Nutrition

Nutrition is a science that examines 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.

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.

Many common threats 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

Nutrition science investigates 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 cannot 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 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.

Nutrients

Main article: Nutrient

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

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.

According to the United Nations World Health Organization (WHO: 1996), more than starvation the real challenge in developing nations today is malnutrition-the deficiency of micronutrients (vitamins, minerals and essential amino acids) that no longer allows the body to ensure growth and maintain its vital functions.

Carbohydrates

Main article: Carbohydrate

kcal/gram: 4^[1]

Carbohydrates may be classified as monosaccharides, disaccharides, or polysaccharides by the number of sugar units they contain. Monosaccharides contain 1 sugar unit, disaccharides contain 2, and polysaccharides contain 3 or more. Polysaccharides are often referred to as complex carbohydrates because they are long chains of sugar units, whereas monosaccharides and disaccharides are simple carbohydrates. The difference is important to nutritionists because complex carbohydrates take longer to metabolize since their sugar units are processed one-by-one off the ends of the chains. Simple carbohydrates are metabolized quickly and thus raise blood sugar levels more quickly resulting in rapid increases in blood insulin levels.

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 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. 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 a 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).

Protein

Main article: Protein in nutrition

kcal/gram: 4^[1]

Protein is composed of amino acids, that are body's structural (muscles, skin, hair etc.) materials. 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. Dietary sources of protein include meats, eggs, grains, legumes, and dairy products such as milk and cheese. Proteins can be converted into carbohydrates through a process called gluconeogenesis.

Fat

Main article: Fat

kcal/gram: 9^[1]

Fats are composed of fatty acids, long carbon/hydrogen chains bonded to a glycerol. Fat may be classified as saturated or unsaturated. Saturated fats have all of their carbon atoms bonded to hydrogen atoms, whereas unsaturated fats have some of their carbon atoms double-bonded in place of a hydrogen atom. Generally, saturated fat is solid at room temperature while unsaturated fat is a liquid. Unsaturated fats may be further classified as mono-unsaturated (one double-bond) or poly-unsaturated (many double-bonds). Trans fats are saturated fats which are typically created from unsaturated fat by adding the extra hydrogen atoms in a process called hydrogenation (also called hydrogenated fat).

Most fatty acids are non-essential, meaning the body can produce them as needed, however, at least two fatty acids are essential and must be consumed in the diet. 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).

Vitamins

Main article: Vitamin

kcal/gram: 0

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.^[2]

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.

Minerals

Main article: Dietary mineral

kcal/gram: 0

Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen which are present in common organic molecules. The term "mineral" is archaic, since the intent of the definition is to describe ions, not chemical compounds or actual minerals. Some dietitians recommend that these heavier elements should be supplied by ingesting specific foods (that are enriched in the element(s) of interest), compounds, and sometimes including even minerals, such as calcium carbonate. Sometimes these "minerals" come from natural sources such as ground oyster shells. Sometimes minerals are added to the diet separately from food, such as mineral supplements, the most famous being iodine in "iodized salt."

Macrominerals

A variety of elements are required to support the biochemical processes, many play a role as electrolytes or in a structural role.^[3] In Human nutrition, the dietary bulk "mineral elements" (RDA > 200 mg/day) are in alphabetical order (parenthetical comments on folk medicine perspective):

• Calcium (for muscle and digestive system health, builds bone, neutralizes acidity, clears toxins, helps blood stream)
• Chloride
• Magnesium required for processing ATP and related reactions (health, builds bone, causes strong peristalsis, increases flexibility, increases alkalinity)
• Phosphorus required component of bones (see apatite) and energy processing and many other functions (bone mineralization)^[4]
• Potassium required electrolyte (heart and nerves health)
• Sodium electrolyte
• Sulfur for three essential amino acids and many proteins and cofactors (skin, hair, nails, liver, and pancreas health)

Trace minerals

A variety of elements are required in trace amounts, unusually because they play a role in catalysis in enzymes.^[5] Some trace mineral elements (RDA < 200 mg/day) are (alphabetical order):

• Cobalt required for biosynthesis of vitamin B12 family of coenzymes
• Copper required component of many redox enzymes, including cytochrome c oxidase
• Chromium required for sugar metabolism
• Iodine required for the biosynthesis of thyroxin
• Iron required for many proteins and enzymes, notably hemoglobin
• Manganese (processing of oxygen)
• Molybdenum required for xanthine oxidase and related oxidases
• Nickel present in urease
• Selenium reqiured for peroxidase (antioxidant proteins)
• Vanadium (There is no established RDA for vanadium. No specific biochemical function has been identified for it in humans, although vanadium is found in lower organisms.)
• Zinc required for several enzymes such as carboxypeptidase, liver alcohol dehydrogenase, carbonic anhydrase. Zinc is pervasive.

Iodine is required in larger quantities than the other trace minerals in this list and is sometimes classified with the bulk minerals. Sodium is not generally found in dietary supplements, despite being needed in large quantities, because the ion is very common in food.

Fibre

Main article: Dietary fiber

Dietary fiber consists mainly of cellulose that is indigestible because we do not have enzymes to digest it. Fruits and vegetables are rich in dietary fiber.

Importance of dietary fiber:

• provides bulk to the intestinal contents
• stimulates peristalsis (rhythmic muscular contractions passing along the digestive tract)

Lack of dietary fiber in the diet leads to constipation (failure to pass motions).

Water

Main article: Drinking water

kcal/gram: 0

About 70% of the non-fat mass of the human body is made of water. To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

It is not clear how much water intake is needed by healthy people, although some experts assert that 8%u201310 glasses of water (approximately 2 liters) daily is the minimum to maintain proper hydration.^[6] The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source.^[7] There are other myths such as the effect of water on weight loss and constipation that have been dispelled.^[8] Original recommendation for water intake 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."^[9] The latest dietary reference intake report by the United States National Research Council in general recommended (including food sources): 2.7 liters of water total for women and 3.7 liters for men.^[10] Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. According to the Institute of Medicine%u2014who recommend that, on average, women consume 2.2 litres and men 3.0 litres%u2014this 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.^[11]

For those who have healthy kidneys, it is rather difficult to drink too much water, 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.

Normally, about 20 percent of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath.

Antioxidants

Main article: Antioxidant

kcal/gram: 0^{[citation needed]}

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). Phytochemicals (Section Below) and their subgroup polyphenols comprise of the majority of antioxidants, some 4,000 known, and therefore there is much overlap. 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.

Phytochemicals

Main article: Phytochemical

A growing area of interest is the effect upon human health of trace chemicals, collectively called phytochemicals. These antioxidant 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).^[12] Less rigorous studies have proposed a correlation between zeaxanthin intake and cataracts.^[13] 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.^[14] 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. 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.^[15] 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. 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[16]
isothiocyanates	cruciferous vegetables	cancer prevention
monoterpenes	citrus peels, essential oils, herbs, spices, green plants, atmosphere[17]	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

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.

Sports nutrition

Main article: Sports nutrition

Protein

The protein requirements of athletes, once the source of great controversy, has settled into a current consensus. Sedentary people and recreational athletes^[18] have similar protein requirements, about 1 gram of protein per kilogram of body mass. These needs are easily met by a balanced diet containing about 70 grams of protein for a 70 kg (150 pound) man or 60 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 2 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 2 to 3 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.

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.^{[citation needed]} 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.^{[citation needed]} 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, 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.^[19] 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.

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]} 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.^{[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. Meeting energy needs can help improve performance during the sport, as well as improve overall strength and endurance.

Longevity

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. One study in China found some regions had essentially no cancer or heart disease, while in other areas they reflected %u201Cup to a 100-fold increase%u201D coincident with diets that were found to be entirely plant-based to heavily animal-based, respectively.^[20] 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 %u201CWestern%u201D diseases possibly because their diets are rich in vegetables, fruits and whole grains.^[21]

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 is 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."

Note that cancer is now common in developing countries. According a study by the International Agency for Research on Cancer: %u201CIn 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.%u201D Lung cancer rates are rising rapidly in poorer nations because of increased use of tobacco. Developed countries %u201Ctended to have cancers linked to affluence or a "Western lifestyle" %u2013 cancers of the colon, rectum, breast and prostate %u2013 that can be caused by obesity, lack of exercise, diet and age.%u201D^[22]

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:

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