may be appropriate for major depression, bipolar disorder, schizophrenia, and obsessive compulsive disorder, the four most common mental disorders in developed countries.[42] Supplements that have been studied most for mood elevation and stabilization include eicosapentaenoic acid and docosahexaenoic acid (each of which are an omega-3 fatty acid contained in fish oil, but not in flaxseed oil), vitamin B12, folic acid, and inositol.

Cancer

Cancer is now common in developing countries. According to a study by the International Agency for Research on Cancer, "In the developing world, cancers of the liver, stomach and esophagus were more common, often linked to consumption of carcinogenic preserved foods, such as smoked or salted food, and parasitic infections that attack organs." Lung cancer rates are rising rapidly in poorer nations because of increased use of tobacco. Developed countries "tended to have cancers linked to affluence or a 'Western lifestyle' — cancers of the colon, rectum, breast and prostate — that can be caused by obesity, lack of exercise, diet and age."[43]

Metabolic syndrome

Several lines of evidence indicate lifestyle-induced hyperinsulinemia and reduced insulin function (i.e. insulin resistance) as a decisive factor in many disease states. For example, hyperinsulinemia and insulin resistance are strongly linked to chronic inflammation, which in turn is strongly linked to a variety of adverse developments such as arterial microinjuries and clot formation (i.e. heart disease) and exaggerated cell division (i.e. cancer). Hyperinsulinemia and insulin resistance (the so-called metabolic syndrome) are characterized by a combination of abdominal obesity, elevated blood sugar, elevated blood pressure, elevated blood triglycerides, and reduced HDL cholesterol. The negative impact of hyperinsulinemia on prostaglandin PGE1/PGE2 balance may be significant.
The state of obesity clearly contributes to insulin resistance, which in turn can cause type 2 diabetes. .Virtually all obese and most type 2 diabetic individuals have marked insulin resistance.^ Metformin, commonly used to treat non-insulin-dependent (type II) diabetes, can improve insulin function and reduce risk factors for heart disease.
  • HRSACareAction - Providing HIV/AIDS Care in a Changing Environment - August 2004 8 January 2010 5:19 UTC hab.hrsa.gov [Source type: Academic]

 ^ Other side effects of antiretroviral treatment include insulin resistance, which can occasionally lead to diabetes.
  • HIV and nutrition 8 January 2010 5:19 UTC www.avert.org [Source type: Academic]

 ^ Soluble fiber may also help reduce the risk of developing type 2 or non-insulin-dependent diabetes.
  • BarleyFoods | Health & Nutrition 8 January 2010 5:19 UTC www.barleyfoods.org [Source type: Academic]

 Although the association between overweight and insulin resistance is clear, the exact (likely multifarious) causes of insulin resistance remain less clear. Importantly, it has been demonstrated that appropriate exercise, more regular food intake and reducing glycemic load (see below) all can reverse insulin resistance in overweight individuals (and thereby lower blood sugar levels in those who have type 2 diabetes).
.Obesity can unfavourably alter hormonal and metabolic status via resistance to the hormone leptin, and a vicious cycle may occur in which insulin/leptin resistance and obesity aggravate one another.^ An early first menstrual period, before the age of 12, is a risk factor for breast cancer, teenage depression, obesity and insulin resistance.

 ^ After exercising in hot and humid environments for one hour a water loss of up to .5 lbs per mile may occur.

 ^ Metabolic abnormalities alter the way the body uses, stores, and excretes nutrients and may result in an increased need for calories and protein.
  • HRSACareAction - Providing HIV/AIDS Care in a Changing Environment - August 2004 8 January 2010 5:19 UTC hab.hrsa.gov [Source type: Academic]

 .The vicious cycle is putatively fuelled by continuously high insulin/leptin stimulation and fat storage, as a result of high intake of strongly insulin/leptin stimulating foods and energy.^ While malnutrition is often associated with inadequate energy intake in developing countries, in wealthy, industrialized countries it is often a result of eating too much, or too little of some components of the diet.

 ^ Food composition tables ( see table) and food labels provide useful data for evaluating energy and nutrient intake of an individual diet.
  • human nutrition -- Britannica Online Encyclopedia 8 January 2010 5:19 UTC www.britannica.com [Source type: FILTERED WITH BAYES]

 ^ Shocking survey results have revealed that three-quarters of the city-dwelling population in the UK are suffering from low energy and waking up tired as a result of a high intake of stimulants such as tea, coffee, cigarettes and sugary foods.
  • Article List - PositiveHealth.com - United Kingdom 8 January 2010 5:19 UTC www.positivehealth.com [Source type: FILTERED WITH BAYES]

 .Both insulin and leptin normally function as satiety signals to the hypothalamus in the brain; however, insulin/leptin resistance may reduce this signal and therefore allow continued overfeeding despite large body fat stores.^ Even though the body usually protects against overdosing of most nutrients (especially water-soluble vitamins), excess vitamins A, D, and E are not automatically eliminated from the body because they are fat-soluble and therefore stored in body fat.

 ^ LDS is characterized by two types of changes in body fat distribution, which may occur alone or in combination.
  • HRSACareAction - Providing HIV/AIDS Care in a Changing Environment - August 2004 8 January 2010 5:19 UTC hab.hrsa.gov [Source type: Academic]

 ^ Weight Loss (decrease in both body cell mass and fat) .
  • Nutrition 8 January 2010 5:19 UTC aidsetc.org [Source type: Academic]

 .In addition, reduced leptin signalling to the brain may reduce leptin's normal effect to maintain an appropriately high metabolic rate.^ In addition, a significant loss of lean body mass, a notable slowing of the Basal Metabolic Rate (BMR) as well as, malnutrition, that in extreme cases may result in death, are typical side effects of such drastic dieting practices.

 ^ In addition, by helping clients adhere to appropriate food and medication schedules, providers can enhance the efficacy of medications and reduce the risk of drug resistance.
  • HRSACareAction - Providing HIV/AIDS Care in a Changing Environment - August 2004 8 January 2010 5:19 UTC hab.hrsa.gov [Source type: Academic]

 ^ There is evidence that the rate of fat metabolism may be accelerated by ingesting caffeine prior to and during endurance performance.
  • Nutrition for the Athlete 8 January 2010 5:19 UTC www.ext.colostate.edu [Source type: FILTERED WITH BAYES]
There is a debate about how and to what extent different dietary factors— such as intake of processed carbohydrates, total protein, fat, and carbohydrate intake, intake of saturated and trans fatty acids, and low intake of vitamins/minerals—contribute to the development of insulin and leptin resistance. In any case, analogous to the way modern man-made pollution may potentially overwhelm the environment's ability to maintain homeostasis, the recent explosive introduction of high glycemic index and processed foods into the human diet may potentially overwhelm the body's ability to maintain homeostasis and health (as evidenced by the metabolic syndrome epidemic).

Hyponatremia

Excess water intake, without replenishment of sodium and potassium salts, leads to hyponatremia, which can further lead to water intoxication at more dangerous levels. A well-publicized case occurred in 2007, when Jennifer Strange died while participating in a water-drinking contest.[44] More usually, the condition occurs in long-distance endurance events (such as marathon or triathlon competition and training) and causes gradual mental dulling, headache, drowsiness, weakness, and confusion; extreme cases may result in coma, convulsions, and death. The primary damage comes from swelling of the brain, caused by increased osmosis as blood salinity decreases. Effective fluid replacement techniques include Water aid stations during running/cycling races, trainers providing water during team games such as Soccer and devices such as Camel Baks which can provide water for a person without making it too hard to drink the water.

Antinutrient

Main article: Antinutrient
Antinutrients are natural or synthetic compounds that interfere with the absorption of nutrients. Nutrition studies focus on antinutrients commonly found in food sources and beverages.

Processed foods

Main article: Food processing
.Since the Industrial Revolution some two hundred years ago, the food processing industry has invented many technologies that both help keep foods fresh longer and alter the fresh state of food as they appear in nature.^ But I can say this, he has added so many items not normally available to this package that I am certain they won’t appear throughout the year.

 ^ Can the organization provide you with information regarding dropout rates, long term success rates, and could you meet with individuals that completed the program a year or two ago?

 ^ They also need to know how to prepare food safely—how to keep raw meat from contaminating foods that will not be cooked and how to make sure that foods are cooked to the appropriate temperature.
  • HRSACareAction - Providing HIV/AIDS Care in a Changing Environment - August 2004 8 January 2010 5:19 UTC hab.hrsa.gov [Source type: Academic]

 Cooling is the primary technology used to maintain freshness, whereas many more technologies have been invented to allow foods to last longer without becoming spoiled. These latter technologies include pasteurisation, autoclavation, drying, salting, and separation of various components, and all appear to alter the original nutritional contents of food. .Pasteurisation and autoclavation (heating techniques) have no doubt improved the safety of many common foods, preventing epidemics of bacterial infection.^ They lead to improved nutrition and physical growth, reduced susceptibility to common childhood infections and better resistance to cope with them.
  • Mother & Child Nutrition - Diarrhoea, Diarrhea, Dehydration, Oral Rehydration, Water, Sanitation, Hygiene - Rehydration Project 8 January 2010 5:19 UTC rehydrate.org [Source type: Academic]

 .But some of the (new) food processing technologies undoubtedly have downfalls as well.^ Some foods, particularly those that are highly processed and stimulating, elicit responses similar to addiction.
  • Raw Food Diet Lifestyle Information: Vibrance eZine: Living Nutrition Magazine: Natural Hygiene Books 8 January 2010 5:19 UTC www.livingnutrition.com [Source type: General]

 ^ Then you must not have heard about the “U.S. student sleuths use unique Cdn technology to identify mislabeled foods” report in the news.
Modern separation techniques such as milling, centrifugation, and pressing have enabled concentration of particular components of food, yielding flour, oils, juices and so on, and even separate fatty acids, amino acids, vitamins, and minerals. Inevitably, such large scale concentration changes the nutritional content of food, saving certain nutrients while removing others. .Heating techniques may also reduce food's content of many heat-labile nutrients such as certain vitamins and phytochemicals, and possibly other yet to be discovered substances.^ Offers advice that will help to promote health and reduce risk for chronic diseases such as heart disease, certain cancers, diabetes, stroke, and osteoporosis.
  • U.S. Government Bookstore: Browse by Subject: Nutrition 8 January 2010 5:19 UTC bookstore.gpo.gov [Source type: Academic]

 ^ Other dietary components such as DHA/EPA from fish oil, tocotrienols, vitamins B6 and B12, and quercetin contribute further to mitigating the inflammatory process.
  • Nutrition Section @ Chiro.Org 8 January 2010 5:19 UTC www.chiro.org [Source type: Academic]

 ^ And although scientists agree that there are a number of advantages, many also feel that, under certain circumstances, vegetarians may not be getting enough of a handful of nutrients.
  • Nutrition Section @ Chiro.Org 8 January 2010 5:19 UTC www.chiro.org [Source type: Academic]

 [45] .Because of reduced nutritional value, processed foods are often 'enriched' or 'fortified' with some of the most critical nutrients (usually certain vitamins) that were lost during processing.^ Some clients frequently eat cheap fast food from the corner carryout, unaware that their nutritional needs are not being met.
  • HRSACareAction - Providing HIV/AIDS Care in a Changing Environment - August 2004 8 January 2010 5:19 UTC hab.hrsa.gov [Source type: Academic]

 ^ Marion Nestle The debate over the nutritional value of organic foods isn't about health.
  • The Atlantic Food Channel: Nutrition 8 January 2010 5:19 UTC food.theatlantic.com [Source type: General]

 ^ Most clients need basic information not just on nutrition but also on food handling, for which Kopins provides guidelines both verbally and with handouts.
  • HRSACareAction - Providing HIV/AIDS Care in a Changing Environment - August 2004 8 January 2010 5:19 UTC hab.hrsa.gov [Source type: Academic]

 Nonetheless, processed foods tend to have an inferior nutritional profile compared to whole, fresh foods, regarding content of both sugar and high GI starches, potassium/sodium, vitamins, fiber, and of intact, unoxidized (essential) fatty acids. .In addition, processed foods often contain potentially harmful substances such as oxidized fats and trans fatty acids.^ Contains "down home" African American recipes which include foods that are lower in fat, saturated fat, cholesterol, and sodium.
  • U.S. Government Bookstore: Browse by Subject: Nutrition 8 January 2010 5:19 UTC bookstore.gpo.gov [Source type: Academic]
A dramatic example of the effect of food processing on a population's health is the history of epidemics of beri-beri in people subsisting on polished rice. Removing the outer layer of rice by polishing it removes with it the essential vitamin thiamine, causing beri-beri. Another example is the development of scurvy among infants in the late 1800s in the United States. It turned out that the vast majority of sufferers were being fed milk that had been heat-treated (as suggested by Pasteur) to control bacterial disease. Pasteurisation was effective against bacteria, but it destroyed the vitamin C.
.As mentioned, lifestyle- and obesity-related diseases are becoming increasingly prevalent all around the world.^ Obesity and other nutrition-related chronic diseases .
  • Mother & Child Nutrition - Diarrhoea, Diarrhea, Dehydration, Oral Rehydration, Water, Sanitation, Hygiene - Rehydration Project 8 January 2010 5:19 UTC rehydrate.org [Source type: Academic]

 ^ The Leading Causes of Death The leading causes of death are all lifestyle related and often preventable.
  • Nutrition Section @ Chiro.Org 8 January 2010 5:19 UTC www.chiro.org [Source type: Academic]

 ^ It is also a timely period to shape and consolidate healthy eating and lifestyle behaviours, thereby preventing or postponing the onset of nutrition-related chronic diseases in adulthood.
  • Mother & Child Nutrition - Diarrhoea, Diarrhea, Dehydration, Oral Rehydration, Water, Sanitation, Hygiene - Rehydration Project 8 January 2010 5:19 UTC rehydrate.org [Source type: Academic]

 .There is little doubt that the increasingly widespread application of some modern food processing technologies has contributed to this development.^ Some foods, particularly those that are highly processed and stimulating, elicit responses similar to addiction.
  • Raw Food Diet Lifestyle Information: Vibrance eZine: Living Nutrition Magazine: Natural Hygiene Books 8 January 2010 5:19 UTC www.livingnutrition.com [Source type: General]

 ^ Not only must the borrow area contain enough sediment with the appropriate properties for nourishment, but there are some materials that cannot be included in the dredge and construction process.
  • Beach Nourishment - Coastal Geology 20 November 2009 10:16 UTC www.csc.noaa.gov [Source type: Academic]

 ^ There are 100's of brands of food supplements on the market, but let's look at some quality issues.
  • Nutrition Section @ Chiro.Org 8 January 2010 5:19 UTC www.chiro.org [Source type: Academic]

 .The food processing industry is a major part of modern economy, and as such it is influential in political decisions (e.g.^ Discovering antibiotics in the 1930s was a major breakthrough for modern medicine as it allowed many people to be saved from life threatening diseases such as typhoid and meningitis.
  • Article List - PositiveHealth.com - United Kingdom 8 January 2010 5:19 UTC www.positivehealth.com [Source type: FILTERED WITH BAYES]

 nutritional recommendations, agricultural subsidising). .In any known profit-driven economy, health considerations are hardly a priority; effective production of cheap foods with a long shelf-life is more the trend.^ As a child, I suffered no serious or long-term health conditions and had regular access to an abundance of "good nourishing food".
  • Raw Food Diet Lifestyle Information: Vibrance eZine: Living Nutrition Magazine: Natural Hygiene Books 8 January 2010 5:19 UTC www.livingnutrition.com [Source type: General]

 ^ Presents the best information available to assist in making wise and nutritious food choices to sustain life and good health.
  • U.S. Government Bookstore: Browse by Subject: Nutrition 8 January 2010 5:19 UTC bookstore.gpo.gov [Source type: Academic]

 ^ Regular exercise, a healthy diet, and a proactive approach to physical, mental, emotional and spiritual wellness are the cornerstones for the foundation of life-long health.
  • Nutrition - Find great deals, lowest prices, and buy Nutrition at Shopping.com 8 January 2010 5:19 UTC www.shopping.com [Source type: General]

 .In general, whole, fresh foods have a relatively short shelf-life and are less profitable to produce and sell than are more processed foods.^ I know personally I am happier and leaner when enjoying life and keeping a leaner body then when I start to increase the girth a little more than comfortable normal.

 ^ Just be more active, move, walk, run, play… do something different, something more than you do today and do it again and again and enjoy the process, great things will come of it.

 ^ Generally, beach sands are fairly well-sorted but might also have a second mode that ranges in relative proportion up to more than 50 percent of the sediment.
  • Beach Nourishment - Coastal Geology 20 November 2009 10:16 UTC www.csc.noaa.gov [Source type: Academic]

 Thus the consumer is left with the choice between more expensive but nutritionally superior whole, fresh foods, and cheap, usually nutritionally inferior processed foods. .Because processed foods are often cheaper, more convenient (in both purchasing, storage, and preparation), and more available, the consumption of nutritionally inferior foods has been increasing throughout the world along with many nutrition-related health complications.^ But I can say this, he has added so many items not normally available to this package that I am certain they won’t appear throughout the year.

 ^ Vibrance contains the best nutrition and health information content of any magazine in the world.” -Dr.
  • Raw Food Diet Lifestyle Information: Vibrance eZine: Living Nutrition Magazine: Natural Hygiene Books 8 January 2010 5:19 UTC www.livingnutrition.com [Source type: General]

 ^ Nutrition interventions should address challenges associated with new, complex antiretroviral regimens, which involve many pills; have complicated dosing schedules; and may cause symptoms that negatively affect food intake, absorption, and nutrition status.
  • HRSACareAction - Providing HIV/AIDS Care in a Changing Environment - August 2004 8 January 2010 5:19 UTC hab.hrsa.gov [Source type: Academic]

History

Humans have evolved as omnivorous hunter-gatherers over the past 250,000 years. .The diet of early modern humans varied significantly depending on location and climate.^ Human Nutrition This course provides an overview of nutrition and the components of a nutritious diet during the various stages of the life cycle.
  • Certificate Program in Nutrition 8 January 2010 5:19 UTC continuinged.uml.edu [Source type: Academic]

 .The diet in the tropics tended to be based more heavily on plant foods, while the diet at higher latitudes tended more towards animal products.^ Eating a plant-based diet is healthiest.
  • Healthy Eating Pyramid - What Should You Eat? - The Nutrition Source - Harvard School of Public Health 8 January 2010 5:19 UTC www.hsph.harvard.edu [Source type: News]

 ^ Soy Proteins and Diet Vegetarians and health enthusiasts have known for years that foods rich in soy protein offer a good alternative to meat, poultry, and other animal-based products.
  • Nutrition Guide for your Child at Keep Kids Healthy 8 January 2010 5:19 UTC www.keepkidshealthy.com [Source type: General]

 ^ Diets are rarely maintainable through food alone and extra factors like work and working out only make it more difficult.
  • Nutrition | Right Vita - Your Online Vitamin Resource 20 September 2009 18:27 UTC www.rightvita.com [Source type: FILTERED WITH BAYES]

 Analysis of postcranial and cranial remains of humans and animals from the Neolithic, along with detailed bone modification studies have shown that cannibalism was also prevalent among prehistoric humans.[46]
Agriculture developed about 10,000 years ago in multiple locations throughout the world, providing grains such as wheat, rice, potatoes, and maize, with staples such as bread, pasta, and tortillas. Farming also provided milk and dairy products, and sharply increased the availability of meats and the diversity of vegetables. The importance of food purity was recognized when bulk storage led to infestation and contamination risks. Cooking developed as an often ritualistic activity, due to efficiency and reliability concerns requiring adherence to strict recipes and procedures, and in response to demands for food purity and consistency.[47]

From antiquity to 1900

The first recorded nutritional experiment is found in the Bible's Book of Daniel. Daniel and his friends were captured by the king of Babylon during an invasion of Israel. Selected as court servants, they were to share in the king's fine foods and wine. But they objected, preferring vegetables (pulses) and water in accordance with their Jewish dietary restrictions. The king's chief steward reluctantly agreed to a trial. Daniel and his friends received their diet for 10 days and were then compared to the king's men. Appearing healthier, they were allowed to continue with their diet.[48]
Anaxagoras
Around 475 BC, Anaxagoras stated that food is absorbed by the human body and therefore contained "homeomerics" (generative components), suggesting the existence of nutrients.[47] Around 400 BC, Hippocrates said, "Let food be your medicine and medicine be your food."[49]
In the 1500s, scientist and artist Leonardo da Vinci compared metabolism to a burning candle. In 1747, Dr. James Lind, a physician in the British navy, performed the first scientific nutrition experiment, discovering that lime juice saved sailors who had been at sea for years from scurvy, a deadly and painful bleeding disorder. The discovery was ignored for forty years, after which British sailors became known as "limeys." The essential vitamin C within lime juice would not be identified by scientists until the 1930s.
Around 1770, Antoine Lavoisier, the "Father of Nutrition and Chemistry" discovered the details of metabolism, demonstrating that the oxidation of food is the source of body heat. In 1790, George Fordyce recognized calcium as necessary for fowl survival. In the early 1800s, the elements carbon, nitrogen, hydrogen and oxygen were recognized as the primary components of food, and methods to measure their proportions were developed.
In 1816, François Magendie discovered that dogs fed only carbohydrates and fat lost their body protein and died in a few weeks, but dogs also fed protein survived, identifying protein as an essential dietary component. In 1840, Justus Liebig discovered the chemical makeup of carbohydrates (sugars), fats (fatty acids) and proteins (amino acids.) In the 1860s, Claude Bernard discovered that body fat can be synthesized from carbohydrate and protein, showing that the energy in blood glucose can be stored as fat or as glycogen.
In the early 1880s, Kanehiro Takaki observed that Japanese sailors (whose diets consisted almost entirely of white rice) developed beriberi (or endemic neuritis, a disease causing heart problems and paralysis) but British sailors and Japanese naval officers did not. Adding various types of vegetables and meats to the diets of Japanese sailors prevented the disease.
In 1896, Baumann observed iodine in thyroid glands. In 1897, Christiaan Eijkman worked with natives of Java, who also suffered from beriberi. .Eijkman observed that chickens fed the native diet of white rice developed the symptoms of beriberi, but remained healthy when fed unprocessed brown rice with the outer bran intact.^ Opt for whole grain nutrition (brown rice, whole wheat bread, rolled oats, barley, millet), not refined "white" products, such as white bread, white rice, or products made with white flour.
  • Nutrition for Seniors: Healthy Eating Tips for Older Adults 8 January 2010 5:19 UTC www.helpguide.org [Source type: General]

 ^ The author looks at milk and why, like other white dietary products – salt, sugar, white flour, white rice, and white pasta – it should be excluded from our diet.
  • Article List - PositiveHealth.com - United Kingdom 8 January 2010 5:19 UTC www.positivehealth.com [Source type: FILTERED WITH BAYES]

 ^ Chelonians that are fed a diet too high in protein and other nutrients may develop shell abnormalities that will affect them for life.
  • Nutrition of Turtles and Tortoises 8 January 2010 5:19 UTC www.exoticpetvet.net [Source type: FILTERED WITH BAYES]

 Eijkman cured the natives by feeding them brown rice, discovering that food can cure disease. Over two decades later, nutritionists learned that the outer rice bran contains vitamin B1, also known as thiamine.

From 1900 to the present

In the early 1900s, Carl Von Voit and Max Rubner independently measured caloric energy expenditure in different species of animals, applying principles of physics in nutrition. In 1906, Wilcock and Hopkins showed that the amino acid tryptophan was necessary for the survival of rats. He fed them a special mixture of food containing all the nutrients he believed were essential for survival, but the rats died. A second group of rats to which he also fed fed an amount of milk containing vitamins.[50] Gowland Hopkins recognized "accessory food factors" other than calories, protein and minerals, as organic materials essential to health but which the body cannot synthesize. In 1907, Stephen M. Babcock and Edwin B. Hart conducted the single-grain experiment. This experiment runs through 1911.
In 1912, Casimir Funk coined the term vitamin, a vital factor in the diet, from the words "vital" and "amine," because these unknown substances preventing scurvy, beriberi, and pellagra, were thought then to be derived from ammonia. The vitamins were studied in the first half of the twentieth century.
In 1913, Elmer McCollum discovered the first vitamins, fat soluble vitamin A, and water soluble vitamin B (in 1915; now known to be a complex of several water-soluble vitamins) and names vitamin C as the then-unknown substance preventing scurvy. Lafayette Mendel and Thomas Osborne also perform pioneering work on vitamin A and B. In 1919, Sir Edward Mellanby incorrectly identified rickets as a vitamin A deficiency, because he could cure it in dogs with cod liver oil.[51] In 1922, McCollum destroyed the vitamin A in cod liver oil but finds it still cures rickets, naming vitamin D Also in 1922, H.M. Evans and L.S. Bishop discover vitamin E as essential for rat pregnancy, originally calling it "food factor X" until 1925.
In 1925, Hart discovered that trace amounts of copper are necessary for iron absorption. In 1927, Adolf Otto Reinhold Windaus synthesized vitamin D, for which he won the Nobel Prize in Chemistry in 1928. In 1928, Albert Szent-Györgyi isolated ascorbic acid, and in 1932 proves that it is vitamin C by preventing scurvy. In 1935 he synthesizes it, and in 1937 he wins a Nobel Prize for his efforts. Szent-Györgyi concurrently elucidates much of the citric acid cycle.
In the 1930s, William Cumming Rose identified essential amino acids, necessary protein components which the body cannot synthesize. In 1935, Underwood and Marston independently discover the necessity of cobalt. In 1936, Eugene Floyd Dubois showed that work and school performance are related to caloric intake. In 1938, Erhard Fernholz discovered the chemical structure of vitamin E. It was synthesised by Paul Karrer.
In 1940, rationing in the United Kingdom during and after World War II took place according to nutritional principles drawn up by Elsie Widdowson and others. In 1941, the first Recommended Dietary Allowances (RDAs) were established by the National Research Council.
In 1992, The U.S. Department of Agriculture introduced the Food Guide Pyramid. In 2002, a Natural Justice study showed a relation between nutrition and violent behavior. In 2005, a study found that obesity may be caused by adenovirus in addition to bad nutrition.[52]

Plant Nutrition

Main article: Plant nutrition
Plant nutrition is the study of the chemical elements that are necessary for plant growth. There are several principles that apply to plant nutrition. Some elements are directly involved in plant metabolism. However, this principle does not account for the so-called beneficial elements, whose presence, while not required, has clear positive effects on plant growth.
A nutrient that is able to limit plant growth according to Liebig's law of the minimum, is considered an essential plant nutrient if the plant can not complete its full life cycle without it. There are 17 essential plant nutrients.
Macronutrients:
Micronutrients (trace levels) include:

Macronutrients

Calcium
Calcium regulates transport of other nutrients into the plant and is also involved in the activation of certain plant enzymes. Calcium deficiency results in stunting.
Nitrogen
Nitrogen is an essential component of all proteins. Nitrogen deficiency most often results in stunted growth.
Phosphorus
Phosphorus is important in plant bioenergetics. As a component of ATP, phosphorus is needed for the conversion of light energy to chemical energy (ATP) during photosynthesis. Phosphorus can also be used to modify the activity of various enzymes by phosphorylation, and can be used for cell signalling. Since ATP can be used for the biosynthesis of many plant biomolecules, phosphorus is important for plant growth and flower/seed formation.
Potassium
Potassium regulates the opening and closing of the stoma by a potassium ion pump. Since stomata are important in water regulation, potassium reduces water loss from the leaves and increases drought tolerance. Potassium deficiency may cause necrosis or interveinal chlorosis.
Silicon
Silicon is deposited in cell walls and contributes to its mechanical properties including rigidity and elasticity

Micronutrients

Boron
Boron is important in sugar transport, cell division, and synthesizing certain enzymes. Boron deficiency causes necrosis in young leaves and stunting.
Copper
Copper is important for photosynthesis. Symptoms for copper deficiency include chlorosis. Involved in many enzyme processes. Necessary for proper photosythesis. Involved in the manufacture of lignin (cell walls). Involved in grain production.
Chlorine
Chlorine is necessary for osmosis and ionic balance; it also plays a role in photosynthesis.
Iron
Iron is necessary for photosynthesis and is present as an enzyme cofactor in plants. Iron deficiency can result in interveinal chlorosis and necrosis.
Manganese
Manganese is necessary for building the chloroplasts. Manganese deficiency may result in coloration abnormalities, such as discolored spots on the foliage.
Molybdenum
Molybdenum is a cofactor to enzymes important in building amino acids.
Nickel
In higher plants, Nickel is essential for activation of urease, an enzyme involved with nitrogen metabolism that is required to process urea. Without Nickel, toxic levels of urea accumulate, leading to the formation of necrotic lesions. In lower plants, Nickel activates several enzymes involved in a variety of processes, and can substitute for Zinc and Iron as a cofactor in some enzymes.[citation needed]
Sodium
Sodium is involved in the regeneration of phosphoenolpyruvate in CAM and C4 plants. It can also substitute for potassium in some circumstances.
Zinc
Zinc is required in a large number of enzymes and plays an essential role in DNA transcription. A typical symptom of zinc deficiency is the stunted growth of leaves, commonly known as "little leaf" and is caused by the oxidative degradation of the growth hormone auxin.

Processes

Plants uptake essential elements from the soil through their roots and from the air (mainly consisting of nitrogen and oxygen) through their leaves. Nutrient uptake in the soil is achieved by cation exchange, wherein root hairs pump hydrogen ions (H+) into the soil through proton pumps. These hydrogen ions displace cations attached to negatively charged soil particles so that the cations are available for uptake by the root. In the leaves, stomata open to take in carbon dioxide and expel oxygen. The carbon dioxide molecules are used as the carbon source in photosynthesis.
Though nitrogen is plentiful in the Earth's atmosphere, relatively few plants engage in nitrogen fixation (conversion of atmospheric nitrogen to a biologically useful form). Most plants therefore require nitrogen compounds to be present in the soil in which they grow.
Plant nutrition is a difficult subject to understand completely, partially because of the variation between different plants and even between different species or individuals of a given clone. Elements present at low levels may cause deficiency symptoms, and toxicity is possible at levels that are too high. Further, deficiency of one element may present as symptoms of toxicity from another element, and vice-versa.
Carbon and oxygen are absorbed from the air, while other nutrients are absorbed from the soil. Green plants obtain their carbohydrate supply from the carbon dioxide in the air by the process of photosynthesis.

Malnutrition

Main article: Malnutrition
Malnutrition refers to insufficient, excessive, or imbalanced consumption of nutrients by an organism. In developed countries, the diseases of malnutrition are most often associated with nutritional imbalances or excessive consumption.
Although there are more organisms in the world who are malnourished due to insufficient consumption, increasingly more organisms suffer from excessive over-nutrition; a problem caused by an over abundance of sustenance coupled with the instinctual desire (by animals in particular) to consume all that it can

Insufficient

Under consumption generally refers to the long-term consumption of insufficient sustenance in relation to the energy that an organism expends or expels, leading to poor health.

Excessive

Over consumption generally refers to the long-term consumption of excess sustenance in relation to the energy that an organism expends or expels, leading to poor health and in animals obesity. It can cause excessive hair loss, brittle nails, and irregular premenstrual cycles for females

Unbalanced

When too much of one or more nutrients is present in the diet to the exclusion of the proper amount of other nutrients, the diet is said to be unbalanced.

See also

Food portal
Main article: Outline of nutrition
Balanced Eating:
Biology:
Dangers of poor nutrition
Food (portal)
Lists:
Profession:
Tools:
Organizations:
Related topics
Main article: Health

Further reading

  • Curley, S., and Mark (1990). The Natural Guide to Good Health, Lafayette, Louisiana, Supreme Publishing
  • Galdston, I. (1960). Human Nutrition Historic and Scientific. New York: International Universities Press. 
  • Mahan, L.K. and Escott-Stump, S. eds. (2000). Krause's Food, Nutrition, and Diet Therapy (10th ed.). Philadelphia: W.B. Saunders Harcourt Brace. ISBN 0-7216-7904-8. 
  • Thiollet, J.-P. (2001). Vitamines & minéraux. Paris: Anagramme. 
  • Walter C. Willett and Meir J. Stampfer (January 2003). "Rebuilding the Food Pyramid". Scientific American 288 (1): 64–71. doi:10.1038/scientificamerican0103-64. PMID 12506426. 

References

  1. ^ "Making the Transition to Whole Foods"
  2. ^ Berg J, Tymoczko JL, Stryer L (2002). Biochemistry (5th ed.). San Francisco: W.H. Freeman. p. 603. ISBN 0-7167-4684-0. 
  3. ^ Cite error: Invalid <ref> tag; no text was provided for refs named http:.2F.2Fwww.mayoclinic.com.2Fhealth.2Ffiber.2FNU00033; see Help:Cite error.
  4. ^ Nelson, D. L.; Cox, M. M. (2000). Lehninger Principles of Biochemistry (3rd ed.). New York: Worth Publishing. ISBN 1-57259-153-6. 
  5. ^ D. E. C. Corbridge (1995). Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology (5th ed.). Amsterdam: Elsevier. ISBN 0-444-89307-5. 
  6. ^ Lippard, S. J. and Berg, J. M. (1994). Principles of Bioinorganic Chemistry. Mill Valley, CA: University Science Books. 
  7. ^ Shils et al. (2005). Modern Nutrition in Health and Disease. Lippincott Williams and Wilkins. ISBN 0-7817-4133-5. 
  8. ^ "Healthy Water Living". http://www.bbc.co.uk/health/healthy_living/nutrition/drinks_water.shtml. Retrieved 2007-02-01. 
  9. ^ "Drink at least eight glasses of water a day." Really? Is there scientific evidence for "8 × 8"? by Heinz Valdin, Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire
  10. ^ Drinking Water - How Much?, Factsmart.org web site and references within
  11. ^ Food and Nutrition Board, National Academy of Sciences. Recommended Dietary Allowances, revised 1945. National Research Council, Reprint and Circular Series, No. 122, 1945 (Aug), p. 3-18.
  12. ^ Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate, Food and Nutrition Board
  13. ^ "Water: How much should you drink every day? - MayoClinic.com". MayoClinic.com<!. http://www.mayoclinic.com/health/water/NU00283. Retrieved 2009-05-21. 
  14. ^ Bjelakovic G; Nikolova, D; Gluud, LL; Simonetti, RG; Gluud, C (2007). "Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis". JAMA 297 (8): 842–57. doi:10.1001/jama.297.8.842. PMID 17327526. 
  15. ^ Seddon JM, Ajani UA, Sperduto RD, et al. (November 1994). "Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration. Eye Disease Case-Control Study Group". JAMA 272 (18): 1413–20. doi:10.1001/jama.272.18.1413. PMID 7933422.  See http://www.mdsupport.org/library/zeaxanthin.html.
  16. ^ Lyle BJ, Mares-Perlman JA, Klein BE, Klein R, Greger JL (May 1999). "Antioxidant intake and risk of incident age-related nuclear cataracts in the Beaver Dam Eye Study". Am. J. Epidemiol. 149 (9): 801–9. PMID 10221316. 
    Yeum KJ, Taylor A, Tang G, Russell RM (December 1995). "Measurement of carotenoids, retinoids, and tocopherols in human lenses". Invest. Ophthalmol. Vis. Sci. 36 (13): 2756–61. PMID 7499098. 
    Chasan-Taber L, Willett WC, Seddon JM, et al. (October 1999). "A prospective study of carotenoid and vitamin A intakes and risk of cataract extraction in US women". Am. J. Clin. Nutr. 70 (4): 509–16. PMID 10500020. 
    Brown L, Rimm EB, Seddon JM, et al. (October 1999). "A prospective study of carotenoid intake and risk of cataract extraction in US men". Am. J. Clin. Nutr. 70 (4): 517–24. PMID 10500021. 
  17. ^ Pattison DJ, Symmons DP, Lunt M, et al. (August 2005). "Dietary beta-cryptoxanthin and inflammatory polyarthritis: results from a population-based prospective study". Am. J. Clin. Nutr. 82 (2): 451–5. PMID 16087992. 
    Am J Epidemiology 2006 163(1).
  18. ^ Handelman GJ, Nightingale ZD, Lichtenstein AH, Schaefer EJ, Blumberg JB (August 1999). "Lutein and zeaxanthin concentrations in plasma after dietary supplementation with egg yolk". Am. J. Clin. Nutr. 70 (2): 247–51. PMID 10426702. 
  19. ^ Note that some isoflavone studies have linked isoflavones to increased cancer risk.
  20. ^ Monoterpenes are enormously widespread among green plant life (including algae). Many plants, notably coniferous trees, emit beneficial monoterpenes into the atmosphere.
  21. ^ http://www.mypyramid.gov/downloads/sample_menu.pdf
  22. ^ Commission on Life Sciences. (1985). Nutrition Education in US Medical Schools, p. 4. National Academies Press.
  23. ^ Adams KM, Lindell KC, Kohlmeier M, Zeisel SH (April 2006). "Status of nutrition education in medical schools". Am. J. Clin. Nutr. 83 (4): 941S–4S. PMID 16600952. 
  24. ^ a b Campbell T., Campbell T. (2005). The China Study. Dallas: Benella Books. 
  25. ^ Eckel RH, Borra S, Lichtenstein AH, Yin-Piazza SY (April 2007). "Understanding the complexity of trans fatty acid reduction in the American diet: American Heart Association Trans Fat Conference 2006: report of the Trans Fat Conference Planning Group". Circulation 115 (16): 2231–46. doi:10.1161/CIRCULATIONAHA.106.181947. PMID 17426064. http://circ.ahajournals.org/cgi/reprint/115/16/2231. 
  26. ^ Ducimetière P, Lang T, Amouyel P, Arveiler D, Ferrières J (January 2000). "Why mortality from heart disease is low in France. Rates of coronary events are similar in France and Southern Europe". BMJ 320 (7229): 249–50. doi:10.1136/bmj.320.7229.249/a (inactive 2010-03-17). PMID 10642245. PMC 1117444. http://www.bmj.com/cgi/content/full/320/7229/249/a. 
  27. ^ Di Pasquale, Mauro G. (2008). "Utilization of Proteins in Energy Metabolism". in Ira Wolinsky, Judy A. Driskell. Sports Nutrition: Energy metabolism and exercise. CRC Press. p. 73. ISBN 978-0-8493-7950-5. 
  28. ^ Di Pasquale, Mauro G. (2008). "Utilization of Proteins in Energy Metabolism". in Ira Wolinsky, Judy A. Driskell. Sports Nutrition: Energy metabolism and exercise. CRC Press. p. 79. ISBN 978-0-8493-7950-5. 
  29. ^ http://www.winforum.org/GamePlan-bw.pdf. page 19
  30. ^ William D. McArdle, Frank I. Katch, Victor L. Katch (2006). Exercise Physiology: Energy, Nutrition, and Human Performance. Lippincott Williams & Wilkins. 
  31. ^ "Nutrition — Healthy eating: Bread, cereals and other starchy foods". BBC. July 2008. http://www.bbc.co.uk/health/healthy_living/nutrition/basics_carbos.shtml. Retrieved 2008-11-09. 
  32. ^ Jere R. Behrman (1996). "The impact of health and nutrition on education". World Bank Research Observer 11 (1): 23–37. 
  33. ^ a b American College Health Association (2007). "American College Health Association National College Health Assessment Spring 2006 Reference Group data report (abridged)". J Am Coll Health 55 (4): 195–206. doi:10.3200/JACH.55.4.195-206. PMID 17319325. 
  34. ^ Benton D, Sargent J (July 1992). "Breakfast, blood glucose and memory". Biol Psychol 33 (2-3): 207–10. doi:10.1016/0301-0511(92)90032-P. PMID 1525295. 
  35. ^ Kanarek RB, Swinney D (February 1990). "Effects of food snacks on cognitive performance in male college students". Appetite 14 (1): 15–27. doi:10.1016/0195-6663(90)90051-9. PMID 2310175. 
  36. ^ Whitley JR, O'Dell BL, Hogan AG (September 1951). "Effect of diet on maze learning in second generation rats; folic acid deficiency". J. Nutr. 45 (1): 153–60. PMID 14880969. 
  37. ^ Umezawa M, Kogishi K, Tojo H, et al. (February 1999). "High-linoleate and high-alpha-linolenate diets affect learning ability and natural behavior in SAMR1 mice". J. Nutr. 129 (2): 431–7. PMID 10024623. 
  38. ^ Glewwe P, Jacoby H, King E (2001). "Early childhood nutrition and academic achievement: A longitudinal analysis". Journal of Public Economics 81 (3): 345–68. doi:10.1016/S0047-2727(00)00118-3. 
  39. ^ Managed food service contractors react quickly to the demands of their clients achievement: A longitudinal analysis. Journal of Public Economics, 81(3), 345-368.
  40. ^ Guernsey L (1993). "Many colleges clear their tables of steak, substitute fruit and pasta". Chronicle of Higher Education 39 (26): A30. 
  41. ^ Duster T, Waters A (2006). "Engaged learning across the curriculum: The vertical integration of food for thought". Liberal Education 92 (2): 42. 
  42. ^ Lakhan SE, Vieira KF (2008). "Nutritional therapies for mental disorders". Nutr J 7: 2. doi:10.1186/1475-2891-7-2. PMID 18208598. PMC 2248201. http://www.nutritionj.com/content/7/1/2. 
  43. ^ Coren, Michael (2005-03-10). "Study: Cancer no longer rare in poorer countries". CNN. http://www.cnn.com/2005/HEALTH/03/09/cancer.study/index.html. Retrieved 2007-01-01. 
  44. ^ "Why is too much water dangerous?". BBC News. 2007-01-15. http://news.bbc.co.uk/1/hi/magazine/6263029.stm. Retrieved 2008-11-09. 
  45. ^ Morris, Audrey; Audia Barnett, Olive-Jean Burrows (2004). "Effect of Processing on Nutrient Content of Foods" (PDF). Cajanus 37 (3): 160–164. http://www.paho.org/English/CFNI/cfni-caj37No304-art-3.pdf. Retrieved 2006-10-26. 
  46. ^ Villa P, Bouville C, Courtin J, et al. (July 1986). "Cannibalism in the Neolithic". Science 233 (4762): 431–7. doi:10.1126/science.233.4762.431. PMID 17794567. 
  47. ^ a b History of the Study of Nutrition in Western Culture (Rai University lecture notes for General Nutrition course, 2004)
  48. ^ Daniel 1:5-16 (alternative translation)
  49. ^ Richard Smith (24 January 2004). "Let food by thy medicine…". BMJ 328: 0-g. doi:10.1136/bmj.328.7433.0-g. http://bmj.bmjjournals.com/cgi/content/full/328/7433/0-g. Retrieved 2008-11-09. 
  50. ^ Heinemann 2e Biology Activity Manual by Judith Brotherton and Kate Mundie
  51. ^ Unraveling the Enigma of Vitamin D - a paper funded by the United States National Academy of Sciences
  52. ^ "Can a virus make you fat?" at BBC News; "Contagious obesity? Identifying the human adenoviruses that may make us fat" at Science Blog

External links

Databases and search engines

Food science
Allied health professions
Public health
General
Preventive
medicine
Population
health
History of medicine
Basic sciences
History of anatomy • History of biochemistry • History of biostatistics • History of cytology • History of diagnosis • History of embriology • History of epidemiology • History of genetics • History of histology • History of immunology • History of medical physics • History of microbiology • History of neuroscience • History of nutrition • History of pathology as a science • History of pharmacology • History of physiology • History of toxicology
 Treatment of a skull injury
Medical specialties
History of anesthesiology • History of cardiology • History of cardiovascular surgery • History of clinical laboratory sciences • History of clinical neurophysiology • History of dermatology • History of emergency medicine • History of endocrinology • History of gastroenterology • History of general surgery • History of geriatrics • History of hematology • History of hepatology • History of infectious diseases • History of intensive care medicine • History of internal medicine • History of invasive and interventional cardiology • History of maxillofacial surgery • History of nephrology • History of neurology • History of neurosurgery • History of obstetrics and gynaecology • History of oncology • History of ophthalmology • History of orthopedic surgery • History of otolaryngology • History of paliative care • History of pathology as a medical specialty • History of physical medicne and rehabilitation • History of plastic surgery • History of proctology • Timeline of psychiatry • History of pulmonology • History of radiology • History of rheumatology • History of surgery • History of surgical oncology • History of thoracic surgery • History of transplant surgery • History of trauma surgery • History of urology • History of vascular surgery

Study guide

Up to date as of January 14, 2010

From Wikiversity

Eat the rainbow
Lesson of The digestive system
Every being needs to absorb some energy in order to develop itself. The alimentary adaptation to satisfy physiological needs is called dietetic. It makes intervene some nutriments from different natures in variable quantities. Some are fresh and need to be conserved in the fridge at +4°C.

Food Guide Recommendations

  1. The energy contribution of main nutrients is :
    1g of carbohydrate gives 4kcal or 17kJ.
    1g of protein gives 4kcal or 17kJ.
    1g of lipid gives 9kcal or 38kJ.
    1g alcohol gives 7kcal or 29kJ.
  2. The ideal repartition of the brought energy by aliments is :
    55% of carbohydrate (including 2/3 of complex ones)
    30% of protein (including 1/2 from a vegetarian origin)
    15% of lipid (including 1/2 from a vegetarian origin)
  3. Moreover, which should drink least 2l of water as much as necessary, more than 25 % comes from the solids ingested aliments, which should be preferably cooked and carefully munch in order to facilitate digestion. Because the satiety from the stomach to the brain takes 15 to 20 minutes, to eat fast makes eat more.
  4. Between 2 to 6g of salt per day.
  5. Nature of nutrients :
CANADA
FRANCE
Food Group Servings per day Choose more often Food Group Servings per day Choose more often
Grain products 5-12 whole grain and enriched grain products Starchy food Every meal
Vegetables and fruit 5-10 dark green and orange vegetables and orange fruit Vegetables and fruit > 5 (≈ 500g) Excluding yoghurts, fruit biscuits and juice
Dairy 2-4 Lower fat dairy products Dairy 3
Meat and alternatives 2-3 lean meat, poultry, fish, peas, beans, lentils Meat and alternatives 1-2 meat, fishing products and eggs

Cardiovascular Disease Prevention

Food Item Recommendations Effects
Fat fat intake < 30% total energy
saturated fat < 10% of energy cholesterol < 300mg/d limit trans fatty acids
 lower LDL
Omega 3 fatty acid rich foods > 2 servings / week of fish or omega rich plants (ie. flaxseed, canola oil, soybean oil, nuts) decreased: sudden death, arrhythmia, blood-clots, hypertriglyceridemia
Salt < 6g/day lower BP
Alcohol < 2 drinks/day men (around 30cl of wine)
< 1 drink/day women
 lower BP

The nutritional content children are getting is a serious problem in America. Improving children’s nutrition will help decrease the leading causes of death and improve the most important determinants of health. Research suggests that not having breakfast can affect a child’s intellectual performance. Considering this, nearly 80% of students do not eat fruits and vegetables 5 or more times per day. Also, the prevalence of overweight among children aged 6 to 11 more than doubled in the past 20 years, going from 7% in 1980 to 18% in 2004. 61% of overweight young people have at least one additional risk factor for heart disease, such as high cholesterol or high blood pressure. Children who are overweight are also at greater risk for the following problems: bone and joint problems, sleep apnea, social and psychological problems, poor self-esteem, more likely to become overweight or obese adult, type 2 diabetes, stroke, several types of cancer, and osteoarthritis. These are some shocking results that are affecting children everyday. Healthy lifestyle habits, including healthy eating and physical activity, can lower the risk of becoming overweight and developing these related diseases.
One way to make sure your child is getting the nutrition he/she needs is to make sure they eat the rainbow :
  1. Red- Bell peppers, Cherries, Watermelon, Strawberries, Beets, Radishes
  2. Orange- Apricots, Cantaloupe, Mango, Carrots, Peaches, Sweet potatoes
  3. Yellow- Bananas, Pineapple, Squash, Star fruit, Yellow onion
  4. Green- Asparagus, Broccoli, Honeydew melon, Spinach, Kiwi, Peas
  5. Blue/Purple- Blackberries, Eggplant, Figs, Plums, Raisins, Grapes

References

Toronto Notes 2005
The Canada Food Guide is for those > age 2
http://www.cdc.gov/HealthyYouth/overweight/index.htm
http://www.bjcschooloutreach.org
(fr) http://mangerbouger.fr
Family Medicine (LMCC)

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

.NUTRITION. The physiology of nutrition involves the study of the way in which the tissues of the body, and more especially the great master tissues, muscle and nerve, obtain the material for growth and repair and the energy for mechanical work and heat production, and of the mode in which they get rid of the waste products of their activity.^ This is one way to allow me to continually research and develop more great products that will help you achieve your fat loss and muscle building transformation goals.

 ^ Tags: Building Muscle challenge coaching Energy exercise fat loss Interview lean bodies Metabolic Surge muscle building Nick Nilsson nutrition Questions supplements transformation challenge workouts .

 ^ If you are already active, be more active and you won’t need to adjust your calories, just your activities will increase a lean body lifestyle.

 The study is therefore very largely a study of the history of the food of the body, since it is in the food that the necessary matter and energy are supplied. .Under Dietetics the composition and special importance of various foods and the laws which regulate the supply of food under different conditions of the body are separately dealt with.^ Variation in serving sizes, preparation techniques, product testing and sources of supply, as well as regional and seasonal differences may affect the nutrition values for each product.
  • McDonald's USA - McDonald's Nutrition Facts 8 January 2010 5:19 UTC nutrition.mcdonalds.com [Source type: General]

 .Here the mode of digestion, the utilization and the elimination of the end products of the three great constituents, proteins, carbohydrates and fats, are alone considered.^ Vitamin B2 • Aids in formation of red blood cells and antibodies • Essential for carbohydrate, protein and fat metabolism • Promotes general health • Necessary for the maintenance of...
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 ^ Can Calories: 0 Fat: 0g Cholesterol: 0mg Sodium: 45mg Total Carbohydrates: 0g Fiber: 0g Sugars: 0g Protein: 0g Vitamin C: 0% .
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 ^ Calories: 0 Fat: 0g Cholesterol: 0mg Sodium: 25mg Total Carbohydrates: 0g Fiber: 0g Sugars: 0g Protein: 0g Vitamin C: 0% .
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 They are treated under the following heads: I. The Chemistry of Digestion; II. The Mode of Formation of the Digestive Secretions; III. The Mechanism by which the Food is passed along the Alimentary Canal; IV. The Absorption of Food; V. Metabolism; VI. Excretion.
.I. Chemistry Of Digestion The essential step which prepares the ordinary food for utilization in the body, for the change into living matter, is digestion, a process which the food undergoes under the influence of the ferments or enzymes present in the gastro-intestinal tract.^ I found it to be interesting because it says that it doesn't matter what kind of diet change one under goes, low carb, high carb, high protein, hig...
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 .By this process it is broken down into simpler substances, which can be utilized by the body tissues for conversion into protoplasm and as the supply of energy.^ As a result, it can take more than twice as long for caseins to be broken-down into their amino acid subcomponents than whey and other proteins.
  • Bulk Nutrition - Optimum Nutrition 100% Casein Protein at discount prices! 8 January 2010 5:19 UTC www.bulknutrition.com [Source type: Academic]

 ^ Glucosamine and Chondroitin are substances that are produced in our bodies naturally and help serve as building blocks for your connective tissues.
  • Nutrition - Find great deals, lowest prices, and buy Nutrition at Shopping.com 8 January 2010 5:19 UTC www.shopping.com [Source type: General]

 ^ When you suddenly cut down calories to that low an amount your body thinks it is starving and goes into surviv...
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 .That part which is unsuited for use in the body is either passed as faeces or absorbed and excreted in the urine.^ If you don't correct under-nutrition, either your brain or some other part of your body is going to give.
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]
r. Enzyme Action generally. - The substances which bring about this change are known as ferments, enzymes or zymins. Formerly it was believed that there were two distinct classes FIG. 3. - Myristica fragrans. I. Male flower X 2.2. Female flowerX 2.
After Berg and Schmidt. From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer.
FIG. 2. - Myristica fragrans, seed cut through longitudinally. (Official.) g, Aril.
h, Outer integument, interrupted at r by the raphe.
m, Ruminated sperm.
n, Embryo (nat. size).
endo of enzymes, those which were living or associated with living cells, and those which were non-living. In 1897, however, E. Buchner and M. Hahn showed that from living cells (yeast) a ferment could be obtained which acted quite as well extracellularly as when it was bound up within the cell. .Subsequent work has shown that other organisms act by the enzymes they contain, so that it is now recognized that there is no essential difference between the living or organized ferment and the non-living or unorganized ferment.^ In an idealized setting, there is very little or no exchange of sediment between the pocket beach and the adjacent shorelines.
  • Beach Nourishment - Coastal Geology 20 November 2009 10:16 UTC www.csc.noaa.gov [Source type: Academic]

 ^ When doctors told me there was no more they could do, I found this site and found people who were going through the same symptoms I was going through thanks to Paxil.
  • All About Nutritional Supplements: Consumers Review Supplements, Vitamins, Herbs and Prescription Drugs 8 January 2010 5:19 UTC www.nutritionalsupplements.com [Source type: General]

 ^ In its idealized form, this type of beach is one where there is no sand present other than that resulting from beach nourishment.
  • Beach Nourishment - Coastal Geology 20 November 2009 10:16 UTC www.csc.noaa.gov [Source type: Academic]

 All ferments probably act as catalysators or catalysts. Catalysis is the process by which reactions are either initiated or accelerated by the mere presence of certain substances which remain unchanged during the process; to these substances the name of catalysators has been given. As an example of such catalytic action the acceleration of the decomposition of hydrogen peroxide (H 2 0 2) into water (H 2 0) and oxygen (0) by the action of a colloidal solution of platinum may be given. C. Oppenheimer defines an enzyme as a substance produced by living cells, which acts by catalysis. E. Fischer has shown that the action of ferments is specific, that is, the ferment only exerts its action on definite substances or substrates of definite structural arrangement. He has compared the relation of ferment to substrate to that of a key to its lock. .Ferments which bring about the breakdown of proteins are without influence on fats and carbohydrates; those which decompose fats leave proteins and carbohydrates untouched, and so on.^ A nutritionally sound approach to a high protein diet assists in building lean muscle without piling on fat and risking your health.
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 ^ Vitamin B2 • Aids in formation of red blood cells and antibodies • Essential for carbohydrate, protein and fat metabolism • Promotes general health • Necessary for the maintenance of...
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 ^ Can Calories: 0 Fat: 0g Cholesterol: 0mg Sodium: 45mg Total Carbohydrates: 0g Fiber: 0g Sugars: 0g Protein: 0g Vitamin C: 0% .
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]
The chemical composition of enzymes is unknown. .It has been assumed that they are protein in nature, but this is mainly because it has been found that when they are extracted from tissues they are apparently in combination with proteins.^ I found it to be interesting because it says that it doesn't matter what kind of diet change one under goes, low carb, high carb, high protein, hig...
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 In all probability the protein is there as an impurity owing to incomplete separation.
As regards the general properties of enzymes, most of them can be precipitated from their solutions by means of alcohol. They can also be carried down by fine precipitates of certain inorganic salts or by protein precipitation, e.g. when a precipitate of casein is produced by acidifying a casein solution with acetic acid. Most of the ferments are soluble in water or saline solutions, and in glycerin and water. The ferments are found to have an optimum temperature of action. This temperature in most cases ranges from 37° to 40° C. All true ferments are thermolabile, being destroyed at about 70° C. Ferments are hindered in their action to some extent by the general protoplasmic poisons, such as salicylic acid, chloroform, &c. The action of many of them is retarded when the products of their action are allowed to accumulate. .Just as when a chemical reaction is set up its rate tends to decrease and finally comes to a standstill before the reaction is completed - an equilibrium being established - so the reactions set up by enzymes also tend to come to an equilibrium before the complete conversion of the original substance.^ Thus, it is important for the stakeholder to understand that over several years the nourished beach width will decrease with the rate of this evolution decreasing and approaching a more or less equilibrium dry beach width.
  • Beach Nourishment - Coastal Geology 20 November 2009 10:16 UTC www.csc.noaa.gov [Source type: Academic]

 ^ Marion Nestle Just when the melamine scandal seemed over, new chemicals and cover-ups emerge.
  • The Atlantic Food Channel: Nutrition 8 January 2010 5:19 UTC food.theatlantic.com [Source type: General]

 In the case of certain enzymes at least this equilibrium may be reached from either side; thus the enzyme maltase may either bring about the breakdown of the sugar maltose to dextrose or cause a synthesis of dextrose to maltose.
Material acted on.
Enzyme.
Where found.
Pepsin
Gastric juice
Trypsin
Pancreatic juice
I. Protein .
Erepsin
Small intestine
Various autolytic
enzymes
Tissues generally
II. Fats. .
I Lipase
Pancreatic juice and
certain tissues
Ptyalin
Saliva
(salivary diastase)
Pancreatic diastase
Pancreatic juice
Maltase
Pancreatic juice
III. Carbohydrates
Small intestine
Invertase.
Small intestine
Lactase
Small intestine
Various tissue
diastases
Liver, muscle, &c.
A number of the body ferments have now been shown to exist in the tissues in an inactive form. This condition is known as the proferment or zymogen state, and before any action can be exerted it must be activated, usually by some specific substance, as in the case of the activation of trypsinogen by means of enterokinase. The following table gives a list of the principal ferments concerned in the digestion and metabolism of food-stuffs: - Certain oxydases, catalases and de-amidizing enzymes are found in the tissues generally and play an important part in the various metabolic processes.
2. Digestion in the Mouth. - The first of the digestive secretions which food comes into contact with is the saliva. This is the mixed secretion from the various glands, salivary and other, the ducts of which open in the mouth. The saliva, which is for the most part produced by the three large salivary glands, the parotid, the sub-maxillary and the sub-lingual, is a colourless or a slightly turbid viscous fluid with a faintly alkaline reaction and of low specific gravity. It contains a very small proportion of solids, which vary somewhat in amount and character in the secretions of the different glands. Mucin and traces of other proteins are present. Small amounts of potassium sulphocyanide may nearly always be detected. The functions of the saliva are twofold. First, it has a mechanical action moistening the mouth and the food and thus aiding mastication and swallowing by securing the formation of a proper bolus of food; it also assists by binding the particles together, an action of special importance when the food is dry. Second, in man and in some of the lower animals the enzyme ptyalin exerts an action in digestion on part of the carbohydrates of the diet. The starches or polysaccharides are broken down, first of all to the simple dextrins and then to the still more simple disaccharide, maltose. The further breakdown of the maltose is carried out in the intestine by the action of a ferment maltase which does not exist at all or only in the merest traces in the buccal secretion. The action of ptyalin on starches is thus very similar to that of acids, except that it stops at the formation of maltose. Ptyalin acts best at a temperature of about 40° C. and in a neutral or faintly alkaline medium, its action being inhibited by the presence of even very dilute solutions of the mineral acids. If the acid be in sufficient amount the enzyme is destroyed. For this reason the action ceases in the stomach whenever the bolus is completely permeated by the gastric juice. As it takes time for the gastric juice thoroughly to permeate the food mass, which remains for a considerable period in the fundus of the stomach unmixed with the secretion, salivary digestion goes on for about half an hour after food is taken.
3. Gastric Digestion. - The passage of food from the mouth to the stomach will be dealt with later. .The stomach has two digestive functions: (1) It acts as a store chamber permitting a full meal to be taken; (2) It acts as a digestive organ of importance in preparing the food for further attack in the intestinal canal.^ Alison E. Field Americans are replacing home-cooked meals with prepared foods--does that lead to obesity?
  • The Atlantic Food Channel: Nutrition 8 January 2010 5:19 UTC food.theatlantic.com [Source type: General]

 But the stomach cannot be regarded as an essential organ, since it has been removed in dogs and in man without apparent interference with nutrition and health.
Gastric digestion is brought about by the action of the gastric juice, a clear watery, colourless and strongly acid fluid with a specific gravity of about 1003. The amount of solids present is extremely small, about o 3%. They consist of protein, nucleic acid, lecithin and inorganic salts, in addition to the more important constituents, the enzymes and hydrochloric acid.
The amount of hydrochloric acid present in the juice varies with the period of digestion. In man the maximum acid concentration is about o. 2%. The acid exists in the stomach in two forms as free hydrochloric acid and as combined hydrochloric acid. The amount of each depends on various factors: (1) the secretion itself; (2) the nature of the food; and (3) the rapidity with which the stomach empties itself, &c. For instance, after a protein-free meal the hydrochloric acid is for the most part free, whereas, when protein is present, it combines with it and, unless secreted in very large amount, most of the acid is in a fixed condition.
The hydrochloric acid is formed by the activities of certain gland cells in the middle region of the stomach, and the fact that it does not exist as such in the blood proves that it is formed within these cells. .Further, it has been found that the gastric mucous membranes of starving dogs contain o 74% of sodium and potassium chloride, much more than is present in any other organ or in the blood plasma.^ In its idealized form, this type of beach is one where there is no sand present other than that resulting from beach nourishment.
  • Beach Nourishment - Coastal Geology 20 November 2009 10:16 UTC www.csc.noaa.gov [Source type: Academic]

 That the chlorine comes from the sodium chloride in the food has been shown by the fact that, when the tissues are deprived of this salt, and sodium bromide is given, hydrobromic acid may appear in the gastric secretion.
The hydrochloric acid is essential for the action of the gastric enzyme, pepsin, in splitting up the protein of the food. In addition to this, the acid has a slight action in splitting polysaccharides and disaccharides. Lastly, it. acts as a bactericidal agent, preventing bacterial decomposition from taking place, and it may thus prevent certain noxious bacteria, taken in in the food, from gaining access to the intestinal tract, where there is a chance of their flourishing in the rich alkaline medium. It is owing to the presence of hydrochloric acid that gastric juice can be kept for prolonged periods without undergoing putrefaction.
The quantity of juice secreted varies with the nature of the food consumed. Thus in one experiment, after the use of a test meal consisting of 25 grammes bread and 250 c.c. tea, there was a flow of 106 c.c., whereas in another case with an ordinary meal there was an output of practically 600 c.c. gastric juice.
Hour.
Quantities of Juice in c.c.
Digestive Power in mm.
Flesh.
Bread.
Milk.
Flesh.
Bread.
Milk.
1st
11.2
10 6
4.0
4'94
6.10
4.21
2nd
II.3
5'4
8.6
3.03
7.97
2' 35
3rd
7.6
4.0
9.2
3.01
7.51
2.35
4th
5'1
3.4
7'7
2.87
6'19
2.65
5th
2.8
3.3
4.0
3.20
5.29
4.63
6th
2.2
2.2
0.5
3'58
5.72
6.12
7th
1.2
2
..
2.25
5.48
..
8th
o 6
2.
..
3.87
5.50
9t
..
0.9
5'75
lot
..
0.4
..
Pawlow has shown that not only does the amount of juice secreted vary with the nature of the food ingested but that the digestive activity of the secretion also varies in the same way. He gives the following table: Quantities and Properties of Gastric Juice with Different Diets: 200 gms. Flesh, 200 gms. Bread, 600 c.c. Milk. Thus each separate food gives rise to a definite hourly secretion of the juice and to a characteristic alteration in its properties. The meat diet brings about a very rapid flow, the maximum output taking place within the first two hours; with bread the maximum output is even earlier. With milk somewhat later. When the juice is examined as regards its digestive activity, it is found that with meat the most active juice is secreted within the first hour, with bread in the second and third hours, and with milk in the sixth hour.
According to the nature of the food, the stomach seems to be stimulated to form a secretion which will best serve its purpose and give the minimum of waste. It thus works economically.
The principal ferment found in the gastric juice is pepsin, a ferment which acts only in the presence of a mineral acid. The action proceeds best at a temperature of about 37° C. in an acid medium of 0.2% to 0.3%. Pepsin is elaborated in the so-called chief cells of the gastric glands as an inert precursor-propepsin. It is only when it comes into contact with the acid of the juice that it is activated and rendered capable of attacking the protein of the food.
As already mentioned, the main function of the gastric juice is to deal with the protein moiety of the food and to prepare it for further digestion in the intestine.
.The first result of the action of this secretion on protein matter is to render it soluble-a metaprotein or acid albumin (syntonin), being formed.^ As a result, it can take more than twice as long for caseins to be broken-down into their amino acid subcomponents than whey and other proteins.
  • Bulk Nutrition - Optimum Nutrition 100% Casein Protein at discount prices! 8 January 2010 5:19 UTC www.bulknutrition.com [Source type: Academic]

 This body may be regarded mainly as the product of the action of the hydrochloric acid independently of the pepsin.
The following steps of decomposition are the result of the action of pepsin. From the metaprotein primary and secondary proteoses, the so-called proto-, heteroand deutero-albumoses are formed, and from these peptones are finally produced. .The result of this process of digestion or hydrolysis induced by the pepsin is that complex protein substances of high molecular weight are converted into simpler bodies of comparatively low molecular weight.^ I found it to be interesting because it says that it doesn't matter what kind of diet change one under goes, low carb, high carb, high protein, hig...
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 ^ When you suddenly cut down calories to that low an amount your body thinks it is starving and goes into surviv...
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 ^ High Protein Diet for Weight Gain .
  • Diet & Nutrition | LIVESTRONG.COM 8 January 2010 5:19 UTC www.livestrong.com [Source type: General]

 Formerly it was believed that the action of the pepsin on protein could not carry the decomposition further than the peptones, but recently it has been shown that still further splitting can be brought about, and that the simple amino acids of which the protein molecule is built up can be produced. This latter process, however, takes a very long time even under favourable circumstances, and it probably never occurs under normal conditions. The contents of the stomach-products of protein digestion-are passed on into the duodenum, chiefly as proteoses and peptones.
In addition to the principal ferment of the gastric juice some workers hold that another enzyme is present. This is the ferment rennet, rennin, or chymosin, the sole action of which, so far as is known at present, is to bring about the curdling of milk, the curd formed being dealt with in the ordinary way by the pepsin. Clotting of milk under the action of rennin occurs at a suitable temperature with great rapidity. This process is said to take place in two stages: (I) the rennin converts the caseinogen of the milk into paracasein, and (2) this paracasein unites with the lime salts present in the milk and forms the curd or precipitate. That lime salts are absolutely essential for this process of clotting has been shown by the fact that, if they are removed by precipitation as by oxalates, no clotting will take place even after the addition of a large amount of active rennin. Immediate clotting takes place, however, when the necessary lime salts are restored. Many observers now hold that this rennet action is not the property of a specific ferment but simply another phase of the action of pepsin. For this view, which has been put forward by wellknown workers, there is much to be said and certainly the power of curdling milk is not confined to the stomach, but has been found in various tissue extracts, and, indeed, wherever proteolytic enzymes are found.
The speed with which the stomach is emptied depends to a great extent on the nature of the food. Plain water leaves the stomach almost at once, salt and sugar solutions at a somewhat slower rate. Milk under the action of rennin curdles. The whey rapidly leaves the stomach, whereas the casein and fat are retained for further treatment. On a mixed diet, emptying of the stomach in man proceeds very slowly, requiring about four hours. Cannon, by feeding with food impregnated with bismuth and using X-rays, showed that carbohydrates leave most rapidly, then mixtures of carbohydrates and proteins, then proteins, then fats, and finally mixtures of fats and proteins. The diet which remains longest in the stomach is a mixture of fats and proteins-rich food, as it is popularly called. Here two factors enter to prevent rapid emptying: (I) the presence of much fat, and (2) the acid secretion engendered by the abundant protein.
There is no doubt that fats present in fine emulsion can be decomposed in the stomach. The action proceeds in a medium which is slightly acid or neutral, being entirely prevented by the presence of strong acids and alkalis. Many workers believe this gastrolipase to be of pancreatic or intestinal origin, and suppose that it gains entrance to the stomach by a reflux 'flow through the pylorus. Evidence is accumulating to show that this view is correct.
By means of pepsin and gastrolipase proteins and fats are dealt with. No specific enzyme for carbohydrates has been found in the stomach in man. Certainly a small amount of polysaccharide decomposition takes place, but this is dependent (I) on the ptyalin which comes from the mouth, and (2) on a certain amount of hydrolysis due to the action of the free hydrochloric acid.
4. Digestion in the Intestine.-The passage of food from the stomach to the intestine will be considered later. The food so far digested in the stomach is known as chyme, and it is passed on to undergo intestinal digestion under the influence of (I) the enzymes of the pancreas, and (2) of other enzymes present in the different secretions of the intestine. Digestion in the intestine may accordingly be described under these two heads.
(a) Pancreatic Digestion.-The pancreatic juice is the secretion from the pancreas and is discharged into the duodenum. The secretion obtained from a fistula of the pancreatic duct varies in character according to whether the opening into the duct has been made recently or some time before the examination. It is a clear, usually thin fluid with a specific gravity of about 1008, and with an alkaline reaction. It contains a certain amount of protein and ash. The most important inorganic constituent is sodium carbonate, which gives the alkaline reaction (alkalinity is, as NaOH = o 47%. This alkaline salt, along with that contained in the intestinal juice, plays an important part in neutralizing the acid chyme.
In the pancreatic secretion there are at least three important enzymes, each with a definite action: (a) trypsin, the proteolytic enzyme which brings about the further breakddwn of the food proteins; (b) a diastase which deals with the carbohydrates, and (c) a lipase which acts on the fats.
(a) Trypsin.-This ferment, in the form in which it is secretedtrypsinogen-is inert. Before it can exert its hydrolytic action it must be activated. This activation is brought about by another enzyme which is found in the intestinal tract-enterokinase. The conversion is brought about as soon as the trypsinogen comes into contact with the enterokinase, the merest trace of which suffices to activate a large amount of trypsinogen.
Trypsin acts on the protein j ust as pepsin does, by bringing about hydrolytic changes. It differs from the latter in acting best in an alkaline or neutral medium. Its effect is much more energetic than that of pepsin, so that the protein molecule is more completely decomposed. Whilst it generally finishes the decomposition which the pepsin has begun, it can break down the original protein quite as easily if not more easily than does pepsin, and it carries the splitting as far as the comparatively simple crystalline bodies, the amino acids, or groups of these, the polypeptides, bodies intermediate between the complex peptones and the simple amino acids of which the protein is built up.
The character and properties of the products formed in such digestion depend on the nature of the protein acted upon. As will be seen from the following table these proteins vary fairly widely in the proportion of amino acids which they contain.
Caseinogen.
Gelatine.
Globine
from Oxy-
haemoglobine.
Elastine.
Glycocoll
. .
16 5
. .
25.75
Alanine. .
0 9
o 8
4 19
6.58
Leucine. .
10.5
2 I
29.04
21.38
aProline. .
3 I
5.2
2.34
I'74
Phenyalanine
3.2
0.4
4'24
3'89
Glutamic acid
10.7
o 88
1.73
o 76
Aspartic acid
I .2
0.56
4.43
Cystine
o 06
. .
0.31
..
Serine. .
0.2
..
0.56
Oxyproline .
0.25
3 o
1.04
..
Tyrosine .
4'
I' 33
0.34
Lysine. .
5.80
2.75
4'28
Histidine .
2'59
0.40
Io 96
..
Arginine. .
4'84
7 62
5'42
0'3
Tryptophane
1-
..
Present
ioo Grammes Protein yielded Whether any of the polypeptides found in digestion are further broken down in the course of normal pancreatic digestion is a moot point, but E. Fischer and E. Abderhalden have shown that many of the synthetic polypeptides prepared by them can be broken into their constituents by the action of trypsin. The previous peptic digestion seems to play some part in the extent to which tryptic digestion is carried out, as one of these observers has demonstrated that protein digested first with pepsin and then with trypsin gives a smaller yield of polypeptide and a larger yield of monamino acids than when digestion has been carried out with trypsin alone.
Table of contents
1 b. Diastase
2 c. Lipase
3 b. Intestinal Digestion
4 5. Bile
5 Faeces
6 2. Gastric Glands
7 3. Pancreatic Secretion
8 4. Intestinal Juice
9 Deglutition
10 Stomach Movements
11 Intestinal Movements
12 Defaecation
13 Vomiting
14 Intestine
15 Carbohydrates
16 Protein
17 Proteins
18 Fats
19 2. Muscular Work
20 3. Internal Secretions
21 Pancreas
22 Creatinin

b. Diastase

This ferment is found in the pancreatic juice apparently secreted in an active form, although some observers hold that it also is secreted in a zymogen form. It is practically identical in its action with the ptyalin of the saliva, converting starch into maltose. It deals with all the starchy food which has escaped conversion into the simple sugars by the ptyalin.

c. Lipase

Most of this ferment, if not all, is apparently secreted in the form of a zymogen. There is evidence that the bile is the activating agent here, just as the enterokinase acts in the case of trypsin. Lipase can act in any medium acid, neutral, and alkaline, and both on emulsified and non-emulsified fats. It converts the fats by a process of hydrolysis into fatty acids and glycerin. Kastle and Loevenhart found that not only can this enzyme break up fats into their components, but that it also has the power to act in the reverse direction, and in this way bring about the union of fatty acids and glycerin so as to form fats, a process which occurs in the intestinal epithelial cells after absorption.
In addition to these three enzymes the pancreatic juice may contain traces of others, for example, a rennet-like ferment which curdles milk. This again, as in the case of the stomach rennet, is held by some to be only another phase of proteolytic action. Maltase is also said to be present in small amount, as is also lactase under certain conditions. In pancreatic, as in gastric digestion, the nature of the food is said to play a part in controlling the amount and the composition of the secretion with respect to its ferments. The action, if it does exist, is not very well defined.

b. Intestinal Digestion

By this is meant the other digestive processes which go on in the intestine under the action of the secretion of Lieberkiihn's follicles - the succus entericus. This is a yellowish, often opalescent, strongly alkaline fluid. The alkalinity is due to the presence of sodium carbonate. It contains a small amount of protein, shed epithelial cells, &c. The secretion of some 170 c.c. in 24 hours has been observed in a short loop of human intestine by H. S. Hamburger and E. Hekma, but it is almost impossible to get a measure of the actual amount of secretion from the whole gut. Most of the ferments are present in very small amount in the intestinal juice. They seem to be actually within the epithelial lining of the intestine, for extracts made from the intestinal mucous membrane are richer in ferments than the secretion.
Apparently the intestinal secretion contains no trace of a ferment acting on native protein, but a ferment - erepsin - is present in fair amount in the intestinal mucous membrane and in small amount in the secretion, which acts in an alkaline medium on proteoses, peptones, and on casein, converting them into crystalline products of the nature of amino acids.
Another ferment, arginase, has been isolated from the intestinal mucous membrane by A. Kossel and H. D. Dakin, which splits the diamino acid arginin into urea and ornithin. A lipase has also been detected which is very similar to pancreatic lipase; it, however, attacks only emulsified fats.
Several carbohydrate hydrolysing enzymes have been described in the small intestine. Invertin, the ferment which splits cane-sugar, is present in small amount in the secretion, more abundantly in the extract of mucous membrane. In all probability it deals with the saccharose after or in process of absorption. Maltase is also present in large amount, and here again in greater amount in the extract than in the secretion. The presence of lactase has been much discussed, and it seems probable that suckling animals do possess this enzyme. Some workers have stated that an intestinal diastase is to be found, but, if so, it is present in very small amount.
In the large intestine a small amount of erepsin has been discovered at the upper end. Any digestion which does take place is probably either bacterial in origin, or due to ferments which have originated in the lower end of the small intestine, and which have been carried down.

5. Bile

This fluid, in all probability, has little direct action in ordinary digestion, although it contains substances which act indirectly. The bile salts act as solvents for fats and fatty acids, and as activators of pancreatic lipase. The salts also serve to keep cholestrin in solution. Bile is to be looked upon rather as the excretion, the result of the hepatic metabolism, than as a digestive juice. Various workers have shown that when the bile is prevented from entering the intestine owing to a fistula having been made, the animal or patient may continue to enjoy good health, thus proving that this fluid is not essential to any of the digestive processes which normally take place.
Bile as secreted has an orange-brown colour, but the colour varies according to the pigment present. It is more or less viscous (not so viscous as bile taken from the gall bladder) and has a specific gravity of about Iwo. It has a slightly alkaline reaction, a bitter taste and a characteristic smell. The daily output is, for a normal individual, over 500 c.c. On analysis it is found to have over 2% of solids, of which more than half are organic. It contains in addition to a nucleo-albumin, derived mainly from the bile passages and gall bladder, bile acids, bile pigments, cholesterin, lecithin, fats, &c. The most abundant solids are the salts of the bile acids, of which in man the most important is sodium glycocholate, sodium taurocholate being present in very small amount. The bile acids are formed in the liver cells, and when the duct is ligatured they tend to accumulate in the blood.
The pigments amount to only about 0.2%. In human bile the chief pigment is bilirubin, whilst in herbivora biliverdin is more abundant. They are derived from the haemoglobin of the blood, but the pigments are iron-free. They may be regarded as purely excretory products arising from the breakdown of the haemoglobin of effete blood corpuscles.
Cholesterin is a monatomic alcohol, and is probably a waste product. It occurs in the bile only in small amount, and there is some evidence that it is not secreted by the liver cells but is added to the bile from the bile passages. Fats and lecithin are both derived from the liver cells. Of the inorganic constituents phosphate of calcium is the most abundant.
The secretion of bile is practically continuous, but it seems to enter the duodenum intermittently. The taking of food increases the flow of bile, the amount of the increase depending to a certain extent on the nature of the food. A protein meal has been found to have the greatest effect and a carbohydrate one the least. The entry of the acid chyme into the duodenum is the stimulus which brings about the ejection of the bile. Pressure on the liver also seems to cause a flow (see section II.).
In connexion with bile secretion attention may be drawn here to a peculiar enterohepatic circulation which is stated to exist. The bile salts are partly absorbed from the intestine, to be carried again by the portal blood to the liver and to be again eliminated. By this circulation the entrance of various alkaloidal and ptomaine poisons into the general circulation may be prevented.

Faeces

The bulk of the waste matter arising from the foods along with the secretions from the alimentary canal form the faeces. On an absorbable diet the faeces are almost purely intestinal in origin. As a channel of excretion of nitrogenous metabolic waste products they are not very important, although the work of C. Voit indicates that they do play a certain part. The nature of the excreted nitrogenous substances has not been fully examined. Of the inorganic constituents iron is probably for the most part excreted into the large intestine. It is, however, very difficult to come to any definite conclusion as to what is unabsorbed material and what excreted.
II. THE Mode Of Formation Of The Digestive Secretions 1. Salivary Glands. - The secretion from the various glands is generally evoked by nervous impulses, through the secretory nerves. K. Ludwig found that the stimulation of the chorda tympani produced a copious flow of watery saliva from the submaxillary gland, and a general dilatation of the blood-vessels supplying the gland. The same is the case in the sublingual gland. In addition to the chorda tympani fibres also pass to the gland through the cervical sympathetic, and when these are stimulated the saliva excreted is viscous and turbid, and contains much solid matter, while the blood-vessels are contracted. The conclusion formerly drawn was that the flow of saliva was dependent on the increased blood supply. But it has been definitely proved that true secretory fibres exist. If atropine be administered before stimulation of the chorda tympani, the dilatation of the vessels takes place, but no flow of saliva. Further, if the circulation be cut off from the gland the stimulation of the chorda tympani may cause a temporary flow of saliva.
The parotid gland is supplied by the auriculo-temporal nerve which receives its secreting fibres from the glossopharyngeal. Stimulation of these fibres brings about an abundant watery secretion poor in solids. Stimulation of the sympathetic fibres system is not followed by any salivary flow, yet it has an effect on the gland, for, if after the sympathetic has been stimulated a secretion be evoked by stimulation of the glossopharyngeal nerve, the saliva secreted is very rich in organic solids.

2. Gastric Glands

The control of the gastric secretion seems to be under two entirely different mechanisms. Pawlow has clearl y shown that the stomach is supplied with secretory nerves which reach that organ through the vagus. The stimuli which bring these nerves into action are the sight, the odour or the taste of food. That the course of the stimulus is through the vagus is shown by the fact that an abundant flow of juice may be caused so long as the vagi are intact, but this flow does not take place when these nerves are cut. Between the stimulation and the secretion there is a lengthy latent time amounting to several minutes. The other stimulus of the secretion is apparently a chemical one. Pawlow states that mechanical stimulation of the mucous membrane fails to bring about a flow of juice, but Beaumont in his classical observation on the stomach of St Martin found that the insertion of a tube did cause a flow. There may be certain substances either present in the food or developed in the course of digestion, which directly stimulate the secretion originally started by a nervous reflex. E. Starling has drawn attention to this chemical mode of stimulating different organs. To the substances known and unknown which evoke the action, he gives the name of hormones, and such "hormone" action he does not limit merely to the secretory organs but extends to all cases where one organ is stimulated by chemical products formed in the same or another organ. Attention has already been drawn to the influence of different food-stuffs on the amount and nature of the gastric secretion.

3. Pancreatic Secretion

The stimuli which evoke this secretion are again two in number. Many have failed to demonstrate that the secretion of the pancreas is under nervous control, but Pawlow and his school have shown that stimulation of the vagus evokes a secretion of pancreatic juice. This flow, as in the case of the stomach, has a latent period of several minutes. Most modern workers hold that the most effective stimulus to the pancreatic flow is the chemical one - a hormone discovered by W. Bayliss and E. Starling, who found that extracts of the duodenal mucous membrane made with dilute hydrochloric acid when injected into the blood caused a flow of pancreatic juice. The active substance present in this extract is known as "secretin," and is supposed to be formed under natural conditions by the action of the acid chyme on a prosecretin. This secretin is not of the ordinary zymin nature, as it is not destroyed by boiling and is soluble in alcohol. The secretin when formed must be absorbed into the blood and then carried round the circulation to the pancreas before it can act.

4. Intestinal Juice

The mode of action of the stimuli which evoke this secretion has not yet been fully investigated. As has been stated, it is quite possible that very little ferment is secreted, and that ferment action mainly takes place within the cells after the various substances have been absorbed.
How far the flow is controlled by nervous action, and how far by hormone action, is not known.
Motor Mechanism Of The Alimentary Canal Mastication. - This is a purely voluntary act, and consists of a great variety of movements produced by the various muscles in connexion with the lower jaw. By the act of chewing the food is thoroughly broken up and intimately mixed with the saliva.

Deglutition

The food after thorough mastication is collected on the surface of the tongue, principally by the action (voluntary) of the buccinator muscles, and by the contraction of the tongue muscles it is passed backwards. As soon as the food by the action of the tongue enters the pillars of the fauces the action becomes involuntary and reflex. The soft palate is raised to prevent the food entering the nasal cavity, and the larynx is shut off by closure of the glottis, and approximation of the arytenoid cartilages to one another and to the back of the epiglottis. The food is now passed on into the oesophagus proper by the constrictors of the pharynx. In the oesophagus the downward movement varies with the nature of the food swallowed. If it be fluid it reaches the lower end of the oesophagus in about three seconds and lies at the lower end of the gullet for two or three seconds before entering the stomach. When the consistency is firmer the progress downwards is much slower. Either by the force exerted by the wave of contraction passing down the gullet or by some inhibition of the sphincter, the cardiac orifice opens and permits the food to enter the stomach.

Stomach Movements

For our knowledge of these we are indebted principally to the work of Cannon, who studied them by feeding an animal with food containing bismuth and then following the movements of the shadow of the food on a screen by means of the X-rays. Soon after food is taken it is found that a contraction begins somewhere about the middle of the stomach and slowly passes towards the pylorus. This is followed by others, in man at regular intervals of about twenty seconds, so that the pyloric part of the organ is soon in active peristalsis. The fundus of the stomach is not actively concerned in these movements; it simply acts as a reservoir. At certain periods, but not with each peristaltic wave, the pyloric sphincter relaxes and allows a portion of the fluid acid chyme to escape into the duodenum. It only opens when stimulated by fluid material; if solid food be forced against it it remains tightly closed. Griitzner, by experiments with feeding with different coloured foods, has shown that the food at the fundus may remain undisturbed for quite prolonged periods. In this connexion it must be remembered, of course, that the food is not lying loose in a sack larger than the contents. The cavity of the stomach is only the size of the amount of food present; in other words, the food exactly fills the cavity. The motor nerve fibres to the stomach run in the vagi, which also contain fibres inhibitory to the cardiac sphincter. The splanchnic nerves mainly contain inhibitory fibres. The automatic movements are probably in connexion with the intrinsic plexus of Auerbach, since they continue after section of the extrinsic nerves.

Intestinal Movements

The intestines owe their peculiar movements to the arrangement of their muscular coats, which are disposed in two layers, an inner circular, and an outer longitudinal. The movements are of two kinds, the so-called swaying myogenic contraction and the peristaltic waves. The former are rapid and have very little to do with the downward movement of the contents. Probably their action is to mix the contents, since Cannon has shown that these contents, in the lower animals at least, get divided into segments. From time to time the separated segments are caught in the course of a peristaltic wave and carried downward a short distance. Then again in their new situation the rhythmic contractions break up the contents anew.
The peristaltic movements are much more powerful. Under normal conditions they begin at the pylorus and passing downwards carry the intestinal contents onwards. The normal movement progresses slowly, although under abnormal conditions peristaltic waves may become extremely violent and rapid, and may indeed run over the whole length of the intestine within a minute. The muscular coat in front of the contracting zone is relaxed, as is that behind the wave. The waves are probably due mainly to the circular fibres, the longitudinal pulling the gut up over the contents as they are forced onwards. The downward movement seems to be due to some definite arrangement within the intestinal wall, since it has been shown that, when a segment of bowel has been cut out and then the continuity of the canal made good by fixing the section so that the lower end of the excised portion is fixed to the upper divided end of the real gut, upward peristalsis takes place in this segment. An anti-peristalsis has been described in which the movements are all towards the stomach. Under certain conditions the introduction of foreign substances, as hairs, &c., may evoke such anti-peristaltic waves.
The rhythmical movements are held by some to be purely myogenic in origin, as they still continue after section of all the nerves and when the intrinsic ganglia in the intestinal wall have been thrown out of action by the application of nicotine. But recent work by R. Magnus would tend to show that they are controlled by Auerbach's plexus. Peristaltic waves, on the other hand, according to W. Bayliss and E. Starling, although they continue and indeed may become more energetic after section of the extrinsic nerves, are prevented by the application of nicotine and cocaine; in other words, it is presumed that peristalsis is a complicated reflex action through the intrinsic ganglia. The intestines are therefore not dependent for their movement on their connexion with the central nervous system, although of course their activity is more or less regulated by such a connexion.
As regards the movements of the large intestine, they resemble those of the small, although they are much less frequent. The forward movement is slow, thus permitting of the solidification of the contents by the removal of the water. In the first part of the large intestine anti-peristaltic movements are frequent, the regular peristaltic downward movements only becoming prominent when the descending colon is reached to carry contents to the rectum. The anti-peristalsis serves a useful purpose in giving time for the absorption of the fluid in the formation of faeces. The rate at which the contents travel along the intestine varies greatly. Under average conditions the food residue reaches the ileo-caecal valve between the small and large intestine at about four to four and a half hours after a meal, while it takes nine hours to reach the splenic flexure of the colon.

Defaecation

Food residues, cellular debris and substances derived from the various secretions of the gastro-intestinal tract are forced downwards by peristalsis, and eventually reach the rectum and accumulate there as the faeces. The pressure of the solid and semisolid mass gives rise to a definite sensation and a desire to empty the rectum. The faeces are retained within the canal partly by the horizontal direction of the rectum before it opens into the anal canal, and partly by the action of two sphincter muscles. At the act of defaecation the strong internal sphincter is first of all relaxed, but unless the rectal stimulus is very strong, the external can be kept contracted, as it is to a certain extent, under the control of the will. The act of defaecation normally is partly voluntary and partly involuntary. The voluntary part consists in the contraction of the abdominal muscles, the closure of the glottis, and the relaxation of the external sphincter and of the levator ani muscle, thus allowing the horizontal part of the rectum to become more vertical; the involuntary in the energetic contractions of the muscular walls of the colon and rectum which sweep the contents of the whole colon downwards. There is a centre in the lumbar enlargement of the spinal cord which presides over the sphincter muscles and probably over the whole involuntary mechanism of defaecation.

Vomiting

Sometimes the gastric contents are ejected through the cardiac opening of the stomach instead of through the pylorus. The act is a reflex one, probably originally protective in nature, irritation of the gastric mucous membrane being the most frequent cause. The act is generally preceded by a feeling of nausea and a copious salivation, succeeded by a series of powerful expiratory efforts with the glottis closed. The diaphragm is held firmly contracted, then a convulsive contraction of the abdominal muscles with a simultaneous opening of the cardiac orifice of the stomach brings about the sudden ejection of the contents. The wall of the stomach may also contract and press upon the contents. During the act the glottis is firmly closed, and at the same time, if the act be not too 925 violent, the gastric contents are prevented from entering the nasal cavity by the contraction of the soft palate.
IV. Absorption Mouth. - No absorption of food-stuffs takes place here Stomach. - Absorption from the stomach occurs only to a small extent. Water passes rapidly through the stomach and is practically unabsorbed. Salts are apparently absorbed in a limited amount from their watery solution, the extent of absorption depending to some extent on the concentration of the solution. Sugar is also absorbed to a small extent from its solutions, the greater the concentration the greater being the amount of sugar taken up. Alcohol is readily absorbed from the stomach. A small amount of the products of protein digestion may be absorbed. There is no evidence that fats are absorbed under any conditions in the stomach.

Intestine

The greatest absorption of the foods takes place in the intestine, especially in the small intestine. It has been shown that over 85% of the protein has disappeared before the lower end of the small intestine is reached. How does the absorption take place? There are two channels for the removal of the material from the intestine: (r) the blood capillaries spread in the villi, and (2) the lacteals also present in the viii. The foods may reach the blood direct or through the various lymph channels into the thoracic duct and finally into the blood. The lacteals of the villi are channels for the absorption of the fatty parts of the food. The products of the digestion of the proteins and carbohydrates reach the body directly through the capillaries via the portal system.
Can absorption be explained by the ordinary laws of diffusion and osmosis, or are there certain selective activities of the living epithelial lining ? The work of R. Heidenhain, E. Weymouth Reid, and others shows clearly that whatever part the physical laws play in this exchange, there are other activities also at work. For instance, an animal's own serum can be readily absorbed from its intestine, as can also salt and other solutions of higher concentration than that of the blood. Such absorption cannot be explained by ordinary physical laws. In all such cases of absorption the epithelial lining of the gut must be intact and uninjured. 0. Cohnheim and others have shown that when the epithelial lining is damaged or destroyed, the intestinal wall behaves like any other animal membrane, and the physical laws. governing osmotic pressure come into play. Whether the nervous. system plays any part in this absorption is not yet determined.
The form in which the various products resulting from digestion are absorbed must next be considered.

Carbohydrates

These reach the body, as already mentioned, by way of the blood, and in the form of monosaccharides or simple sugars. F. Rohmann found that the absorption of the disaccharides is dependent on the invert ferment action, and not upon their osmotic characters. E. Weinland too has shown that if lactose be put into a lactase-free intestine, no absorption takes place, the lactose gradually disappearing under bacterial action, whereas when the ferment lactase is present glucose and galactose the products of its splitting are absorbed as readily as cane-sugar and maltose. E. Voit has also demonstrated the fact that the body deals with its carbohydrate supply in the form of mono-saccharides. He injected solutions of various sugars, monoand di-saccharides, and found that the simple sugars were retained, whereas the double sugars were excreted in the urine. The only di-saccharide which can be dealt with in the body is maltose, as there is a maltase present in the blood which splits it. Carbohydrates which are not absorbed from the intestine are disposed of by bacterial action, giving rise to various fatty acids, carbon dioxide, &c.
Fats. -Fats are absorbed from the intestine in the form of fatty acids and glycerin; i.e. in the form in which they exist after the action of the lipase. That a resynthesis takes place in the epithelium is shown by the fact that fatty acids are of equal value with fat as a source of energy, and that as fat absorption goes on fat droplets are seen to grow in the protoplasm away from the free margin of the cells. As already mentioned, the fat is removed by the lacteals from the cells to the thoracic duct, and then to the general circulation. A small amount of the fat may pass into the body via the blood, but this is practically all retained by the liver. The amount of fat absorbed depends a good deal on the nature of the fat, especially with reference to its melting-point, fats of low melting-point being most readily taken up.

Protein

The older workers held that the protein was absorbed in the form of proteose and peptone. In support of this it was stated that both proteoses and peptones could be detected in the blood stream. The result of the most recent work tends to show that the material is absorbed in the form of the amino acids either simple or in complex groups, the polypeptides, and that if proteoses or peptones be absorbed they are attacked by the intra-cellular enzyme erepsin, which breaks them down into the simpler products as soon as they are within the intestinal mucous membrane. Certain proteins appear to be absorbed unchanged; for instance, blood serum disappears from the intestine without apparently any change through zymin attack. This fact is made use of in practical medicine, as, when administration of food by the mouth is impossible, patients are frequently kept alive by the giving of nutrient enemata. That the food thus given is absorbed is shown by the increase of nitrogen excretion in the urine.
In the large intestine very little absorption of nutrient matter takes place under normal conditions, mainly of course because most of the absorbable material is removed whilst the food is in the small intestine. That protein matter can be absorbed is shown by the above statement regarding nutrient enemata. The principal substance absorbed here is water; and thus the excreta become firm and formed.
V. Metabolism In all living matter there is a constant cycle of chemical changes going on, a constant breaking down (catabolism), and a correspondingly constant building up (anabolism). Unless the former is covered by the latter wasting and finally death must supervene. These two changes together make up the metabolism, and the study of this involves a study of the fate of the food absorbed both when it is used immediately and after it has been stored in the tissues of the body. Protein matter is undoubtedly the main constituent of protoplasm, but in what form it exists there is absolutely unknown. One thing is certain, that for the maintenance of life a constant supply of protein matter is necessary. In fact it might be said that this is the essential food and keeps the body alive, fats and carbohydrates being merely subsidiary. In the mammalian organism with which we are specially concerned a supply of these latter substances is also necessary to yield the energy required. The amounts of these various food stuffs which should be present in a suitable diet are dealt with under Dietetics. Here we are only concerned with the part played by the different materials in the various chemical changes which are the basis of vital activity.
Not many years ago physiologists were very much in the position of unskilled labourers who saw loads of heterogeneous material being "dumped" for building purposes, but who did not know for what particular purpose each individual substance was used. Thanks, however, to the brilliant work of E. Fischer we are no longer in this position. Gradually our knowledge is being broadened by actual facts obtained by direct experiment, or by inference from previous experiments. But it is still far from complete. It is only possible to outline what is at present known about the part played by the different food constituents in metabolism.

Proteins

Since these alone contain the nitrogen necessary for the building up and repair of the tissues they are essential and will be dealt with first. In considering the digestion of proteins it was shown that in all probability all protein food was reduced in the intestine to comparatively simple crystalline bodies. .O. Loewi has shown that an animal can be maintained in health without loss of weight by feeding it on a diet consisting of amino acids obtained by prolonged pancreatic digestion in place of proteins.^ Diet & Weight Loss .

 In addition to these acids abundant carbohydrates and fats were given. It has since been shown that the presence of carbohydrate a certain amount of is absolutely essential before utilization of the amino acids can take place. Further, it has been demonstrated that only a mere fraction of the total amino acids resulting from pancreatic digestion is sufficient as the source of nitrogen supply for the animal organism. Not only so, but, in spite of the attempt to insist on the polypeptides as being the valuable nuclei for the rebuilding up of protein in the body, it has been shown that mixtures of amino acids from which the polypeptides have been removed can serve as the nitrogen supply.
What then does the body gain by breaking down food material to such simple bodies, if it is immediately to be resynthesized ? This complete breakdown appears to be to facilitate rebuilding. The protein in the protoplasm of each animal is characteristic and to build up these different proteins the material must be separated into its nuclei. An experiment carried out by E. Abderhalden shows this very clearly. A protein gliadin absolutely different in constitution from the proteins of blood plasma was fed to an animal from which much of its blood had been removed, so that an active reformation had to take place. The question to be solved was whether by feeding with a protein so absolutely different in constitution the nature of the freshly forming serum protein could be radically changed. But the newly-formed serum was found to be exactly the same in constitution as the old. The tissues had selected simply those nuclei of the gliadin which were required and had rejected the others.
In addition to this breakdown of protein in the intestine, another factor of importance comes into play. After absorption from the lumen of the gut the amino acids are not wholly conveyed as such by the portal blood to the liver. That the portal blood contains a greater amount of ammonia than the systemic blood has long been known, and Jacoby and Lang have shown that many tissues, and among them the intestinal tissues, are able to split off from the amino acids their amino group NH 2. Thus it would seem probable that any excess of the amino acids formed does not reach the liver as such but denitrified as members of the fatty acid series. The ammonia split off is also conveyed to the liver and is excreted for the most part as urea, within the first few hours after a protein meal. Thus, in all probability very early after absorption and before the products of digestion enter into combination or any synthesis occurs, all excess of the absorbed nitrogen is disposed of. The rest of the products circulate in the blood, yielding to the cells the materials of which they are in need. On the other hand some investigators still hold that resynthesis into a neutral protein like serum albumin takes place in the intestinal wall immediately after absorption of the digest products. That the leucocytes play an important part in carrying the products of protein digestion to the tissues is indicated by the enormous increase in their number which occurs during the digestion and absorption of protein foods. How they act, whether simply as carriers of the products of protein digestion combined or uncombined, and how they give the material to the tissues is unknown.
Carbohydrates are generally assumed simply to serve the purpose of yielding energy in their combustion to CO 2 and H 2 O, and to act as protein sparers, i.e. they save the ingestion of large amounts of costly protein material as a source of energy. There may, however, be other activities in which the ingested sugars play a part, for instance, in the utilization of the nitrogen of proteins. It has already been indicated that the nitrogen in the products of pancreatic digestion can be used only when a sufficient amount of carbohydrates is given at the same time. Only carbohydrates seem to be able to do this, for it has been found that when isodynamic amounts of fat are given the utilization does not take place.
When taken into the body in excess of the immediate requirements the sugar is not utilized all at once, but any excess is stored in the form of glycogen both in the liver and the muscles. This glycogen is an insoluble polysaccharide, and is only utilized according to the requirements of the body, especially during muscular exertion. Carbohydrates, when taken in in excess, are also stored in the tissues in the form of fat. This was demonstrated by the feeding experiments of Lawes and Gilbert at Rothamstead. They took two young pigs of a litter, killed and analysed one, then fed the other for a definite time upon food of known composition, determining the amount of protein absorbed by analysing the urine and the faeces. They then killed the pig and by analysis ascertained the amount of fat put on. They found that this was far in excess of the amount of the protein of the food which had been absorbed and was also in excess of what could have been formed from the small amount of fat in the food. The fat must therefore have been formed from the carbohydrates of the food. The consumption of larger amounts of sugar than can be used or stored as glycogen results in its passing straight through the body and being excreted in the urine. This condition is known as alimentary glycosuria. The power of using and storing sugar varies greatly in different individuals and in the same individual at different times.

Fats

The fats simply serve as stores of energy. After ingestion, if in small amount, they are, like carbohydrates, oxidized to the same final products C02, and H 2 O. If in larger amount they are stored as fat, to serve as a reserve in case of need, in the body tissues. Like the carbohydrates they serve as the sources of part of the energy dissipated as heat, but they are not so efficient as sparers of protein material, evidently in part at least because they are less easily digested and absorbed.
Factors which influence Normal Metabolism. Fasting. - During fasting the body draws upon its own reserve of stored material for the requirements in the production of energy, and the rate of breakdown varies with the energy requirements. An individual who is kept warm in bed therefore stands fasting longer than one who is compelled to take exercise in a cold place. The breakdown of tissue during the early days of a fast is much greater than later, for as the fast progresses the body becomes more economical in its utilization of tissue. During a fast the tissues do not all waste at an equal rate; those which are not essential are utilized at a much greater rate than those which are essential to the maintenance of the organism. For instance, it has been shown that during a fast the skeletal muscles may lose over 40% of their weight, whereas an essential organ like the heart loses only some 3%.
The essential tissues obtain their nourishment from the less essential probably by ferment 'action, a process which has been termed autolysis. The autolytic products of the stored material in the tissues are practically identical with those which arise during the ordinary gastro-intestinal digestion.

2. Muscular Work

The muscular tissue plays the most important part in general metabolism. Not only is muscle the most abundant tissue present, but it is constantly active and is the great energyliberating machine of the body. Formerly it was believed on the authority of Liebig that muscular work was done at the expense of the protein material, but it has been conclusively shown that the real source of energy in moderate work is the non-protein material, carbohydrates and fats; of these the former plays the greater part in a man on ordinary diet. If, however, the supply of non-nitrogenous material be insufficient, then the energy has to be supplied by the protein and the output of nitrogen is thus increased. Variations in the amount of creatinin and uric acid (both products of muscle metabolism) excreted have been described. In hard work it is sometimes found that there may be no immediate rise in the nitrogen output on the day of the work, but that an increase is manifest on the second or third day after. While the excretion of nitrogen shows no increase proportionate to the work done, the output of carbon dioxide produced by the combustion of the carbohydrates and of the fats is increased proportionately to the work done.

3. Internal Secretions

Evidence is accumulating to show that the activities of the various tissues of the body are presided over and controlled not merely by the action of the nervous system but also by chemical substances, the result of the activity of certain organs. To these chemical substances, as already stated, the name of hormones has been given.
The hormone which has been most thoroughly investigated is adrenalin, a perfectly definite chemical compound consisting of a secondary alcohol linked to a benzene ring. It is a product of the central or medullary part of the suprarenal bodies. The medullary part of these organs is developed from the sympathetic part of the nervous system, and adrenalin acts as a stimulant to the terminations of the sympathetic nerves which spring from the thoracoabdominal region. These nerves control the small arteries, and the main action of adrenalin is to cause a powerful contraction of these vessels, and as a result a great rise in the arterial blood pressure. For this purpose it is now largely used in medicine. The constant supply of adrenalin in small quantities seems to play an important part in keeping up the tone of the blood vessels, and when, as a result of disease of the suprarenals, the supply is cut off a serious train of symptoms supervenes.
Allied to adrenalin is a hormone derived from the pituitary body. This also causes a constriction of the small arteries except those of the kidney, which it dilates. An increased flow of urine is produced.
In the thyroid gland a substance, iodothyrin, is constantly being produced, and this appears to exercise a stimulating action on the rate of chemical exchange in the various tissues. Under its administration the waste of both proteins and fats is increased. When the thyroid is removed or destroyed by disease a condition of decreased chemical change and mental sluggishness results, accompanied often by nervous tremors.
A difficulty in explaining these symptoms is caused by the fact that in the thyroid are imbedded four small parathyroids, and it is possible that these produce a special hormone. It has been suggested that this exercises a particular influence upon the nervous system, but further evidence is wanting.
The well-known effects of removal of the ovaries or testes on the development and character of an animal is due to the absence of the special hormone or hormones of these structures. These hormones appear to be produced, in the case of the testes at least, not in the true genital cells, but in the intermediate cells, since it has been found that ligature of the duct, which leads to destruction of the genital cells, does not abolish the development of the sexual characters of the animal.
There is growing evidence that from the ovaries different hormones may be produced in varying amounts which play an important part in regulating the phenomena of sexual life.
The thymus gland is a structure lying in the front of the neck, which is best developed at the time of birth, grows very slowly after birth, and atrophies when the age of puberty is reached. In castrated male animals it continues to grow and persists throughout life. There is some evidence that it may exercise some effect upon the growth of the testes, probably by hormone action.

Pancreas

Within recent years it has been shown that the internal secretion of this organ plays a very important part in the metabolism of sugar. When the organ is completely extirpated the animal becomes diabetic, i.e. sugar appears in the urine and the animal emaciates. How the internal secretion effects the combustion of the sugar is not yet known. Some workers hold that the action of the pancreatic internal secretion is to control the sugar formation in the various sugar-forming organs, of which the liver is the chief, others that it dominates the utilization of sugar as a source of energy by the muscles.
These are some of the best-known examples of the way in which the products of the activity of one organ modify the functions of other organs. In all probability many more examples of hormone action will be discovered, and it will be found that it plays probably even a more important part than the nervous system in the coordination of function in the animal.
Other factors, besides these already dealt with, play a part in modifying the various metabolic processes, as age, temperature, climate, &c. Very little, however, is definitely known about these various factors.
Water and inorganic salts are quite as essential for the well-being of the body as the energy-yielding proteins, carbohydrates and fats. They, however, probably undergo little or no change in the body; they are excreted pretty much in the same form in which they are ingested. Although they are not subjected to any very great change yet they are of immense importance. No animal tissue can carry on its work in the absence of the various salts. Many experiments have been carried out in which animals have been fed on food as free from salts as possible, and, although the food was much in excess of the energy requirements, yet all these animals died, whereas other animals to which similar food with salts was given throve well. The most important acids are hydrochloric and phosphoric, and the most important bases sodium of potassium. Calcium and magnesium are also of importance, especially where bone formation is taking place. Another element of really vital importance is iron, which is required for the formation of haemoglobin.
VI. Excretion While we know comparatively little of the intermediate stages in the breakdown of the food constituents, and more particularly of the protein moiety, our knowledge of the final products of the metabolic changes excreted is fairly full. The urine is the main channel of excretion for the nitrogenous waste products. C02, arising for the most part frdm the metabolism of carbohydrates and fats, is excreted mainly through the lungs. Water is excreted by the lungs, the kidneys and the skin.
So far no entirely satisfactory explanation has been given of how a fluid like urine, having an acid reaction and containing about one hundred times as much urea and generally more than twice as much sodium chloride as the blood, is formed in the kidneys. The urine is a yellowish fluid which varies greatly in its depth of colour, from pale amber to a deep brown. It has a specific gravity of about 1020, varying with the percentage of solids in solution, and it usually has an acid reaction. It is a fluid of complex character, containing, as already mentioned, practically all the waste nitrogen of the body. Among the principal organic substances present are urea, ammonia, purins (uric acid and the so-called purin bases, xanthin, &c.), creatinin, conjugated sulphates, various aromatic bodies and many other substances in small amount, together with the water and inorganic salts.
The following table from Folin gives a good idea of the average composition of the urine as regards the nitrogen-containing constituents, and its variation according to the nature of the diet when this is free of creatin creatinin and the precursors of the purins: - Urea, which forms the chief nitrogenous constituent, amounting on an ordinary diet to about 30 grms. per diem, is for the most part formed in the liver, from ammonia obtained either directly from the blood after absorption from the intestine, or resulting from the denitrification of the amino acids. It may also arise in part from the diamino acids and from uric acid.
Ammonia is present in the form of ammonium salts, and forms about 4% of the total urinary nitrogen. It may exceed this amount under certain conditions, for the most part pathological. The ammonia is utilized by the body to neutralize acids which arise during the various metabolic processes.
Nitrogen-rich Diet.
Nitrogen-poor Diet.
Total nitrogen.. .
14.8-18.2 grms. per day
4.8- 8 o grms. per day
Urea nitrogen.. .. .
86.3-89.4% of total
62.0-80.4% of total
Ammonia nitrogen.. .
3.3- 5.1%
4.2-11.7% „
Creatinin nitrogen
3.2- 4.5% ,,
5.5-11-1% „
Uric acid nitrogen.. .
0.5- I o % '„
I.2- 2.4% „
Undetermined nitrogen. .
2.7- 5.3%
4.8-14.6% „
Purins (uric acid, xanthin, hypoxanthin, &c.) are all members of a series which have as their common nucleus a body which E. Fischer called purin. The most important member of this series is uric acid. It forms about 2% of the total urinary nitrogen. Recent work has shown that it has two quite definite sources of origin: (I) from ingested food containing the precursors, and (2) from the tissue metabolism. The first is known as the exogenous source, anct the second as the endogenous. This acid is chemically known as trioxy-purin, and may be regarded as the union of two urea molecules with a three-carbon chain fatty acid. All the uric acid formed in the body is not excreted as such, part being, as already mentioned, converted into urea. The amount which is converted into urea varies with the species of animal. In man, Burian and Schur state that one half of the total amount is so converted. Some workers, like Wiener, hold that uric acid may be synthesized in the body, but while this is undoubtedly so in the case of the bird, in the mammal it has not been definitely established. The other chief purin bodies present in urine are xanthin and hypoxanthin, purins less oxidized than uric acid; the first is a dioxypurin, and the second is a monoxypurin. The main source of total purin supply would seem to be muscle metabolism. The mother substances from which all are derived in the body are the nucleins. These complex bodies are apparently first broken down by enzyme action to aminopurins. These in their turn have their amino groups split off, and then, according to the degree of oxidation, the different purin bodies are formed.

Creatinin

The physiological significance of this substance is as yet unknown. The daily excretion varies little with the character of the diet, provided, of course, that the diet be creatin creatinin free. It appears to be proportional to the muscular development and muscular activity of the individual. Hence it would seem to be derived from the creatin of muscle, a substance which is very readily changed into creatinin outside the body. In the body the conversion of creatin into creatinin seems to be strictly limited, and hence when creatin is taken in flesh in the food it tends to appear as such in the urine. It would seem that it is either in great part decomposed in the body into what we do not at present know or that, as suggested by Folin, it may be used as a specialized food. Whatever its source, after urea and ammonia it is one of the most important nitrogenous substances excreted, the daily excretion being about 1.5 grms.
The sulphur excreted in the urine comes chiefly from the sulphur of the protein molecule. It is excreted in various forms. (1) As the ordinary preformed sulphates, that is, sulphur in the form of sulphuric acid combined with the ordinary bases. (2) As ethereal sulphates, that is, in combination with various aromatic substances like phenol, indol, &c. (3) In the form of so-called neutral sulphur in such substances as cystin, which are intermediate products in the complete oxidation of sulphur.
Phosphorus appears linked to the alkalis and alkaline earths as phosphoric acid. A very small part of the phosphoric acid may be eliminated in organic combination such as the glycero-phosphates, &c.
Sodium (mostly as sodium chloride), potassium, calcium and magnesium are the common bases present in the urine.
The lungs are the important channel of excretion for the waste product of carbon metabolism CO 2 (see RESPIRATORY SYSTEM); and also a very important channel for the excretion of water. As regards the skin, the sweat carries off a large amount of the water, but it is difficult to determine the total amount. It has been estimated that about 500 c.c. is excreted per diem under normal conditions. Sweat contains salts, chiefly sodium chloride, and organic waste products. Of the organic solids excreted from this source urea forms the most important under normal conditions. Under pathological conditions, especially when there is interference with free renal action, the amount of nitrogenous waste excreted may become quite important. There is also a small amount of CO 2 excreted by this channel. (D. N. P.; E. P. C.)


Wikibooks

Up to date as of January 23, 2010
(Redirected to Metabolomics/Nutrition article)

From Wikibooks, the open-content textbooks collection

< Metabolomics
Metabolomics Project Logo.jpg
Back to Previous Chapter: Computational Modeling of Metabolic Control
Next Chapter: Databases

Nutrition and Metabolomics

Nutrition, Metabolomics, and Disease


Simple English

File:Healthy eating
Healthy eating pyramid per Harvard School of Public Health
Nutrition provides the cells of an organism with food, in a form they can use. Organisms need food to be able to keep their bodies working properly. They also need food to be able to do certain things.

Different organisms have different food requirements, and they eat different things in order to meet those requirements. Animals that do not eat meat, for example, will have to get certain nutrients like protein from other foods.

Other pages

Error creating thumbnail: sh: convert: command not found

Retrieved from "http://yak.rapint.com/wiki/Nutrition"

Citable sentences

Up to date as of December 22, 2010

Here are sentences from other pages on Nutrition, which are similar to those in the above article.








Got something to say? Make a comment.
Your name
Your email address
Message
Please enter the solution to case below
12+8=