Nutrition is interpreted as the study of the organic process by which an organism assimilates and uses food and liquids for normal functioning, growth and maintenance and to maintain the balance between health and disease. Also included is the idea of an optimal balance of nutrients and whole foods, to enable the optimal performance of the body.
As recently as the 1960s doctors told their patients that nutrition had little to do with their health. Now we know otherwise: "you are what you eat!" More specifically, in humans, the matter which comprises the cells of the body (except those cells produced before birth) is acquired from food in the digestive system. Not all the food matter in the stomach can be used for the body; the matter that is left over as waste is removed.
Study in this field must take into account the state of the animal before ingestion and after digestion as well as the chemical content of the food and the waste. The specific types of matter (chemicals) that are absorbed by the body can be determined by comparing the waste to the food. 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 active variables involved in this type of experimentation is very high. This makes scientifically valid nutritional study very time consuming which accounts for why a proper science of human nutrition is rather new.
History and recent developments
This new science has rapidly expanded. Vitamins were first written about in 1912, by Sir Frederick Gowland Hopkins, who was knighted and received the Nobel Prize in 1929 for his achievements.
In the 20th century, after clarification of the nature and role of proteins, carbohydrates, vitamins and minerals, it was thought that we had adequate knowledge about the elements of food. Food was seen as the fuel, and we simply had to have enough of its ingredients in order to go on living. However, there followed an accelerating series of discoveries starting with fibre, which has revealed increasingly large gaps in our knowledge about the role of food in our health and proper functioning.
We now know that there are many thousands of phytochemicals in our food, each of them performing an essential role in the proper functioning of our bodies. Furthermore, it is thought that there are many more phytochemicals and other components of food to be discovered. There are also enzymes which play an important part in nutrition: these are chemical catalysts in our food and also produced in our digestive system. They are vitally important in all the metabolic activity in our bodies.
Antioxidants are another recent discovery. Using energy in our bodies often has damaging side effects on cells, and certain food elements such as vitamin C have been seen to be vital in protecting against the aging effect of this oxidizing damage. Recently the health benefits of vitamin E have been called into question.
The balance of essential fatty acids (linoleic and linolenic oil) has been discovered to be crucial in maintaining good health. This involves omega 3 and omega 6 oils, as well as the need to minimise hydrogenated fats which contain heavy metals.
Results are emerging to indicate that phytoestrogens in our food are related to the avoidance of metabolic syndrome, the regulation of cholestorol, and maintenance of bone density. (See medical abstract (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15303407&itool=iconabstr), and references Merrit, 2004, Mei 2001 below).
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 previous mechanistic view of food as fuel, and the simplistic notion that protein, carbohydrate etc. were each obtained from one type of food (the meat and two veg model) has all but been replaced. Increasing complexity means that nutrition researchers today advocate a holistic approach. They readily admit that there are many nutrients and other factors we don't know enough about, and that most foods contain most types of nutrients in various proportion. Provided excess is avoided, particularly of carbohydrates and hydrogenated fats, then it has been shown that our needs are best met through eating a wide variety of fresh, unprocessed and unmanufactured food.
The Institute for Food Additives and Ingredients gives the following information:
- "Far more is now known about the science of nutrition than ever before and the overriding message is that a very broad diet, taking in vital categories of essential nutrients, is better than a narrowly focussed diet, even if that diet sets out to avoid dangerous foodstuffs such as saturated fats.
- A survey has shown that the Japanese tend to eat a greater variety of different foods every day than Westerners (27 different foods a day whereas the recommended minimum in the West is 30 different foods per week); they are less prone to the 'diseases of civilization' - diabetes, heart disease and cancer - than Europeans, and their varied diet is thought to contribute to this."
People in Japan eat far more salt than people in the west.
Nutrition and health
In the 18th Century, many sailors on long journeys died from scurvy; indeed, some naval ships lost more men through illness than through enemy action. The cause of this was not understood, until it was discovered that adding fresh limes to the ship’s supply of preserved food seemed to boost the sailor’s resistance to the illness, and fewer died. The existence of parts of food essential for survival had been discovered. Other so-called vitamins were discovered through the effect of their absence on people’s health, and increasingly the role of nutrition’s contribution to health was seen as equally important as exercise, hygiene, environment, and psychological wellbeing.
The connection between nutrition and health has weakened however. Good health became the norm in the developed world through increased understanding of communicable diseases, micro-organisms and how to fight them with antibiotics, and other health developments. A hidden epidemic gradually emerged in the post World War II years, where non-communicable endemic illnesses began to flourish, such as heart disease, cancer, diabetes and obesity.
These illnesses are increasingly recognised now as being sometimes caused by lifestyle issues, including poor nutrition and low levels of exercise. Despite this knowledge, the peak of the epidemic is still with us, and obesity-related diseases are prevalent in the developed world.
Many nutritionists ascribe this to excess of refined carbohydrates, decreasing levels of exercise, fewer vegetables and fruit and the wrong types of fat in our diet. Others feel that governments and the food industry have not yet recognised or acted upon this insight. Fast food restaurants are spreading around the world, and Westernisation has unfortunately brought the "diseases of civilisation" with it. A reaction to this has been the development of a slow food trend. This has now got its own University, at the University of Pollenzo in Piedmont Italy whose goal is to promote awareness of good food and health through nutrition.
Nutrition research has identified many components of good nutrition, so that in general a wide variety of unprocessed food is recommended as a natural preventive measure, to maintain good health rather than individual foods as remedies for perceived deficiencies.
Nutrition can affect health in many ways. Ill-health can be brought about by an imbalance of nutrients, producing either an excess or deficiency which in turn affects body functioning in a cumulative manner. The body can be affected at the micro or macro levels by nutrition, for example cancer can arise through cell metabolism malfunction, and high energy levels can promote health through frequent activity.
Some examples are :
- Obesity results in fatty deposits in the abdomen which in turn affect the efficiency of the liver, heart, gall bladder, circulation etcetera. (See Janssen I, et al,. 2004)
- The wrong kinds of fats can cause the build-up of cholesterol-related plaque on artery walls which can eventually result in a blockage or poor blood supply to other organs, e.g. the brain or the heart itself, indirectly therefore causing angina, heart failure, brain disfunctioning, CVAs etc..
- An excess of carbohydrates, especially sugars, can lead to imbalances in insulin production. This in turn can lead to fatigue, chronic tiredness, diabetes, and obesity through overeating.
- Mineral or vitamin deficiencies are thought to be responsible for many illnesses, including goitre, scurvy, osteoporosis, poor immune system response (and indirectly some forms of cancers), disorders of cell metabolism, premature aging etc., poor psychological health, including eating disorders.
- Imbalances in omega 3 and omega 6 fatty acids is thought to be related to autism and some attention disorders  (http://www.faia.org.uk/roleofnutrition.php), and bipolar disorder (See Sobczak S, et al 2994, and the Times newspaper February 28, 2004 Autism: I can see clearly now . . . by Simon Crompton).
- Intolerance of gluten (a protein in wheat and rye) is suspected of being related to the development of schizophrenia in some cases. (See British Medical Journal, February 21, 2004.)
- Alzheimer's disease may be linked to B vitamin deficiencies. (See the Times newspaper, January 31 2004 "Could vitamins help delay the onset of Alzheimer’s?" by Jerome Burne).
Food can be made safer and more palatable through processing. Food processing therefore has a valuable role in contributing to good nutrition. However, some nutritionists advise caution.
Food processing is sometimes seen as adversely affecting people’s health: polished rice was identified as a cause of beri-beri when people realized that removing the skin of the rice was a process which removed essential nutrients.
In the late 1800s in the United States, babies started developing scurvy; there was a veritable plague. 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, causing a nutritional disease.
Other examples of adverse effects of food processing, together with research findings and the need to be cautious in the light of our limited and incomplete knowledge, have called food processing into question.
Today's leading nutritionists advise against the processing of food where possible, since undiscovered but possibly essential nutrients may be thereby removed, or toxins may be added or produced through processing and high temperature cooking. Also processing can replace some of the mechanical/biochemical body processes which are essential for full digestion, and hence good nutrition.
Cornell nutritional biochemist T. Colin Campbell, Professor and director of the China project stated at a symposium on epidemiology:
- "Analyses of data from the China studies ... is leading to policy recommendations." He mentioned three:
- "The greater the variety of plant-based foods in the diet, the greater the benefit. Variety insures broader coverage of known and unknown nutrient needs.
- Provided there is plant food variety, quality and quantity, a healthful and nutritionally complete diet can be attained without animal-based food.
- The closer the food is to its native state -- with minimal heating, salting and processing -- the greater will be the benefit."(Cornell Chronicle 28/6/01) (http://www.news.cornell.edu/Chronicle/01/6.28.01/China_Study_II.html)
Nutrition and longevity
Lifespan is somehow related to the amount of food energy consumed: this was first systematically investigated in the seminal study by Weidruch et al (1986).
A simplistic pursuit of this principle of caloric restriction followed, involving research into longevity of those who simply reduced their food energy intake. Perhaps not surpisingly, people found that cutting down on food reduced their quality of life so considerably as to negate any possible advantages of lengthening their lives.
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 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. (Bluher et al, 2003)
In effect, it is now thought that the agent which increases longevity is leanness in animals, and that it is the accumulation of fatty tissue over the years which may gradually and inevitably reduce life expectancy.
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. (Das et al, 2004)
Lifestyle and nutritional needs
Adequate nutrition contributes to three outcomes which are necessary for the organism’s normal functioning.
- Adequate energy levels
- Maintaining proper body structures and processes, e.g. muscle function, immune protection, bone density and strength
- Repair and development of all of the organism’s systems.
In the case of humans, ‘normal functioning’ is affected by a range of situations, which are often open to choice. A weightlifter, labourer, Inuit fisherman, Sumo wrestler, clerical worker, infant and bed-bound person will all have different definitions of ‘normal functioning’, they all have different body shapes and sizes, and their nutritional needs will vary also.
Consequently, suitable nutrition varies according to each individual’s situation, and to some extent on the choice of lifestyle. Athletes may need high levels of protein and energy to enable high performance and repair for the high stresses on their body. People working hard in a cold environment may need high fat levels in their diets, to help maintain normal body temperature. This beneficial high fat level may be very harmful for people in other situations, eg a sedentary worker in an air-conditioned office.
So the aim of good nutrition in terms of body maintenance, repair and functioning will be often relative to the choices and circumstances of the individual.
However, the holistic model of nutrition points out that for example high energy needs can be met in various ways, some more healthful than others. Food energy can be obtained from most foods, and are probably best obtained from those foods which have as high a concentration of other nutrients as possible.
Thus although nutrition and food types vary widely according to lifestyles and situations, nevertheless within each different set of requirements the principles of good nutrition can still be applied.
SeeNicholas Institute for Sports Medicine and Trauma (http://www.nismat.org/nutricor/healthydiet.html) for nutrition advice for sports people.
Policy advice and guidance on nutrition
Most Governments provide guidance on good nutrition. Current dietary guidelines in the United States are presented in the concept of a food pyramid. The pyramid has been criticised as outdated and fundamentally flawed allegedly because it serves the interests of the food industry. (See Wall Street Journal reference (http://www.karlloren.com/diet/p109.htm)). Detailed information on general nutrition is available from the Department of Agriculture's Food and Nutrition Information Center (http://www.nal.usda.gov/fnic/).
Nutrition is a fast-changing science, yet agriculture, food distribution, food manufacturing and Government policy are slow-changing things. Because of these facts, there is a recognition that official Government guidance may not be the best advice to follow: more fluid and responsive channels for advice may be needed in the future. "Recommended daily allowances" and the "five portions" policies are increasingly looking like arbitrary figures, as our knowledge increases.
Cornell nutritional biochemist T. Colin Campbell, Professor and director of the China project states:
- "...merely eating some low-fat foods or complying with current U.S. dietary recommendations is unlikely to prevent much disease... To get really significant changes in disease rates, it will be necessary to shift the American diet from its heavy reliance on animal-based foods to one that relies far more on plant-based foods" (Cornell Chronicle 10/1/94)
(See also: Walter C. Willett and Meir J. Stampfer,Rebuilding the Food Pyramid, Scientific American January 2003.)
A holistic approach
There are many more nutrients than we know about in food, and the overall process of ingestion and utilisation of nutrients is still poorly understood. Good nutrition is also part of, and depends on, such matters as healthy lifestyle, food policy, and public health. Such figures as longevity do not necessarily correlate to the developed status of a country. (For instance, Costa Rica and Guadaloupe have higher life expectancy than the United States, U.N figures 2002).
Because of these limitations, nutritionists are moving towards providing more holistic advice: they recommend increased exercise, a wider range of foods, using less food processing and cooking, increased vegetable and fruits, and less animal-based foods.
If these wider areas of advice are followed, then specific traditional nutritional intervention may only be needed for individual situations of illness or deficiency.
Examples are the comments by T. Colin Campbell on policy recommendations (see quotes above, in 'Nutrtion and health'), and the advice of Professor Thomas Sanders, the director of the Nutrition, Food & Health Research Centre at King’s College London , who says:“In trials, there is no evidence suggesting that reducing fat intake has an effect on obesity. As long as your expenditure equals what you eat, you won't put on weight, regardless of how high the fat content is in your diet.” (Times newspaper, 10 March 2004 or 3 October 2004, whatever those silly all-digit dates 10/3/04 meant)
Current issues and controversies
Controversies in modern nutrition include:
'Artificial' interventions in food production and supply:
- 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 ?
- How much meat and animal products are appropriate in diet (see also vegetarian and vegan)?
- 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?
- How large a place should dairy products take in the food pyramid?
- Does an increase in the plant content of our diet reduce the risk of developing some chronic illnesses? Conversely, is it true that increases in animal products in food increases the incidence of some diseases?
- What more can we discover through what has been called the phytochemical revolution?
- How essential to proper digestion are the enzymes contained in food itself, which are usually destroyed in cooking(see Living foods diet)?
To do: Edit this section further to remove anti-meat/pro-vegetarian bias and provide a more balanced view.
For detailed information, see related entries in the following categories:
- Bluher, Khan BP, Kahn CR, Extended longevity in mice lacking the insulin receptor in adipose tissue. Science 299(5606): 572-4, Jan 24, 2003.
- 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
- Das M, Gabriely I, Barzilai N.Caloric restriction, body fat and aging in experimental models. Obes Rev. 2004 Feb;5(1):13-9.
- William Eaton et al Coeliac disease and schizophrenia British Medical Journal, February 21, 2004.
- Janssen I, Katzmarzyk PT, Ross R. Waist circumference and not body mass index explains obesity-related health risk. Am J Clin Nutr. 2004 Mar;79(3):379-84.
- J Mei, SSC Yeung et al "High dietary phytoestrogen intake and bone mineral density in postmenopausal women."Journal of Clinical Endocrinology and Metabolism, 2001, Vol 86, Iss 11
- Merritt JC "Metabolic syndrome: soybean foods and serum lipids."J Natl Med Assoc. 2004 Aug;96(8):1032-41.
- Sobczak S, et al 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,Rebuilding the Food Pyramid, Scientific American January 2003.
- Weindruch 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.)
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