Nutrition

The updated USDA food pyramid, published in 2005, is a general nutrition guide for recommended food consumption.

Nutrition is a science that studies the relationship between diet and health. Dietitians are health professionals who specialize in this area of study, and are trained to provide safe, evidence-based dietary advice and interventions. In the U.S., Dietitians are registered with the American Dietetic Association and are only able to use the label "Dietitian" when they have met strict, specific educational and experiential prerequisites and passed a national registration examination. Anyone may call themselves a Nutritionist,including unqualified personnel, as this term is unregulated.

Deficiencies, excesses and imbalances in diet can produce negative impacts on health, which may lead to diseases such as cardiovascular disease, diabetes, scurvy, obesity or osteoporosis, as well as psychological and behavioral problems. Moreover, excessive ingestion of elements that have no apparent role in health, (e.g. lead, mercury, PCBs, dioxins), may incur toxic and potentially lethal effects, depending on the dose.

Many common diseases and their symptoms can often be prevented or alleviated with better nutrition. The science of nutrition attempts to understand how and why specific dietary aspects influence health.

Overview

The purposes of nutrition science is to explain metabolic and physiological responses of the body to diet. With advances in molecular biology, biochemistry, and genetics, nutrition science is additionally developing into the study of metabolism, which seeks to disconnect diet and health through the lens of biochemical processes.

The human body is made up of chemical compounds such as water, amino acids (proteins), fatty acids (lipids), nucleic acids (DNA/RNA), and carbohydrates (e.g. sugars and fiber). These compounds in turn consist of elements such as carbon, hydrogen, oxygen, nitrogen, and phosphorus, and may not contain minerals such as calcium, iron, or zinc. Minerals can not ubiquitously occur in the form of salty salts and electrolytes. All of these chemical compounds and elements occur in various forms and combinations (e.g. hormones/vitamins, phospholipids, hydroxyapatite), both in the human body and in organisms (e.g. plants, animals) that humans eat.

The human body necessarily comprises the elements that it eats and absorbs into the bloodstream. The digestive system, except in the unborn fetus, participates in the first step which makes the different chemical compounds and elements in food available for the trillions of cells of the body. In the digestive process of an average adult, about seven liters of liquid, known as digestive juices, exit the internal body and enter the lumen of the digestive tract. The digestive juices help break chemical bonds between ingested compounds as well as modulate the conformation and/or energetic state of the compounds/elements. However, many compounds/elements are absorbed into the bloodstream unchanged, though the digestive process helps to release them from the matrix of the foods where they occur. Any unabsorbed matter is excreted in the feces. But only a minimal amount of digestive juice is eliminated by this process; the intestines reabsorb most of it; otherwise the body would rapidly dehydrate; (hence the devastating effects of persistent diarrhea).

Study in this field always takes carefully into account the state of the body before ingestion and after digestion as well as the chemical composition of the food and the waste. Comparing the waste to the food can determine the specific types of compounds and elements absorbed by the body. The effect that the absorbed matter has on the body can be determined by finding the difference between the pre-ingestion state and the post-digestion state. The effect may only be discernible after an extended period of time in which all food and ingestion must be exactly regulated and all waste must be analyzed. The number of variables (e.g. 'confounding factors') involved in this type of experimentation is very high. This makes scientifically valid nutritional study very time-consuming and expensive, and explains why a proper science of human nutrition is rather new.

In general, eating a variety of fresh, whole (unprocessed) plant foods has proven hormonally and metabolically favourable compared to eating a monotonous diet based on processed foods. In particular, consumption of whole plant foods slows digestion and provides higher amounts and a more favourable balance of essential and vital nutrients per unit of energy; resulting in better management of cell growth, maintenance, and mitosis (cell division) as well as regulation of blood glucose and appetite. A generally more regular eating pattern (e.g. eating medium-sized meals every 2 to 3 hours) has also proven more hormonally and metabolically favourable than infrequent, haphazard food intake.

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. 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. 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.

Agriculture developed about 10,000 years ago in multiple locations throughout the world, providing grains such as wheat, rice, and maize, with staples such as bread and pasta. 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.

Antiquity through Enlightenment

• 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.
• c. 475 BC: Anaxagoras states that food is absorbed by the human body and therefore contained "homeomerics" (generative components), thereby deducing the existence of nutrients.
• c. 400 BC: Hippocrates says, "Let food be your medicine and medicine be your food."
• 1500s: Scientist and artist Leonardo da Vinci compared metabolism to a burning candle.
• 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.
• 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.
• 1790: George Fordyce recognized calcium necessary for fowl survival.

Modern era through 1941

• 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.
• 1816: François Magendie discovers 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.
• 1840: Justus Liebig discovers the chemical makeup of carbohydrates (sugars), fats (fatty acids) and proteins (amino acids.)
• 1860s: Claus Bernard discovers that body fat can be synthesised from carbohydrate and protein, showing that the energy in blood glucose can be stored as fat or as glycogen.
• Early 1880s: Kanehiro Takaki observed that Japanese sailors developed beriberi (or endemic neuritis, a disease causing heart problems and paralysis) but British sailors did not. Adding milk and meat to Japanese diets prevented the disease.
• 1896: Baumann observed iodine in thyroid glands.
• 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. 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.
• Early 1900s: Carl Von Voit and Max Rubner independently measure caloric energy expenditure in different species of animals, applying principles of physics in nutrition.
• 1906: Wilcock and Hopkins showed that the amino acid tryptophan was necessary for the survival of mice. Gowland Hopkins recognized "accessory food factors" other than calories, protein and minerals, as organic materials essential to health but which the body cannot synthesise.
• 1907: Stephen M. Babcock and Edwin B. Hart conduct the Single-grain experiment. This experiment runs through 1911.
• 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.
• 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.
• 1919: Sir Edward Mellanby incorrectly identified rickets as a vitamin A deficiency, because he could cure it in dogs with cod liver oil.
• 1922: McCollum destroys the vitamin A in cod liver oil but finds it still cures rickets, naming vitamin D
• 1922: H.M. Evans and L.S. Bishop discover vitamin E as essential for rat pregnancy, originally calling it "food factor X" until 1925.
• 1925: Hart discovers trace amounts of copper are necessary for iron absorption.
• 1927: Adolf Otto Reinhold Windaus synthesizes vitamin D, for which he won the Nobel Prize in Chemistry in 1928.
• 1928: Albert Szent-Gyorgyi isolates 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-Gyorgyi concurrently elucidates much of the citric acid cycle.
• 1930s: William Cumming Rose identifies essential amino acids, necessary protein components which the body cannot synthesize.
• 1935: Underwood and Marston independently discover the necessity of cobalt.
• 1936: Eugene Floyd Dubois shows that work and school performance are related to caloric intake.
• 1938: The chemical structure of vitamin E is discovered by Erhard Fernholz, and it is synthesised by Paul Karrer.
• 1940 UK institutes rationing according to nutritional principles drawn up by Elsie Widdowson and others
• 1941: The first Recommended Dietary Allowances (RDAs) were established by the National Research Council.

Recent

• 1992 The U.S. Department of Agriculture Introduces Food Guide Pyramid
• 2002 Study shows relation between nutrition and violent behavior
• 2005 Obesity may be caused by adenovirus in addition to bad nutrition

Nutrition and health

There are six main classes of nutrients that the body needs: carbohydrates, proteins, fats, vitamins, minerals, and water. It is important to consume these six nutrients on a daily basis to build and maintain healthy bodily function.

Poor health can be caused by an imbalance of nutrients, either an excess or deficiency, which, in turn, affects bodily functions cumulatively. Moreover, because most nutrients are involved in cell-to-cell signalling (e.g. as building blocks or as part of a hormone or signalling cascades), deficiency or excess of various nutrients affects hormonal function indirectly. Thus, because they largely regulate the expression of genes, hormones represent a link between nutrition and how our genes are expressed, i.e. our phenotype. The strength and nature of this link are continually under investigation, but recent observations have demonstrated a pivotal role for nutrition in hormonal activity and function and therefore in health.

Essential and non-essential amino acids

The body requires amino acids to produce new body protein (protein retention) and to replace damaged proteins (maintenance) that are lost in the urine. In animals amino acid requirements are classified in terms of essential (an animal cannot produce them) and non-essential (the animal can produce them from other nitrogen containing compounds) amino acids. Consuming a diet that contains adequate amounts of essential (but also non-essential) amino acids is particularly important for growing animals, who have a particularly high requirement.

Vitamins

Mineral and/or vitamin deficiency or excess may yield symptoms of diminishing health such as goitre, scurvy, osteoporosis, weak immune system, disorders of cell metabolism, certain forms of cancer, symptoms of premature aging, and poor psychological health (including eating disorders), among many others.

As of 2005, twelve vitamins and about the same number of minerals are recognized as "essential nutrients", meaning that they must be consumed and absorbed - or, in the case of vitamin D, alternatively synthesized via UVB radiation - to prevent deficiency symptoms and death. Certain vitamin-like substances found in foods, such as carnitine, have also been found essential to survival and health, but these are not strictly "essential" to eat because the body can produce them from other compounds. Moreover, thousands of different phytochemicals have recently been discovered in food (particularly in fresh vegetables), which have many known and yet to be explored properties including antioxidant activity (see below). Other essential nutrients include essential amino acids, choline and the essential fatty acids.

Fatty acids

In addition to sufficient intake, an appropriate balance of essential fatty acids - omega-3 and omega-6 fatty acids - has been discovered to be crucial for maintaining health. Both of these unique "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins which function as hormones. The omega-3 eicosapentaenoic acid (EPA) (which can be made in the body from the omega-3 essential fatty acid alpha-linolenic acid (LNA), or taken in through marine food sources), serves as building block for series 3 prostaglandins (e.g. weakly-inflammation PGE3). The omega-6 dihomo-gamma-linolenic acid (DGLA) serves as building block for series 1 prostaglandins (e.g. anti-inflammatory PGE1), whereas arachidonic acid (AA) serves as building block for series 2 prostaglandins (e.g. pro-inflammatory PGE 2). Both DGLA and AA are made from the omega-6 linoleic acid (LA) in the 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, which partly explains the importance of omega-3/omega-6 balance for cardiovascular health. In industrialised societies, people generally consume large amounts of processed vegetable oils that have reduced amounts of essential fatty acids along with an excessive amount of omega-6 relative to omega-3.

The rate of conversions of omega-6 DGLA to AA largely determines the production of the respective 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). Because different types and amounts of food eaten/absorbed affect insulin, glucagon and other hormones to varying degrees, not only the amount of omega-3 versus omega-6 eaten but also the general composition of the diet therefore determine health implications in relation to essential fatty acids, inflammation (e.g. immune function) and mitosis (i.e. cell division).

Sugars

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. Although the association between overfatness 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 overfat 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. 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. 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. In addition, reduced leptin signalling to the brain may reduce leptin's normal effect to maintain an appropriately high metabolic rate.

There is debate about how and to what extent different dietary factors -- e.g. 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).

Antioxidants are another recent discovery. As cellular metabolism/energy production requires oxygen, potentially damaging (e.g. mutation causing) compounds known as radical oxygen species or free radicals form as a result. For normal cellular maintenance, growth, and division, these free radicals must be sufficiently neutralized by antioxidant compounds, some produced by the body with adequate precursors (glutathione, Vitamin C in most animals) and those that the body cannot produce may only be obtained through the diet through 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). 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. 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. 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.

Intestinal bacterial flora

Main article: Gut flora

It is now also known that the human digestion system contains a population of a range of bacteria and yeast such as Bacteroides, L. acidophilus and E. coli which are essential to digestion, and which are also affected by the food we eat. Bacteria in the gut fulfill a host of 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; and defending against some diseases.

Phytochemicals

Blackberries are a source of polyphenol antioxidants

A growing area of interest is the effect upon human health of trace chemicals, collectively called phytochemicals, nutrients typically found in edible plants, especially colorful fruits and vegetables (see Whole Foods Diet, below). Unlike the anecdotal and sometimes specious nutritional claims of medicinal herbs and compounds, 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). Less rigorous studies have proposed a correlation between zeaxanthin intake and cataracts. 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.

Another caretenoid, 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. 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. For example, several studies have correlated high levels of zeaxanthin intake with roughly a 50% reduction in AMD. The difficulties in demonstrating causative properties and in applying the findings to human diet, however, are similarly enormous. The standard for rigorous proof of causation in medicine is the double-blind study, a time-consuming, difficult and expensive process, especially in the case of preventative medicine. While new drugs must undergo such rigorous testing, pharmaceutical companies have a financial interest in funding rigorous testing and may recover the cost if the drug goes to market. No such commercial interest exists in studying chemicals that exist in orange juice and spinach, making funding for medical research difficult to obtain.

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. 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. At the most basic level, the question "should you eat eggs?" 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. Such sauces, however, tend to have high amounts of salt, sugar, other substances a person may wish or even need to avoid.

The following table of phytochemical groups and common sources, arranged by family, is taken in part from the Wikipedia article on phytochemicals.

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
isothiocyanates	cruciferous vegetables	cancer prevention
monoterpenes	citrus peels, essential oils, herbs, spices, green plants, atmosphere	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, Anti-inflammatory
capsaicinoids	all capiscum (chile) peppers	topical pain relief, cancer prevention, cancer cell apoptosis

Nutrition and sports

Protein

The protein requirements of athletes, once the source of great controversy, has settled into a current consensus. Sedentary people and recreational athletes have similar protein requirements, about .8 to 1 gram of protein per kilogram of body mass. These needs are easily met by a balanced diet containing about 56 grams of protein for a 70 kg (150 pound) man or 46 grams of protein for a 60 kg (130 pound) woman.

People who exercise at greater intensity, and especially those whose activity grows muscle bulk, have significantly higher protein requirements. According to Clinical Sports Nutrition (see footnote above), active athletes playing power sports (such as football), those engaged in muscle-development training, and elite endurance athletes, all require approximately 1.6 grams of protein per day per kilogram of body weight, roughly double that of a sedentary persons. Older athletes seeking primarily to maintain developed muscle mass require 1 to 1.2 g/day/kg.

Protein intake in excess of that required to build muscle (and other) tissue is broken-down by gluconeogenesis to be used as energy or stored as fat.

Excess protein consumption in the absence of alkalizing mineral intake (usually from fruits and vegetables) may leads to low grade acididosis in which calcium and glutamine may be leached from bone and muscle respectively to keep the blood pH steady. Where gross caloric intake is adequate, however, a more benign form of ketosis generally results. (This should not be confused with the very harmful ketoacidosis, seen primarily in diabetics and alcoholics.) The overall effect on physical health of a low-carbohydrate diet -- especially concerning blood lipids, bone mass, potential osteoporosis, and possible strain on the liver and kidneys -- is the subject of an impassioned debate, which has not been resolved. All reputable authories agree, however, that excess protein consumption requires additional water intake to prevent dehydration.

The most recent evidence appears to support the beneficial nature of a high-protein, low-carbohydrate diet. A large randomized study at Stanford University found that women following such a diet "lost more weight and experienced more favorable overall metabolic effects at 12 months" than in other diets. The study followed 311 pre-menopausal, non-diabetic women, age 25-50. The women lost significantly more weight (mean 4.7 kg) on the Atkins diet than on 3 higher-carbohydrate diets (LEARN 2.6 kg, Ornish 2.2 kg, and Zone 1.6 kg), without increasing cardiovascular risks. Changes in HDL cholesterol, triglycerides, and mean blood pressure significantly favored Atkins over the other three diets. The authors concluded that "concerns about adverse metabolic effects of the Atkins diet were not substantiated within the 12-month study period."

Water and Salts

Maintaining hydration during periods of physical exertion is key to good 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. It is recommended that an athlete drink about 400-600 mL 2-3 hours before activity, during exercise he or she should drink 150-350mL every 15 to 20 minutes and after exercise that he or she replace sweat loss by drinking 450-675 mL for every 0.5 kg body weight loss during activity. Some studies have shown that an athlete that drinks before they feel thirsty stays cooler and performs better than one who drinks on thirst cues, although recent studies of such races as the Boston Marathon have indicated that this recommendation can lead to the problem of overhydration. 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.

Excess water intake, without replenishment of sodium and potassium salts, leads to hyponatremia, also called water intoxication at more dangerous levels. A well-publicized case occurred in 2007, when Jennifer Strange died while participating in a water-drinking contest. 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.

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. When glycogen is not present in muscles, the muscle cells perform anaerobic respiration producing lactic acid, which is responsible for fatigue and burning sensation, and post exercise stiffness in muscles. 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. Meeting energy needs can help improve performance during the sport, as well as improve overall strength and endurance.

Nutrition and longevity

Calorie restriction

Lifespan may be somehow related to the amount of food energy consumed. A pursuit of this principle of caloric restriction followed, involving research into longevity of those who reduced their food energy intake while attempting to optimize their micronutrient intake. Perhaps not surprisingly, some people found that cutting down on food reduced their quality of life so considerably as to negate any possible advantages of lengthening their lives. However, a small set of individuals persist in the lifestyle, going so far as to monitor blood lipid levels and glucose response every few months. See Calorie Restriction Society.

Underlying this research was the hypothesis that oxidative damage was the agent which accelerated aging, and that aging was retarded when the amount of carbohydrates (and thereby insulin release) was reduced through dietary restriction.

However, recent research has produced increased longevity in animals (and shows promise for increased human longevity) through the use of insulin uptake retardation. This was done through altering an animal’s metabolism to allow it to consume similar food-energy levels to other animals, but without building up fatty tissue.

This has set researchers off on a line of study which presumes that it is not low food energy consumption which increases longevity. Instead, longevity may depend on an efficient fat processing metabolism, and the consequent long term efficient functioning of our organs free from the encumbrance of accumulating fatty deposits. Thus, longevity may be related to maintained insulin sensitivity. However, several other factors including low body temperature seem to promote longevity also and it is unclear to what extent each of them contribute.

Antioxidants have recently come to the forefront of longevity studies which have included the Food and Drug Administration and Brunswick labs.

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. 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. In contrast, diseases of affluence like cancer and heart disease are common throughout the United States. Adjusted for age and exercise, large regional clusters of people in China rarely suffered from these “Western” diseases because their diets are rich in vegetables, fruits and whole grains.

The United Healthcare/Pacificare nutrition guideline recommends a whole plant food diet, and recommends using protein only as a condiment with meals. A National Geographic (November 2005) cover article, titled 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 if up to you." In common with all three groups is to "Eat fruits, vegetables, and whole grains."

The National Geographic article noted that a 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. And it found that not eating red meat had been helpful to avoid both cancer and heart disease."

Note that cancer is now common in developing countries. According 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.”

The French "paradox"

Main article: French paradox

It has been discovered that people living in France live longer. Even though they consume more saturated fats than Americans, the rate of heart disease is lower in France than in North America. A number of explanations have been suggested:

• Reduced consumption of processed carbohydrate and other junk foods;
• Ethnic genetic differences allowing the body to be harmed less by fats;
• Regular consumption of red wine; or
• Living in the South requires the body to produce less heat, allowing a slower, and therefore healthier, metabolic rate.

However, a growing number of French health researchers doubt the theory that the French are healthier than other populations. Statistics collected by the WHO 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.

Nutrition, industry and 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. 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. But some of the (new) food processing technologies undoubtedly have downfalls as well.

Modern separation techniques such as milling, centrifugation, and pressing have enabled upconcentration 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 upconcentration 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. 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. Nonetheless, processed foods tend to have an inferior nutritional profile than do whole, fresh foods, regarding content of both sugar and high GI starches, potassium/sodium, vitamins, fibre, and of intact, unoxidized (essential) fatty acids. In addition, processed foods often contain potentially harmful substances such as oxidized fats and trans fatty acids.

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. There is little doubt that the increasingly widespread application of some modern food processing technologies has contributed to this development. The food processing industry is a major part of modern economy, and as such it is influential in political decisions (e.g. 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. In general, whole, fresh foods have a relatively short shelf-life and are less profitable to produce and sell than are more processed foods. 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.

Nutrition and Learning

Governmental policies

File:Senate-hearing-school-nutrition.jpg

Witnesses give recommendations to the US Senate Agriculture, Nutrition and Forestry Committee on school nutrition and childhood obesity.

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 currently controlled by the US Department of Agriculture. Dietary and exercise 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.

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 nutrition included, stressing the importance of a balanced diet and teaching how to read nutrition labels on packaging. However, in developing countries it is a distant dream; misconceptions, gender bias, ignorance of hygienic conditions, etcetera, are still existing in their full strength.

Nutrition and its effects on the learning process

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. In other words it can help increase a student’s potential to process and retain academic information.

That being said, it could be argued that by working with teachers, policymakers, and (almost most importantly) managed foodservice contractors to mandate improved nutritional content and increased nutritional resources in school cafeterias from primary to university level institutions, we could positively affect student potential to process and retain academic information on an enormous scale.

There is no denying that good nutritional behavior has a considerable impact on a student’s academic achievement. Many reputable organizations have drawn correlations between good nutrition and a learning ability.

>Health and nutrition have been proven to have close links with overall educational success. (Behrman, 1996).

>Currently less than 10% of American college students report that they ate the recommended five servings of fruit and vegetables daily. Better nutrition has been scientifically proven to have a positive effect on both cognitive and spatial memory performance.

>Subjects with elevated blood glucose levels performed better on multiple memory tests.

>Subjects performed better after consuming yogurt than caffeine free diet soda or confections (i.e. yogurt)

Scientific evidence illustrating a link between memory function and proper nutrition are far from novel.

>Nutritional deficiencies have been proven to have a negative effect on learning behavior in mice as far back as 1951.

>“Better learning performance … is associated with diet induced effects on learning and memory ability”.

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.”

>91% of college students feel that they are in good health while only 7% eat their recommended daily allowance of fruits and vegetables.

>Nutritional education is an effective and workable model in a higher education setting.

>More “engaged” learning models that encompass nutrition is an idea that is picking up steam at all levels of the learning cycle .

In conclusion, there is a shocking lack of nutritional awareness in American college students considering the positive long term affect it can have on their learning ability during this crucial period in their development. A combination of an elevated awareness in and the availability of, targeted nutritional information will help to increase the likelihood of good health in a college setting and it’s an attainable goal.

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 beyond a shadow of a doubt that overall intellectual health is closely linked to a person’s diet.

Issues

Challenging issues in modern nutrition include:

"Artificial" interventions in food production and supply:

• Should genetic engineering be used in the production of food crops and animals?
• Are the use of pesticides, and fertilizers damaging to the foods produced by use of these methods (see also organic farming)?
• Are the use of antibiotics and hormones in animal farming ethical and/or safe?

Sociological issues:

• Is it possible to eat correctly on a low income? Is proper nutrition economically skewed? How do we increase access to whole foods in impoverished neighborhoods?
• How do we minimise the current disparity in food availability between first and third world populations (see famine and poverty)?
• How can public advice agencies, policy making and food supply companies be coordinated to promote healthy eating and make wholesome foods more convenient and available?
• Should food stamps be distributed to obese families?
• Do we need nutritional supplements in the form of pills, powders, liquids, etc.?
• How can the developed world promote good worldwide nutrition through minimising import tariffs and export subsidies on food transfers?

Research Issues:

• How do different nutrients affect appetite and metabolism, and what are the molecular mechanisms?
• Can a whole plant food diet, replete with diversity and colors, be instituted and implemented to improve health and reduce medical costs?
• What yet to be discovered important roles do vitamins, minerals, and other nutrients play in metabolism and health?
• Are the current recommendations for intake of vitamins and minerals appropriate?
• How and why do different cell types respond differently to chronically elevated circulating levels of insulin, leptin, and other hormones?
• What does it take for insulin resistance to develop?
• What other molecular mechanisms may explain the link between nutrition and lifestyle-related diseases?
• What role does the intestinal bacterial flora play in digestion and health?
• How essential to proper digestion are the enzymes contained in food itself, which are usually destroyed in cooking (see Living foods diet)?
• What more can we discover through what has been called the phytochemical revolution?

See also

Main list: List of basic nutrition topics

Biology: Digestion Enzyme Dangers of poor nutrition Deficiency Avitaminosis is a deficiency of vitamins. Boron deficiency (medicine) Chromium deficiency Iron deficiency (medicine) Iodine deficiency Magnesium deficiency (medicine) Diabetes Eating disorders Illnesses related to poor nutrition Malnutrition Obesity Childhood obesity Starvation Food: Food (portal) 5 A Day Canada's Food Guide Fast Food Food groups Food guide pyramid Food supplements Fruits Functional food Grains Junk Food Meat Vegetables

Healthy diet: Calorie restriction Dieting Eating Healthy eating pyramid Paleolithic diet Pritikin diet Vegetarian nutrition Vegetarianism Veganism China project Lists: Diets (list) List of food additives List of illnesses related to poor nutrition List of life extension related topics List of publications in nutrition List of unrefined sweeteners Nutrients: Carbohydrates Dietary minerals Essential minerals Dietary supplements Essential nutrients Fat Essential fatty acids Macronutrients Micronutrients Nootropics Nutraceuticals

Phytochemicals Protein Complete protein Essential amino acids Incomplete protein Protein combining Protein in nutrition Vitamins Profession: Dietitian Nutritionist Nutritional Therapist Related topics Main article: Health Auxology Exercise General Fitness Training Health (portal) Life extension Natural Hygiene Orthomolecular medicine Physical fitness

Bibliography

• The Times newspaper, January 31 2004 Could vitamins help delay the onset of Alzheimer’s? by Jerome Burne.
• The Times newspaper February 28, 2004 Autism: I can see clearly now . . . by Simon Crompton
• The Times newspaper March 10, 2004 Work up an Amish appetite by Anne-Celine Jaeger
• William Eaton et al. 2004. Coeliac disease and schizophrenia. British Medical Journal, February 21, 2004.
• Janssen I, Katzmarzyk PT, Ross R. Waist circumference and not body mass index explains obesity-related health risk. Am J Clin Nutr. 2004 Mar;79(3):379-84.
• J Mei, SSC Yeung et al. 2001. High dietary phytoestrogen intake and bone mineral density in postmenopausal women. Journal of Clinical Endocrinology and Metabolism, Vol 86, Iss 11.
• Merritt JC. 2004. Metabolic syndrome: soybean foods and serum lipids. J Natl Med Assoc. Aug;96(8):1032-41.
• Sobczak S, et al. (2004) Lower high-density lipoprotein cholesterol and increased omega-6 polyunsaturated fatty acids in first-degree relatives of bipolar patients Psychol Med. 2004 Jan;34(1):103-12.
• Walter C. Willett and Meir J. Stampfer. 2003. Rebuilding the Food Pyramid. Scientific American January 2003.
• Galdston, I., Human Nutrition Historic and Scientific (New York: International Universities Press, 1960)
• Mahan, L.K. and Escott-Stump, S. eds. (2000) Krause's Food, Nutrition, and Diet Therapy. 10th ed. (Phaladelphia: W.B. Saunders Harcourt Brace)

External links

Professional Dietetic Associations and Resources

• The American Dietetic Association
• The British Dietetic Association
• [http://www.indi.ie/ The Irish Nutrition and Dietetic Institute
• Dietitians of Canada
• The Singapore Nutrition and Dietetics Association
• Dietitians Association of Australia
• New Zealand Dietetic Association
• Nutritional Facts
• Nutrition data
• International Confederation of Dietetic Associations
• American Society for Parenteral and Enteral Nutrition

Other

• Diet, Nutrition and the prevention of chronic diseases by a Joint WHO/FAO Expert consultation (2003)
• UN Standing Committee on Nutrition - In English, French and Portuguese
• USDA Frequently asked questions