Nutrition

From Free net encyclopedia

Image:MyPyramid1.png Nutrition is a science which studies the relationship between diet and states of health and disease. Dieticians are Health professionals who are specialised in this area of expertise. They are also the only highly trained health professionals able to provide safe, evidence based and accurate dietary advise and interventions.

Between the extremes of optimal health and death from starvation or malnutrition, there is an array of disease states that can be caused or alleviated by changes in diet. Deficiencies, excesses and imbalances in diet can produce negative impacts on health, which may lead to diseases such as 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. The science of nutrition attempts to understand how and why specific dietary aspects influence health.

Contents

Overview

The human body comprises chemical compounds such as water, amino acids (proteins), fatty acids (lipids), nucleic acids (DNA/RNA), and carbohydrates (e.g. sugars). These compounds in turn consist of elements such as carbon, hydrogen, oxygen, nitrogen, and phosphorus, and may or may not contain minerals such as calcium, iron, and zinc. Minerals ubiquitously occur in the form of 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 humans eat and absorb 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 litres 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 must take 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) foods has proven hormonally and metabolically favourable compared to eating a monotonous diet based on processed foods. In particular, fresh, whole foods provide 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 of appetite and energy balance. A generally more regular eating pattern (e.g. eating medium-sized meals every 3 to 4 hours) has also proven more hormonally and metabolically favourable than infrequent, haphazard food intake.

History

Humans evolved as omnivorous hunter-gatherers over the past 250,000 years. Early diets were primarily vegetarian with infrequent game meats and fish where available.

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 a ritualistic activity due to efficiency and reliability concerns requiring adherence to strict recipes and procedures, and also contributed to demands for food purity and consistency.

Antiquity through Enlightenment

  • c. 475 BC: Anaxagoras reasoned 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."
  • 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.
  • 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 recognized 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: Claude Bernard discovers that body fat can be synthesised from carbohydrate and protein, showing that the energy in blood glucose can be stored in fat 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 can not synthesise.
  • 1912: Casmir 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 V. 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.
  • 1919: Sir Edward Mellanby incorrectly identified rickets as a vitamin A deficiency, because he could cure it in dogs with cod liver oil. Template:Ref
  • 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 proteins which the body can not 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.
  • 1941: The first Recommended Dietary Allowances (RDAs) were established by the National Research Council.

Recent

Nutrition and Health

Ill health can be caused by an imbalance of nutrients, producing either an excess or deficiency, which in turn affects body functioning cumulatively. Moreover, because most nutrients are, in some way or another, involved in cell-to-cell signalling (e.g. as building block or 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 observations especially in recent years 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 (tocotrienol and tocopherol) 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 Template:Ref.

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 be produced can 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

It is now also known that the human digestion system contains a population of a range of bacteria which are essential to digestion, and which are also affected by the food we eat. The role and significance of the intestinal bacterial flora is under investigation. Both good and bad bacteria inhabit the digestive system. It is estimated that in the Western world, most people are no longer in a homeostatic balance. It is ideal to have 80% good to 20% bad, typically differentiated by gram negative and gram positive staining, respectively; however, in western diets it is more likely to be the other way around. Consuming processed food that are low in nutrients and high in sugar will allow bad bacteria to flourish.

Phytochemicals

A growing area of interest is the effect upon human health of trace chemicals, collectively called phytochemicals. Although technically the term refers to nutrients from edible plants, especially highly colored fruits and vegetables, they are sometimes found in animal products. 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.

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. Template:Ref Less rigorous studies have proposed a correlation between zeaxanthin intake and cataracts. Template:Ref 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. Template:Ref 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. Template:Ref 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.

Probably the best practical solution is to follow mother's advice: eat your fruits and veggies.

Nutrition and sports

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Nutrition is very important for improving sports performance. The most common means to improve performance through diet is the practice of eating large quantities of protein, usually red meat, when attempting to build muscle mass; its efficacy is doubtful, as daily protein intake even on a normal diet usually outweighs the amount of muscle protein which can be synthesized in a day.

To enhance their speed of muscle synthesis, athletes will focus a great deal on how to best accelerate their tissue recovery. Icing/heating the muscles to reduce swelling and increase blood flow, along with plenty of rest, and rehabilitative low-intensity exercising, stretching, and massage thereapy, along with plenty of sleep and nutrition (such as water and creatine), are instrumental in this.

Nutrition and longevity

Calorie restriction

Lifespan may be somehow related to the amount of food energy consumedTemplate:Ref. 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 persists 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 tissueTemplate:Ref.

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 depositsTemplate:Ref. 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 FDA and Brunswick labs.

The French paradox

Template:Main It has been discovered that people living in the south live longer. Even though they consume a comparable amount of saturated fats, the rate of heart disease is lower in Southern France. Scientists believe that this could be a result of the regular consumption of low amounts of red wine on a daily basis. It is also possible that this could be the result of smaller consumption of processed carbohydrate and other junk foods.

On the other hand, living in the South requires the body to produce less heat, allowing a slower, and therefore healthier, metabolic rate.

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 that can help 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 1800's 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.

Advice and guidance on nutrition

Governmental policies

Most Governments provide guidance on good nutrition, and some also impose mandatory labelling requirements upon processed food manufacturers to assist consumers in complying with such guidance. Current dietary guidelines in the United States are presented in the concept of a food pyramid. There is no apparent consistency in science-based nutritional recommendations between countries, indicating the role of politics as well as cultural bias in research emphasis and interpretation.

Teaching

Nutrition is taught in schools in many countries. In England and Wales the Personal and Social Education and Food Technology curriculums include nutrition, stressing the importance of a balanced diet and teaching how to read nutrition labels on packaging.

Issues

Challenging issues in modern nutrition include:

'Artificial' interventions in food production and supply:

Sociological issues:

  • Is it possible to eat right 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?
  • 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?
  • 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

For detailed information, see related entries in the following categories:


Profession:


Food:


Health:


Research:

References

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  2. Template:Note"Can a virus make you fat?" at BBC News; "Contagious obesity? Identifying the human adenoviruses that may make us fat" at Science Blog
  3. Template:NoteShils et al. (2005) Modern Nutrition in Health and Disease, Lippincott Williams and Wilkins. ISBN 0781741335.
  4. Template:Note Seddon JM et al. JAMA. 1994; 272: 1413-1420; Schepens Eye Institute/Harvard Medical School, Nov. 11, 2003. See http://www.mdsupport.org/library/zeaxanthin.html.
  5. Template:Note Lyle, B. J., J. A. Mares-Perlman, et al. (1999). "Antioxidant intake and risk of incident age-related nuclear cataracts in the Beaver Dam Eye Study." Am J Epidemiol 149(9): 801-9; Yeum, K. J., A. Taylor, et al. (1995). "Measurement of carotenoids, retinoids, and tocopherols in human lenses." Invest Ophthalmol Vis Sci 36(13): 2756-61; Chasan-Taber, L., W. C. Willett, et al. (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; Brown, L., E. B. Rimm, et al. (1999). "A prospective study of carotenoid intake and risk of cataract extraction in US men." Am J Clin Nutr 70(4): 517-24.
  6. Template:Note Am J Clin Nutr, Vol. 82, No. 2, 451-455, August, 2005 (inflammatory polyarthritis); Am J Epidemiology 2006 163(1).
  7. Template:NoteAm J Clin Nutr, Vol. 70, No. 2, 247-251, August 1999.
  8. Template:NoteWeindruch R, et al. The retardation of aging in mice by dietary restriction: longevity, cancer, immunity and lifetime energy intake. Journal of Nutrition, 116(4), pages 641-54.,April, 1986.
  9. Template:NoteBluher, Khan BP, Kahn CR, Extended longevity in mice lacking the insulin receptor in adipose tissue. Science 299(5606): 572-4, Jan 24, 2003.
  10. Template:NoteDas M, Gabriely I, Barzilai N.Caloric restriction, body fat and aging in experimental models. Obes. Rev. 2004 Feb;5(1):13-9.
  • 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.
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  • 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

Nutrition databases

Personalised services

Other

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