Nutrition is the combination of elements consumed by a person that nourishes the body, enabling it to sustain in an efficient manner all of its functions. Nutritionists seek to further understand by objective scientific method the nutritional needs of people to attain health and avoid disease and artfully try to work with people's varied lifestyles, cultural heritages, and tastes to enable those needs to be met through enjoyable eating patterns (Noakes and Clifton 2006).
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.
Although many organisms can survive on a limited variety of food sources, human nutrition is aided through the relationship with a vast array of plants and animals. To gain all the amino acids, fatty acids, carbohydrates, vitamins, and other nutriments necessary for good health, it is recommended that humans have a varied diet, which may include fish, seaweed, whole grains and legumes, nuts and seeds, vegetables and fruits, and so forth. Even microorganisms play a role in human nutrition, as a symbiotic relationship with bacteria in the gut aids digestion.
Internal aspects are also important, as digestion is aided by a good mood and hindered when under stress.
Nutrition relates to individual and social responsibility. On the one hand, personal discipline is required to have a good diet. On the other hand, people have a responsibility to care for society at large, such as aiding those without means for proper nutrition, overseeing the processing of foods that may be inexpensive but lack nutritional value, and investigating and educating on what constitutes a good dietary lifestyle.
The science of nutrition attempts to understand how and why specific dietary aspects influence health.
Nutritional knowledge is applied in four broad areas.
- Firstly, the general population, as world governments and individuals are concerned with the general health and productivity capacity of people.
- Secondly, people in emergencies—whether they be from natural disasters or conflict zones—supporting refugees to survive or those in hospitals who can not feed themselves.
- Thirdly, sections of the population that are challenging the boundaries of human limitation such as athletes and astronauts.
- Finally, the use of nutrients for those with limited dietary choices, to counter the impact of genes, allergies, or food intolerances to ensure these individuals still their nutritional needs fulfilled.
Nutrition is one of the most important physiological components for the body's good health, with fresh water, air, and exercise being other components. Of course, there are other contributing elements to a person's health, including psychological, spiritual, and social aspects.
Nutrition science seeks to explain metabolic and physiological responses of the body to diet. With advances in molecular biology, biochemistry, and genetics, nutrition science is additionally developing into the study of integrative metabolism, which seeks to connect diet and health through the lens of biochemical processes. Nutritionists are seeking to know which chemical components of food supply energy, regulate body processes, or promote the growth and repair of body tissue (Hey College of Somatic Studies 1998).
The RDA (recommended daily intake) relates to essential nutrients considered to be adequate to meet the nutritional needs of healthy people with moderate levels of activity. Although all persons have the need for the same nutrients, the amounts of the nutrients required by an individual are influenced by age, sex, body size, environment, level of activity, and nutritional status. The nutritional status of a person can be assessed by evaluation of dietary intake, anthropometric measurement, health assessment and laboratory tests (Pleuss 1998).
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 or may not contain minerals such as calcium, iron, or 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. All of the essential elements must be present, and for some with certain genetic conditions where they lack a certain enzyme such that other nutrients are not manufactured by the body, these must be supplied in the diet as well. Adequate and properly proportioned nutrition gives a person more options in life, enabling them to have the resources they need to fulfill their daily activities.
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; 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 3 to 4 hours) has also proven more hormonally and metabolically favorable than infrequent, haphazard food intake (WHO 2005).
Nutrition and health
It is important to consume these six nutrients on a daily basis to build and maintain healthy body systems. What the body is able to absorb through the small intestine into the blood stream—and from there into individual cells—is influenced by many factors, especially the efficiency of the digestive system, which is why two people of similar build may eat the same food but will have different nutritional outcomes.
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 signaling (e.g. as building blocks or part of hormone or signaling "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
Protein is the major functional and structural component of all the cells in the body. It is needed, for example, to form hormones, enzymes, antibodies for the immune system, blood transport molecules, and nucleic acids, as well as build the muscles, blood and its vessels, skin, hair, liver, and brain. If there are insufficient carbohydrates or oils in the diet, protein can be used as an inefficient form of heat and energy (Garrow and James 1996; Kirschmann 1979).
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. 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.
Protein is provided in the diet by eating flesh foods (fish, eggs, chickens, and meat) and the combining of lentils or other legumes with brown rice, millet, or buckwheat; or legumes with nuts or seeds (hence the value of hommus as a economical effective protein source for many parts of the world). Inadequate protein in the diet can lead to kwashiorkor. If calories and protein are inadequate, protein-calorie malnutrition occurs.
Although most fatty acids can be manufacture by the body from dietary oils, carbohydrates and proteins, there are two essential fatty acids that need to be consumed. These two are linoleic acid and linolenic acid.
The RDA ("recommended daily allowance," or "recommended daily intake," RDI) for the essential fatty acids (EFA) is one to two percent of total energy intake. Persons at risk for EFA deficiency tend to be the same as those at risk for fat soluble vitamin deficiencies, especially vitamin E. Some signs are shared by the deficiencies. The most specific sign for linoleic acid deficiency is eczematous dermatitis. Premature infants, infants from poorly nourished mothers, and those suffering fat malabsorption syndromes tend to become deficient (Brody 1999). As well, those who have the EFAs in the trans form rather than the cis would experience this. The body can only use the trans form as fuels and not as part of the essential functions, noted below (Lucy 1990).
The essential fatty acids are the starting point for the manufacture of prostaglandins, leukotrienes, prostcyclins, and thromboxanes. They alter the removal of low density lipoproteins and promote reduction of cholesterol. EPAs also are part of the structure of phospholipids in all cell membranes. Furthermore, EPAs are needed for neural function in the brain and eyes, and are needed for the synthesis of myelin.
Linolenic acid belongs to the family of omega-3 fatty acids (polyunsaturated fatty acids with a carbon-carbon double bond in the ω-3 position) and linoleic acid belongs to the family of omega-6 fatty acids (the first double bond in the carbon backbone occurs in the omega minus 6 position). In addition to sufficient intake of the essential fatty acids, an appropriate balance of 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 that 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 industrialized 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).
Glucose, the currency of energy for the body, is available from some fruit and vegetables directly, but also through the digestion and processing of other carbohydrates, fats, and proteins. The deficiency and excess consumption of sufficient energy components has serious repercussions for health.
Several lines of evidence indicate lifestyle-induced hyperinsulinemia (excess levels of circulating insulin in blood) 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 fueled 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 signaling 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).
Vitamins and minerals
Mineral and/or vitamin deficiency or excess may yield symptoms of diminishing health such as goiter, 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 (Shils et al. 2005).
As of 2005, 12 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).
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 antioxidants are produced by the body with adequate precursors (glutathione, vitamin C). Those that the body cannot produce may only be obtained through the diet through direct sources (vitamins A, C, and 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).
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 (Rice 1996).
Intestinal bacterial flora
It is now known that the human digestion system contains a population of a range of bacteria and yeast, such as bacteroides, L. acidophilus and E. coli, that 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 (Brody 1999).
A growing area of interest is the effect upon human health of trace chemicals, collectively called phytochemicals, nutrients typically found in edible plants, especially colorful fruits and vegetables. 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) (Seddon et al. 1994). Less rigorous studies have proposed a correlation between zeaxanthin intake and cataracts (Lyle et al. 1999). 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 (Pattison et al. 2005) 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. 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 (Handelman 1999). As another example, lycopene is prevalent in tomatoes (and actually is the chemical that gives tomatoes their red color). It is more highly concentrated, however, in processed tomato products such as commercial pasta sauce, or tomato soup, than in fresh "healthy" tomatoes. Such sauces, however, tend to have high amounts of salt, sugar, other substances a person may wish or even need to avoid. The more we prepare food ourselves from fresh ingredients, the more knowledge and control we have about the undesirable additives.
Nutrition and sports
Nutrition is very important for improving sports performance. Athletes need only slightly more protein than an average person, though strength-training athletes need more (Sports Nutrition Society 2006). Consuming a wide variety of protein sources, including plant-based sources, helps keep an overall health balance for the athlete (Nismat 2006).
Endurance, strength, and sprint athletes have different needs. Many athletes may require an increased caloric intake. Maintaining hydration during periods of physical exertion is an important element to good performance. While drinking too much water during activities can lead to physical discomfort, dehydration hinders an athlete’s ability (Nismat 2007).
Nutrition and longevity
Lifespan prolongation has been researched related to the amount of food energy consumed. Underlying this research was the hypothesis that oxidative damage was the agent that accelerated aging, and that aging was retarded when the amount of carbohydrates (and thereby insulin release) was reduced through dietary restriction (Weindruch et al. 1986). 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.
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 (Bluher et al. 2003).
This has set researchers off on a line of study that presumes that it is not low food energy consumption that 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 (Das et al. 2004). 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 contributes.
Antioxidants have recently come to the forefront of longevity studies.
Healthy diet and whole plant food diet
Walter Willett, author of Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating made the following observation (Willett 2004):
The potential impact of healthy diet, when you combine it with not smoking and regular physical activity, is enormous. For example, our studies have shown that we could prevent about 82 percent of heart attacks, about 70 percent of strokes, over 90 percent of type 2 diabetes, and over 70 percent of colon cancer, with the right dietary choices as part of a healthy lifestyle. The best drugs can reduce heart attacks by about 20 or 30 percent, yet we put almost all of our resources into promoting drugs rather than healthy lifestyle and nutrition.
Cross-cultural international studies have shown that it is lifestyle choices, ways of cooking and eating, as well as specific nutritional components, that lead to increased heart disease (Willett 2004).
The autonomic nervous system, which controls the allocation of resources in the body depending on the priority for the body's survival, influences powerfully the effectiveness of the action of the digestive tract, including the digestion, absorption of nutrients, and the expulsion of waste products (Porth 1998). When a person eats in a relaxed jovial state, the body can allocate its full ration of resources to this process through the parasympathetic nervous system branch dominating. Therefore, the person gains more nutrients from the food and fewer nutrients are wasted by the quick expulsion of waste. If, however, we are feeling stressed, and gulp our food down as quickly as possible, the sympathetic branch will dominate and in extreme cases hardly any resources are allocated to the digestive process. Not only do we receive less nutritional benefit from the food, we are more likely to be constipated or have longer expulsion time of waste, which uses more nutrients to neutralize their longer stay in the body.
Following the history of the discovery of the different vitamins and phytochemicals, it is prudent to be eating a wide variety of foods from a variety of sources, if available. That is, some food from the water (fish, seaweed, and algae), a wide variety of whole grains and legumes (rice, millet, buck wheat, corn, wheat, lentils, peas, and beans), nuts and seeds, many types of vegetables, fresh cooked herbs and greens, and a variety of fruits and flesh foods. Scientists will always be discovering new and exciting chemicals in the different foods and trying to reproduce their chemical structure synthetically for specific purposes, but there will never be a magic formula of synthetic food that will do away with the many reasons that the body is designed to take in elements in a form available in the food around it and to then transform it into the multitude of sub-chemicals it manufactures.
Heart disease and cancer are commonly called "Western" diseases because of a widespread belief that these maladies are rarely seen in developing countries. In fact, "more 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. It does highlight the impact of smoking, obesity, lack of exercise, diet, and age for the still 18 percent higher rate of cancer in wealthier countries in men.
Research in China finds the difference may be nutritional: the Western diet includes consumption of large quantities of animal foods that 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” (Campbell 2005). 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." In common with all three groups is to "Eat fruits, vegetables, and whole grains." As the results from the phytochemicals show there are many elements in food and the way it is prepared that have an impact on the consumer’s nutritional status. The maxim eat a wide variety of natural foods in moderate quantities slowly chewing well in a relaxed setting has stood the test of time and scientific scrutiny.
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."
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, but many more technologies have been invented to allow foods to last longer without becoming spoiled. These latter technologies include pasteurization, autoclavation (sterilization using pressure to heat solutions above their boiling point), drying, salting, and separation of various components; all appear to alter the original nutritional contents of food. Pasteurization 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 concentration of particular components of food, yielding flour, oils, juices and so on, and even separate fatty acids, amino acids, vitamins, and minerals. Inevitably, such large scale concentration changes the nutritional content of food, saving certain nutrients while removing others. Heating techniques may also reduce food's content of many heat-labile nutrients, such as certain vitamins and phytochemicals, and possibly other yet to be discovered substances (Morris et al. 2004).
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, particularly as regards content of both sugar and high GI starches, potassium/sodium, vitamins, fiber, and 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 beriberi in people subsisting on polished rice. Removing the outer layer of rice by polishing it also removes the essential vitamin thiamine, causing beriberi. Another example is the development of scurvy among infants in the late 1800s in the United States. It turned out that the vast majority of sufferers were being fed milk that had been heat-treated (as suggested by Pasteur) to control bacterial disease. Pasteurization 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 the modern economy, and as such it is influential in political decisions (e.g. nutritional recommendations, agricultural subsidizing). 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 (Greenfacts 2007).
Advice and guidance on nutrition
Most governments provide guidance on good nutrition, and some also impose mandatory labeling 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 some apparent inconsistency in science-based nutritional recommendations between countries, indicating the role of politics as well as cultural bias in research emphasis and interpretation. The over-representation of dairy foods in the United States food pyramid may be an example (Willett 2004).
Nutrition is taught in schools in many countries. In England and Wales, for example, 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.
Antiquity through Enlightenment
- c. 475 B.C.E.: Anaxagoras states that food is absorbed by the human body and therefore contained "homeomerics" (generative components), thereby deducing the existence of nutrients.
- c. 400 B.C.E.: 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 ten 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 Royal 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 by scientists until the 1930s.
- 1770: Antoine Lavoisier, the "father of nutrition and chemistry," discovered the details of metabolism, demonstrating that the oxidation of food is the source of body heat.
- 1790: George Fordyce recognized calcium is necessary for fowl survival.
Modern era (through 1941)
- Early 1800s: The elements carbon, nitrogen, hydrogen, and oxygen were recognized as the primary components of food, and methods to measure their proportions were developed.
- 1816: François Magendie discovers that dogs fed only carbohydrates and fat lost their body protein and died in a few weeks, but dogs also fed protein survived, identifying protein as an essential dietary component.
- 1840: Justus Liebig discovers the chemical makeup of carbohydrates (sugars), fats (fatty acids), and proteins (amino acids.)
- 1860s: Claus Bernard discovers that body fat can be synthesized from carbohydrate and protein, showing that the energy in blood glucose can be stored as fat or as glycogen.
- Early 1880s: Kanehiro Takaki observed that Japanese sailors developed beriberi (or endemic neuritis, a disease causing heart problems and paralysis) but British sailors did not. Adding milk and meat to Japanese diets prevented the disease.
- 1896: Baumann observed iodine in thyroid glands.
- 1897: Christiaan Eijkman worked with natives of Java, who also suffered from beriberi. Eijkman observed that chickens fed the native diet of white rice developed the symptoms of beriberi, but remained healthy when fed unprocessed brown rice with the outer bran intact. Eijkman cured the natives by feeding them brown rice, discovering that food can cure disease. Over two decades later, nutritionists learned that the outer rice bran contains vitamin B1, also known as thiamine.
- 1890: The British government is shocked to realize it was nearly defeated in the Boer War because of the poor health of its population, due to insufficient and improper food in the homes of the poor, and so a school meal program was started.
- Early 1900s: Carl Von Voit and Max Rubner independently measure caloric energy expenditure in different species of animals, applying principles of physics in nutrition.
- 1906: Wilcock and Hopkins showed that the amino acid tryptophan was necessary for the survival of mice. Gowland Hopkins recognized "accessory food factors" other than calories, protein, and minerals, as organic materials essential to health, but which the body cannot synthesize.
- 1907: Stephen M. Babcock and Edwin B. Hart begin the single-grain experiment. This experiment runs through 1911.
- 1912: Casimir Funk coined the term vitamin, a vital factor in the diet, from the words "vital" and "amine," because these unknown substances, preventing scurvy, beriberi, and pellagra, were thought then to be derived from ammonia.
- 1913: Elmer 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.
- 1922: McCollum destroys the vitamin A in cod liver oil but finds it still cures rickets, naming it 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 that the body cannot synthesize.
- 1935: Underwood and Marston independently discover the necessity of cobalt.
- 1936: Eugene Floyd Dubois shows that work and school performance are related to caloric intake.
- 1938: The chemical structure of vitamin E is discovered by Erhard Fernholz, and it is synthesised by Paul Karrer.
- 1941: The first Recommended Dietary Allowances (RDAs) were established by the United States National Research Council.
(Garrow and James 1996, Conlan and Sherman 2003)
- 1955: The development of the electron microscope and other scientific equipment allowed the metabolism and nutritional needs of individual cells and its components to be studied. As more biochemical information was discovered, the contrast between the knowledge of what cells needed and what people ate actually consuming, especially in affluent countries, became more alarming.
- 1987: The American surgeon general's report on nutrition and health asserted that at least half of all deaths in the United States were related to faulty diet, noting, "the convergence of similar dietary recommendations that apply to prevention of multiple chronic disease. Five of the ten leading causes of death in the USA are clearly related to wrong food choices. Diseases of nutritional deficiencies have declined and have been replaced by diseases of dietary excesses and imbalances—problems that now lead rank among the leading causes of illness and death, touch the lives of most Americans and generate substantial health care costs."
- 1992: The U.S. Department of Agriculture introduces the “Food Guide Pyramid.”
- 2002: Natural Justice Study shows a relation between nutrition and violent behavior.
- 2005: World Health Organization statement on diet: "For diet, recommendations for populations and individuals should include the following: achieve energy balance and a healthy weight; limit energy intake from total fats and shift fat consumption away from saturated fats to unsaturated fats and towards the elimination of trans-fatty acids; increase consumption of fruits and vegetables, and legumes, whole grains and nuts; limit the intake of free sugars; limit salt (sodium) consumption from all sources and ensure that salt is iodized. These recommendations need to be considered when preparing national policies and dietary guidelines, taking into account the local situation. Improving dietary habits is a societal, not just an individual problem. Therefore demands a population-based, multisectoral, multi-disciplinary, and culturally relevant approach.”
- 2006: A study is conducted on the effect of gut bacteria on obesity (Med News 2006).
Challenging issues in modern nutrition include:
"Artificial" interventions in food production and supply:
- Should genetic engineering be used in the production of food crops and animals?
- Are the use of pesticides and fertilizers damaging to the foods produced by use of these methods?
- Are the use of antibiotics and hormones in animal farming ethical and/or safe?
- Is it possible to eat correctly on a low income? Is proper nutrition economically skewed? How do we increase access to whole foods in impoverished neighborhoods?
- How do we minimize 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 minimizing import tariffs and export subsidies on food transfers?
- Are dairy foods overemphasized in the food pyramid?
- Should treated foods advertising be restricted in children's TV programs?
- How do different nutrients affect appetite and metabolism, and what are the molecular mechanisms?
- Can a whole plant food diet, replete with diversity and colors, be instituted and implemented to improve health and reduce medical costs?
- What yet to be discovered important roles do vitamins, minerals, and other nutrients play in metabolism and health?
- Are the current recommendations for intake of vitamins and minerals appropriate?
- How and why do different cell types respond differently to chronically elevated circulating levels of insulin, leptin, and other hormones?
- What does it take for insulin resistance to develop?
- What other molecular mechanisms may explain the link between nutrition and lifestyle-related diseases?
- What role does the intestinal bacterial flora play in digestion and health?
- How essential to proper digestion are the enzymes contained in food itself, which are usually destroyed in cooking?
- What more can we discover through what has been called the phytochemical revolution?
- ↑ Michael Coren, “Study: Cancer no longer rare in poorer countries,” CNN.com (March 10, 2005). Retrieved July 19, 2007.
- ↑ BenBella Books, Inc. The China Study. Retrieved July 19, 2007.
- Bluher Khan, B. P., and C. R. Kahn. 2003. “Extended longevity in mice lacking the insulin receptor in adipose tissue.” Science 299 (5606): 572-574.
- Brody, T. 1999. Nutritional Biochemistry, 2nd edition. San Diego: Academic Press. ISBN 0121348369
- 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): 517-524.
- Burne, J. 2004. “Could vitamins help delay the onset of Alzheimer’s?” The Times (January 31, 2004).
- Campbell, T. Colin and Thomas M. Campbell II. 2005. The China Study. Dallas, TX: BenBella Books.
- Conlan, R., and E. Sherman. 2003. Unraveling the Enigma of Vitamin D. United States National Academy of Sciences.
- 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): 509-516.
- Crompton, S. 2004. “Autism: I can see clearly now.” The Times (February 28, 2004).
- Das, M. I. Gabriely, and N. Barzilai. 2004. Caloric restriction, body fat and aging in experimental models. Obes. Rev. 5(1): 13-19.
- Eaton, W. et al. 2004. “Coeliac disease and schizophrenia.” British Medical Journal (February 21, 2004).
- Galdston, I. 1960. Human Nutrition: Historic and Scientific. New York: International Universities Press.
- Garrow, J. S, and W. P. T. James. 1996. Human Nutrition and Dietetics, 9th ed. Melbourne: Churchill Livingstone. Historical Perspective 1-11.
- Greenfacts. 2007. To what extent does diet play a role in chronic diseases?. Greenfacts.org. Retrieved July 19, 2007.
- Hey. 1998. An Overview of Nutrition Clinical Nutrition Study Guide, Chapter 1. College of Somatic Studies (Australia).
- Handelman, G. J., Z. D. Nightingale, A. H. Lichtenstein, E. J. Schaefer, and J. B. Blumberg. 1999. “Lutein and zeaxanthin concentrations in plasma after dietary supplementation with egg yolk.” Am. J. Clinical Nutrition 70: 247-251.
- Jaeger, A-C. 2004. “Work up an Amish appetite.” The Times (March 10, 2004).
- Janssen, I., P. T. Katzmarzyk, and R. Ross. 2004. “Waist circumference and not body mass index explains obesity-related health risk.” Am J Clin Nutr. 79(3): 379-384.
- Kirschmann, G. J., and J. D. Kirschmann (eds.). 1996. Nutrition Almanac, 4th ed. New York: McGraw-Hill.
- Lucy, R. 1990. “Essential fatty acids.” Nutritional Therapy. Sydney: The College of Somatic Studies 8: 1-9.
- 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): 801-809.
- Mahan, L. K., S. Escott-Stump, eds. 2000 Krause's Food, Nutrition, and Diet Therapy, 10th ed. Philadelphia: W.B. Saunders Harcourt Brace.
- McGrath, M. 2000. Can a virus make you fat?. BBC News (July 28, 2000). Retrieved July 19, 2007.
- Med Bews. 2006. “Relative abundance of common microbes living in the gut may contribute to obesity.” Mednews. Retrieved January 15, 2007.
- Mei, J., S. S. C. Yeung, et al. 2001. “High dietary phytoestrogen intake and bone mineral density in postmenopausal women.” Journal of Clinical Endocrinology and Metabolism 86 (11).
- Merritt, J. C. 2004. “Metabolic syndrome: soybean foods and serum lipids.” J Natl Med Assoc 96 (8): 1032-1041.
- Morris, A., A. Barnett, O.-J. Burrows. 2004. “Effect of processing on nutrient content of foods.” CAJANUS 37(3): 160-164.
- Natural Justice Study. 2002. “Trying to find out what causes antisocial and criminal behaviour.”
- Nismat. 2006. Guidelines for a healthy diet. Nismat.org. Retrieved July 19, 2007.
- Nismat. 2007. Fluid needs of athletes. Nismat.org. Retrieved July 19, 2007.
- Noakes and Clifton. 2006. Interview with Dr. Manny Noakes and Dr. Peter Clifton, authors of The CSIRO Total Wellbeing Diet Book 2. The Sydney Morning Herald (October 26, 2006).
- Pattison, D. J., D. P. M. Symmons, M. Lunt, A. Welch, S. A. Bingham, N. E. Day, and A. J. Silman. 2005. “Dietary ß-cryptoxanthin and inflammatory polyarthritis: Results from a population-based prospective study.” Am. J. Clinical Nutrition 82: 451-455.
- Pleuss, J. 1998. “Alterations in nutritional status.” In C. Porth, Pathophysiology: Concepts of Altered Health States, 5th ed. Philadelphia: Lippincott-Raven. pp. 1249-1250.
- Porth, C. 1998. “Integrated Body Function.” In C. Porth, Pathophysiology: Concepts of Altered Health States, 5th ed. Philadelphia: Lippincott-Raven. p. 1238.
- Rice University. 1996. “Antioxidants and free radicals.” Retrieved July 19, 2007.
- Seddon, J. M. U. A. Ajani, R. D. Sperduto, et al. 1994. Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration. Eye Disease Case-Control Study Group. Journal of the American Medical Association 272: 1413-1420.
- Shils, M. E., M. Shike, A. C. Ross, B. Caballero, and R. J. Cousins (eds.). 2005. Modern Nutrition in Health and Disease. Philadelphia: Lippincott Williams & Wilkins.
- Weindruch, R., et al. 1986. “The retardation of aging in mice by dietary restriction: longevity, cancer, immunity and lifetime energy intake.” Journal of Nutrition 116(4): 641-654.
- Simopoulos, A. P. 1996. “The role of fatty acids in gene expression: health implications.” Ann Nutr Metab. 40(6): 303-311.
- 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. 34(1): 103-112.
- World Health Organization (WHO). 2005. “Healthy diet statement.” World Health Organization. Retrieved July 19, 2007.
- Willett W. C., and M. J. Stampfer. 2003. “Rebuilding the food pyramid.” Scientific American (January 2003).
- Willett, W. 2004. PBS Frontline: Interview with Prof. Walter Willett, head of Harvard's nutrition department. PBS. Retrieved July 19, 2007.
- Yeum, K. J., A. Taylor, et al. 1995. “Measurement of carotenoids, retinoids, and tocopherols in human lenses.” Invest Ophthalmol Vis Sci 36(13): 2756-2761.
All links retrieved February 12, 2015.
- The American Dietetic Association
- The British Dietetic Association
- The Irish Nutrition and Dietetic Institute
- Dietitians of Canada
- The Singapore Nutrition and Dietetics Association
- Dietitians Association of Australia
- New Zealand Dietetic Association
- Nutrition Data
- International Confederation of Dietetic Associations
- American Society for Parenteral and Enteral Nutrition
- Society for Behavioral Nutrition and Physical Activity
- International Society of Sports Nutrition
- The Food and Nutrition Information Center
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