 UTRITION SCIENCE STUDIES the relationships between diet and states of health and disease. Dieticians are health professionals who are specialized in this area of expertise, highly trained to provide safe, evidence-based dietary advice and interventions. There is a spectrum ranging from malnutrition to optimal health, including many common symptoms and diseases that can often be prevented or alleviated with better nutrition. Deficiencies, excesses and 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 (lead, mercury, PCBs and dioxins, for example) 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. Overview Nutrition science seeks to explain metabolic and physiologic responses of the body to diet. With advances in molecular biology, biochemistry and genetics, nutrition science is additionally developing into the study of integrative metabolism, which seeks to connect 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 (sugars and fiber). These compounds, in turn, consist of elements such as carbon, hydrogen, oxygen, nitrogen and phosphorus, and they may or may not contain minerals such as calcium, iron or zinc. Minerals ubiquitously occur in the form of salts and electrolytes. All these chemical compounds and elements occur in various forms and combinations (like hormones and vitamins), both in our body and in the plants and animals we 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 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, and they also modulate the conformation and energetic state of the compounds and elements. However, many compounds and 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, and the intestines reabsorb most of it. Otherwise, the body would rapidly dehydrate, as seen in the devastating effects of persistent diarrhea.
In general, eating a variety of fresh, whole (unprocessed) plant foods has proven hormonally and metabolically favorable 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 favorable balance of essential and vital nutrients per unit of energy. This results in better management of cell growth, maintenance and mitosis (cell division) and better regulation of blood glucose and appetite. A generally more regular eating pattern such as eating small meals every three to four hours has also proven more hormonally and metabolically favorable than infrequent, haphazard food intake. (Such a regimen is typical among bodybuilders.) 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 (as building blocks or part of 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, or 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 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 unfavorably 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 fuell ed 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. Phytochemicals
Blackberries are a source of polyphenol antioxidantsA 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-percent reduction in AMD. The difficulties in demonstrating causative properties and in applying the findings to human diet, however, are similarly enormous. (Continued in right-hand column)
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(Continued from left-hand column) 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, or other substances a person may wish, or even need, to avoid. And recently scientists have discovered the key to the ability of spicy foods to kill cancer cells. They found capsaicin, an ingredient of jalapeno peppers, trig gers cancer cell death by attacking mitochondria -- the cells' energy-generating boiler rooms. The research raises the possibility that other cancer drugs could be developed to target mitochondria.
The Nottingham University study features in Biochemical and Biophysical Research Communications. The study showed that the family of molecules to which capsaicin belongs, the vanilloids, bind to proteins in the cancer cell mitochondria to trigger apoptosis, or cell death, without harming surrounding healthy cells. The implications are obvious. Nutrition and sports Nutrition is very important for improving sports performance. Contrary to popular belief, athletes need only slightly more protein than an average person. These needs are easily met by a balanced diet, and the recommended daily servings are generous enough to meet these needs. Additional protein intake is broken-down to be used as energy or stored as fat. Excess protein or grain consumption in the absence of alkalizing mineral intake (from fruits and vegetables) leads to chronic low grade acididosis in which calcium and glutamine are leached from bone and muscle respectively to keep the blood pH steady.
Endurance, strength and sprint athletes have different needs. Many athletes may require an increased caloric intake.
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 hinders an athlete’s ability. It is recommended that an athlete drink about 400-600mL 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 .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 exhuastion as well as speed recovery. Dosage is based on work performed, lean body mass, and environmental factors (heat)
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.
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 (discussed in previous paragraphs) 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 and cancer are commonly called "Western" diseases because of a widespread, if wholly mistaken, belief that these maladies are rarely seen in developing countries. According to CNN a study by the International Agency for Research on Cancer shows "[m]ore women in developing countries die of cancer than in the rich world," and the previous low rates of cancer in poor countries are attributed by scientists to shorter life spans.
Research in China finds the difference may be nutritional; the Western diet includes consumption of large quantities of animal foods which could promote these observed diseases of affluence. One study found that rural Chinese eat mostly whole plant-based foods and "Western" diseases are rare; they instead suffer "diseases of poverty" which can be prevented by basic sanitation, health habits, and medical care.
In China some areas have essentially no cancer or heart disease, while in other areas, they reflect up to a 100-fold increase. Coincidentally, diets in China range from entirely plant-based to heavily animal-based, depending on the location.
The United Healthcare/Pacificare nutrition guideline recommends a whole plant food diet, as does a cover article of the issue of National Geographic (November 2005), titled The Secrets of Living Longer. The latter 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."
The French paradox  It has been discovered that people living in France live longer, and it's not only because they avoid military conflict. 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 be harmed less by fats;
regular consumption of red wine; or
the geographic location of France requires the body to produce less heat, allowing a slower, and therefore healthier, metabolic rate.
It should be noted that the word 'paradox' is meaningful only for those who believe that saturated fats are 'unhealthy.' In fact, statistics contradict this article of faith, as there appears to be no correlation among European countries between the level of saturated fat consumption and the risk of developing heart disease. Likewise, the Harvard Nurses study showed no correlation between the consumption of saturated fats and the risk of heart disease. 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 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. - END -
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