Structure and Functions (Magill’s Medical Guide, Sixth Edition)
Nutrients are necessary for all aspects of living, including cellular metabolism, individual organ function, and multiple organ systems function. Breathing, moving, thinking, playing, and working all rely on the availability of nutrients. The study of nutrition has revolved around either healthy growth and development or nutrition in relation to the prevention and treatment of disease. Periods of noticeable growth, such as pregnancy, infancy, childhood, and adolescence, are particular areas of study in nutrition because nutrient needs change during these periods.
The amount of calories required to maintain a healthy weight during each stage of the life cycle depends upon the amount of energy expended. Higher caloric requirements are found when body mass is relatively large and energy output is relatively high, as seen in later adolescence and young adulthood. Because men generally have a larger body mass than women, they usually have a larger caloric requirement.
Macronutrients. Carbohydrates are an important source of energy. The recommended range of intake is 45 to 65 percent of the total caloric intake. Each gram of carbohydrate contributes 4 calories to the diet. Carbohydrates are found in starchy foods such as potatoes or corn, in vegetables and fruits, and in milk and yogurt. Carbohydrates are not found in meats or fats unless the food is a mixed dish, such as a hamburger casserole or a candy...
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
Most chronic diseases result as a complex interaction between genetics and environmental factors. Diet is an important environmental factor that is potentially modifiable, and it has received much attention in the prevention of chronic disease. Most chronic disease prevention or treatment includes a nutritional component. The most prevalent chronic diseases in the United States are cancer, cardiovascular disease, diabetes, obesity, and osteoporosis.
Cancer. Although overall rates are declining in the United States, cancer continues to be a major cause of mortality. In general, cancer involves three phases: initiation, promotion, and progression. During the initiation step, there is a genetic alteration that may remain quiescent or continue though the second step of promotion. During promotion, cellular proliferation is stimulated and the abnormal cells begin to grow without regulation. The third phase is progression, when the neoplastic cells become invasive and spread or metastasize to other parts of the body. Dietary components may be involved in the initiation and promotion of certain cancers as well as their inhibition. The dietary components that have been linked to the development of cancer include dietary fat, total calories, and alcohol, as well as salted, cured foods and molds that may grow in certain foods.
Antioxidants have been investigated as inhibitors of cancer. Fruits and vegetables are...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Although the science of nutrition began as a branch of biochemistry, early discoveries of the health properties of food date to the eighteenth century and the discovery that limes could prevent the painful bleeding disorder scurvy. Since then, the knowledge of nutrition has progressed beyond identifying deficiency diseases toward an understanding and appreciation of the complexity of nutrition in optimal health. In addition to further investigations into macronutrients, vitamins, and minerals, many bioactive substances in foods are being identified, such as bioflavinoids and probiotics. The interactions of these and more traditional nutrients are being investigated as potential modifiers of chronic disease and promoters of longevity.
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
American Diabetes Association. American Diabetes Association Complete Guide to Diabetes. 4th rev. ed. New York: Bantam Books, 2006. Provides a comprehensive guide to self-management of diabetes, including practical advice for living and how to interact with the health care team.
Duyff, Roberta Larson. American Dietetic Association Complete Food and Nutrition Guide. 3d ed. Hoboken, N.J.: John Wiley & Sons, 2007. Provides an overview of nutritional needs through the life cycle, including food choices for healthy diets, vitamins, minerals, and macronutrients, as well as suggestions for meal planning and shopping.
Lichtenstein, Alice H., et al. “Diet and Lifestyle Recommendations Revision 2006: A Scientific Statement from the American Heart Association Nutrition Committee.” Circulation 114, no. 1 (July 4, 2006): 82-96. Provides an overview of the dietary recommendations for cardiovascular health and summary of the rationale for these recommendations.
U.S. Department of Health and Human Services and U.S. Department of Agriculture. Dietary Guidelines for Americans 2005. 6th ed. Washington, D.C.: Government Printing Office, 2005. Provides guidelines for healthy eating as well as food sources of nutrients and dietary patterns to prevent hypertension.
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Nutrition (Encyclopedia of Medicine)
Good nutrition can help prevent disease and promote health. There are six categories of nutrients that the body needs to acquire from food: protein, carbohydrates, fat, fibers, vitamins and minerals, and water.
Protein supplies amino acids to build and maintain healthy body tissue. There are 20 amino acids considered essential because the body must have all of them in the right amounts to function properly. Twelve of these are manufactured in the body but the other eight amino acids must be provided by the diet. Foods from animal source such as milk or eggs often contain all these essential amino acids while a variety of plant products must be taken together to provide all these necessary protein components.
Fat supplies energy and transports nutrients. There are two families of fatty acids considered essential for the body: the omega-3 and omega-6 fatty acids. Essential fatty acids are required by the body to function normally. They can be obtained from canola oil, flaxseed oil, cold-water fish, or fish oil, all of which contain omega-3 fatty acids, and primrose or black currant seed oil, which contains omega-6 fatty acids. The American diet often contains excess of omega-6 fatty acids and insufficient amount of omega-3 fats....
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Nutrition (Encyclopedia of Science)
The term nutrition refers to the sum total of all the processes by which an organism takes in and makes use of the foods it needs to survive, grow, move, and develop. The word nutrition is also used to refer to the study of the substances an organism needs in order to survive. Those substances are known as nutrients.
Some organisms, such as plants, require nothing other than a supply of light, water, and simple chemicals in order to thrive. Such organisms are known as autotrophs, or self nourishers. Autotrophs build all the molecules they need and capture energy in the process. A few nonplant autotrophic organisms live in the deep oceans near hydrothermal vents (cracks in the ocean floor caused by volcanic activity). These organisms are able to build their own nutrients without using sunlight from sulfur compounds found around the vents.
While green plants get the energy they need directly from sunlight, animals must get the energy they need for life functions from plants.
The major classes of nutrients are carbohydrates, proteins, lipids (or fats), vitamins, and minerals. Animals also need other substances, such as water, fiber, and oxygen, in order to survive. But these substances are not usually regarded as nutrients.
Proteins. Proteins are large molecules built from different...
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Nutrition (Science Experiments)
Eat right to stay healthy
Energizing Foods: Which foods contain carbohydrates and fats?
Design Your Own Experiment
The foods you eat affect whether you pay attention in class, how much energy you have for sports, and even whether you feel happy or sad. In fact, your meals and snacks affect how every cell in your body works. How do we know? is the science of how the body uses nutrients to grow and function effectively. NutrientsA substance needed by an organism in order for it to survive, grow, and develop. are nourishing substances that the body needs. For example, the heart needs certain nutrients to help it pump blood. Our kidneys need nutrients to help rid our bodies of harmful wastes. Not surprisingly, deficiencies in certain nutrients can cause disease.
Hardly anyone gets anymore, but this disease was common a few centuries ago, especially among the first explorers and the crews on their ships. No one knew what caused scurvy. People with it felt weak. Their gums, noses, and mouths bled, and their muscles ached. When the ship of French explorer...
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Nutrition (Encyclopedia of Children's Health)
The process by which humans take in and use food in their bodies; also the study of diet as it relates to health.
Good nutrition in childhood lays the foundation for good health throughout a person's lifetime. With the proliferation of fast food restaurants, the number of junk food commercials on television, and the increased trend toward eating out, it is more difficult than ever for parents to ensure that their children maintain a nutritious diet. Across the last decades of the twentieth century, increasing affluence and the widespread availability of vitamin-enriched foods have shifted the focus of nutritional concerns in the United States from obtaining minimum requirements to cutting down on harmful elements in one's diet. Parents need to be as concerned about high levels of fat, cholesterol, sugar, and salt, as well as adequate intake of vitamins, minerals, and other nutrients.
The American Academy of Pediatrics, the National Academy of Sciences, the American Heart Association, and other health-care organizations agree that fat should not account for more than 30 percent of the calorie intake of children over the age of two, and saturated fat should account for under 10 percent. The main...
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Nutrition (Encyclopedia of Alternative Medicine)
Good nutrition can help prevent disease and promote health. There are six categories of nutrients that the body needs to acquire from food: protein, carbohydrates, fat, fibers, vitamins and minerals, and water.
Protein supplies amino acids to build and maintain healthy body tissue. There are 20 amino acids considered essential because the body must have all of them in the right amounts to function properly. Twelve of these are manufactured in the body but the other eight amino acids must be provided by the diet. Foods from animal sources
|FOODS HIGH IN SUGAR|
|Peanut butter and jelly sandwich|
|Pork and beans|
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Nutrition (Encyclopedia of Nursing & Allied Health)
Good nutrition can help prevent disease and promote health. There are six categories of nutrients that the body needs to acquire from food: protein, carbohydrates, fat, fibers, vitamins and minerals, and water.
Protein supplies amino acids to build and maintain healthy body tissue. There are 20 amino acids considered essential because the body must have all of them in the right amounts to function properly. Twelve of these are manufactured in the body but the other eight amino acids must be provided by the diet. Foods from an animal source such as milk or eggs often contain all these essential amino acids while a variety of plant products must be taken together to provide all these necessary protein components.
Fat supplies energy and transports nutrients. There are two families of fatty acids considered essential for the body: the omega-3 and omega-6 fatty acids. Essential fatty acids are required by the body to function normally. They can be obtained from canola oil, flaxseed oil, cold-water fish, or fish oil, all of which contain omega-3 fatty acids, and primrose or black currant seed oil, which contains omega-6 fatty acids. The U.S. diet often contains an excess of omega-6 fatty acids and insufficient amount of omega-3 fats. Increased consumption of omega-3 oils are recommended to help reduce risk of cardiovascular diseases and cancer and alleviate symptoms of rheumatoid arthritis, premenstrual syndrome, dermatitis, and inflammatory bowel disease.
Carbohydrates are the body's main source of energy and should be the major part of total daily intake. There are two types of carbohydrates: simple carbohydrates (such as sugar or honey) and complex carbohydrates (such as grains, beans, peas, or potatoes). Complex carbohydrates are preferred because these foods are more nutritious yet have fewer calories per gram compared to fat and cause fewer problems with overeating than fat or sugar. Complex carbohydrates are also preferred over simple carbohydrates by diabetics because they allow better blood glucose control.
Fiber is the material that gives a plant texture and support. Although it is primarily made up of carbohydrates, it does not have a lot of calories and usually is not broken down by the body for energy. Dietary fiber is found in plant foods such as fruits, vegetables, legumes, nuts, and whole grains.
There are two types of fiber: soluble and insoluble. Insoluble fiber, as the name implies, does not dissolve in water because it contains high amount of cellulose. Insoluble fiber can be found in the bran of grains, the pulp of fruit and the skin of vegetables. Soluble fiber is the type of fiber that dissolves in water. It can be found in a variety of fruits and vegetables such as apples, oatmeal and oat bran, rye flour, and dried beans.
Although they share some common characteristics such as being partially digested in the stomach and intestines and have few calories, each type of fiber has its own specific health benefits. Insoluble fiber speeds up the transit of foods through the digestive system and adds bulk to the stools, therefore, it is the type of fiber that helps treat constipation or diarrhea and prevents colon cancer. On the other hand, only soluble fiber can lower blood cholesterol levels. This type of fiber works by attaching itself to the cholesterol so that it can be eliminated from the body. This prevents cholesterol from recirculating and being reabsorbed into the bloodstream.
Vitamins and minerals
Vitamins are organic substances present in food and required by the body in a minute amount for regulation of metabolism and maintenance of normal growth and functioning. The most commonly known vitamins are A, B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folic acid), B12 (cobalamin), C (ascorbic acid), D, E, and K. The B and C vitamins are water-soluble, excess amounts of which are excreted in the urine. The A, D, E, and K vitamins are fat-soluble and will be stored in the body fat.
Minerals are vital to our existence because they are the building blocks that make up muscles, tissues, and bones. They also are important components of many life-supporting systems, such as hormones, oxygen transport, and enzyme systems.
There are two kinds of minerals: the major (or macro) minerals and the trace minerals. Major minerals are the minerals that the body needs in large amounts. The following minerals are classified as major: calcium, phosphorus, magnesium, sodium, potassium, sulfur, and chloride. They are needed to build muscles, blood, nerve cells, teeth, and bones. They are also essential electrolytes that the body requires to regulate blood volume and acid-base balance.
Unlike the major minerals, trace minerals are needed only in tiny amounts. Even though they can be found in the body in exceedingly small amounts, they are also very important to the human body. These minerals participate in most chemical reactions in the body. They are also needed to manufacture important hormones. The following are classified as trace minerals: iron, zinc, iodine, copper, manganese, fluoride, chromium, selenium, molybdenum, and boron.
Many vitamins (such as vitamins A, C, and E) and minerals (such as zinc, copper, selenium, or manganese) act as antioxidants. They protect the body against the damaging effects of free radicals. They scavenge or "mop up" these highly reactive radicals and change them into inactive, less harmful compounds. In so doing, these essential nutrients help prevent cancer and many other degenerative diseases, such as premature aging, heart disease, autoimmune diseases, arthritis, cataracts, Alzheimer's disease, and diabetes mellitus.
Water helps to regulate body temperature, transports nutrients to cells, and rids the body of waste materials.
Unlike plants, human beings cannot manufacture most of the nutrients that they need to function. They must eat plants and/or other animals. Although nutritional therapy came to the forefront of the public's awareness in the late twentieth century, the notion that food affects health is not new. John Harvey Kellogg was an early health-food pioneer and an advocate of a high-fiber diet. An avowed vegetarian, he believed that meat products were particularly detrimental to the colon. In the 1870s, Kellogg founded the Battle Creek Sanitarium, where he developed a diet based on nut and vegetable products.
Good nutrition helps individuals achieve general health and well-being. In addition, dietary modifications might be prescribed for a variety of complaints including allergies, anemia, arthritis, colds, depressions, fatigue, gastrointestinal disorder, high or low blood pressure, insomnia, headaches, obesity, pregnancy, premenstrual syndrome (PMS), respiratory conditions, and stress.
Nutritional therapy may also be involved as a complement to the allopathic treatments of cancer, diabetes, and Parkinson's disease. Other specific dietary measures include the elimination of food additives for attention deficit hyperactivity disorder (ADHD), gluten-free diets for schizophrenia, and dairy-free for chronic respiratory diseases.
A high-fiber diet helps prevent or treat the following health conditions:
- High cholesterol levels. Fiber effectively lowers blood cholesterol levels. It appears that soluble fiber binds to cholesterol and moves it down the digestive tract so that it can be excreted from the body. This prevents the cholesterol from being reabsorbed into the bloodstream.
- Constipation. A high-fiber diet is the preferred non-drug treatment for constipation. Fiber in the diet adds more bulk to the stools, making them softer and shortens the time foods stay in the digestive tract.
- Hemorrhoids. Fiber in the diet adds more bulk and softens the stool, thus reducing painful hemorrhoidal symptoms.
- Diabetes. Soluble fiber in the diet slows down the rise of blood sugar levels following a meal and helps control diabetes.
- Obesity. Dietary fiber makes a person feel full faster.
- Cancer. Insoluble fiber in the diet speeds up the movement of the stools through the gastro-intestinal tract. The faster food travels through the digestive tract, the less time there is for potential cancer-causing substances to work. Therefore, diets high in insoluble fiber help prevent the accumulation of toxic substances that cause cancer of the colon. Because fiber reduces fat absorption in the digestive tract, it may also prevent breast cancer.
- A diet low in fat also promotes good health and prevents many diseases. Low-fat diet can help treat or control the following conditions:
- Obesity. High fat consumption often leads to excess caloric and fat intake, which increases body fat.
- Coronary artery disease. High consumption of saturated fats is associated with coronary artery disease.
- Diabetes. People who are overweight tend to develop or worsen existing diabetic condition due to decreased insulin sensitivity.
- Breast cancer. A high dietary consumption of fat is associated with an increased risk of breast cancer.
The four basic food groups, as outlined by the United States Department of Agriculture (USDA) are:
- dairy products (such as milk and cheese)
- meat and eggs (such as fish, poultry, pork, beef, and eggs)
- grains (such as bread cereals, rice, and pasta)
- fruits and vegetables
The USDA recommendation for adults is that consumption of meat, eggs, and dairy products should not exceed 20% of total daily caloric intake. The rest (80%) should be devoted to vegetables, fruits, and grains. For children age two or older, 55% of their caloric intake should be in the form of carbohydrates, 30% from fat, and 15% from proteins. In addition, saturated fat intake should not exceed 10% of total caloric intake. This lowfat, high-fiber diet is believed to promote health and help prevent many diseases, including heart disease, obesity, and cancer.
Allergenic and highly processed foods should be avoided. Highly processed foods do not contain significant amounts of essential trace minerals. Furthermore, they contain lots of fat and sugar as well as preservatives, artificial sweeteners and other additives. High consumption of these foods causes build up of these unwanted chemicals in the body and should be avoided. Food allergy causes a variety of symptoms including food cravings, weight gain, bloating, water retention. It may also worsen chronic inflammatory conditions such as arthritis.
An enormous body of research exists in the field of nutrition. Mainstream Western medical practitioners point to studies that show that a balanced diet, based on the USDA Food Guide Pyramid, provides all of the necessary nutrients.
The Food Guide Pyramid recommends the following daily servings in six categories:
- Grains: Six or more servings.
- Vegetables: Five servings.
- Fruits: Two to four servings.
- Meat: Two to three servings.
- Dairy: Two to three servings.
- Fats and oils: Use sparingly.
Individuals should not change their diets without the advice of nutritional experts or health care professionals. Certain individuals especially children, pregnant and lactating women, and chronically ill patients should only change their diets under professional supervision.
It is best to obtain vitamins and minerals through food sources. Excessive intake of vitamins and mineral supplements can cause serious physiological problems.
The following is a list of possible side effects resulting from excessive doses of vitamins and minerals
- vitamin A: birth defects, irreversible bone and liver damage
- vitamin B1: deficiencies in B2 and B6
- vitamin B6: damage to the nervous system
- vitamin C: affects the absorption of copper; diarrhea
- vitamin D: hypercalcemia (abnormally high concentration of calcium in the blood)
- phosphorus: affects the absorption of calcium
- zinc: affects absorption of copper and iron; suppresses the immune system
Research and general acceptance
Due to the large volume of scientific evidence demonstrating the benefits of the low-fat, high-fiber diet in disease prevention and treatment, this diet has been accepted and advocated by most health care practitioners.
Bruce, Debra Fulghum, and Harris H. McIlwain. The Unofficial Guide to Alternative Medicine. New York: Macmillan, 1998.
Cassileth, Barrie R. The Alternative Medicine Handbook. New York: W.W. Norton, 1998.
Credit, Larry P., Sharon G. Hartunian, and Margaret J. Nowak. Your Guide to Complementary Medicine. Garden City Park, NY: Avery Publishing Group, 1998.
U.S. Preventive Services Task Force Guidelines. "Counseling to Promote a Healthy Diet." Guide to Clinical Preventive Services. 2nd edition. <<a href="http://cpmcnet.columbia.edu/texts/gcps/gcps0066.html">http://cpmcnet.columbia.edu/texts/gcps/gcps0066.html>.
Winick, Myron. The Fiber Prescription. New York: Random House, Inc., 1992.
Halbert, Steven C. "Diet and Nutrtion in Primary Care: From Antioxidants to Zinc." Primary Care: Clinics in Office Practice (December 1997): 82543.
Turner, Lisa. "Good 'n Plenty." Vegetarian Times (February 1999):48
Vickers, Andrew, and Catherine Zollman. "Unconventional approaches to nutritional medicine." British Medical Journal (November 27, 1999): 1419.
American Association of Nutritional Consultants. 810 S. Buffalo Street, Warsaw, IN 46580. (888) 828-2262.
American Dietetic Association. 216 W. Jackson Boulevard, Suite 800, Chicago, IL 60606-6995. (800) 366-1655. <<a href="http://www.eatright.org/">http://www.eatright.org/>.
Nutrition (Encyclopedia of Public Health)
Few subjects are more important to public health than food. One of the major ways in which humans interact with their environment is through our food. The science of nutrition has developed through the study of the components of foods that are required to sustain life and to maintain health. Improper diet can cause disease if important nutrients are missing from the diet, and inappropriate dietary practices can increase the risk of certain diseases.
Essential nutrients are substances that must be in the human diet to support life. These essential nutrients include vitamins, inorganic elements, essential amino acids, essential fatty acids, and a source of energy, and water. A lack of a nutrient or an insufficient amount of a nutrient can result in a deficiency disease that can be life threatening in extreme cases. The essential nutrients are widely distributed in foods and most people can obtain sufficient amounts of them if they consume a varied diet.
ELEMENTS OF HUMAN NUTRITION
Energy. Most of the food consumed is used by the body to supply energy. The body is able to digest and absorb into the blood stream components of carbohydrates, fats, and protein that can be metabolized by the body to release energy. Energy is used to maintain body temperature, support metabolic processes, and to support physical activity. People are generally in a state of energy balance, that is, they consume as much energy as they use to support their bodies and daily living. They tend to gain weight if they are in positive energy balance, or lose weight if they take in less than they expend. Most excess energy is stored by the body as fat. Energy needs are usually expressed in kilocalories, but in much of the world's scientific literature, energy expenditure is expressed in joules or kilojoules (1 kilocalorie equals 4.184 kilojoules).
The energy expended by the body when at rest is quite constant between individuals and can be
|Energy Expenditure during Selected Activities|
|Activity||Kcal expended per hour1|
|1These values represent above resting metabolic rate for a 70 kg person.|
|SOURCE: Powers, S. K., and E. T. Howley, eds. (2000). Exercise Physiology, 4th ed., New York: McGraw-Hill.|
|Walking, 2 to 2.5 miles per hour (mph)||18555|
|Walking, 5 mph||555|
|Jogging 5.5 mph||655|
|Cross country skiing||600|
estimated quite closely by prediction equations that take into account age, sex, and body weight. The resting metabolic weight of a 70-kilogram (154-lb.) man, for example, is estimated to be 1750 kilocalories per day, and for a 58-kilogram (128-lb.) woman, 1350 kilocalories per day. The total daily energy needs are related to the amount of physical activity expended in the course of everyday life. A person whose life style involves light amounts of activity may have a total energy expenditure of about one and one-half times their resting metabolic rate, while a person who is engaged in very intense physical activity may expend over twice as much energy as their resting metabolic rate in the course of twenty-four hours. Exercise can increase the metabolic rate considerably, depending on the type and duration of the activity. The amount of energy expended by certain types of physical activity is shown in Table 1.
Protein. The principal structural components of body soft tissues are proteins, which are made by the body from amino acids. The amino acids along with the nucleic acids are the principle nitrogen-containing components of the body and of most foods. The enzymes that regulate most body processes are also proteins. The body can synthesize many of the amino acids needed for protein syntheses, but some amino acids must be obtained from the proteins in the diet. The dietary essential amino acids for humans are threonine, valine, leucine, isoleucine, methionine, lysine, histidine, and tryptophan. Two others can only be formed from essential amino acids: tryosine from phenylalanine, and cystine from methionine. Human dietary protein requirements are quite modest. An adult man of average weight is estimated to need about sixty-three grams of protein per day, while an average woman is estimated to need about fifty grams. The protein must supply the essential amino acids required by humans and sufficient total nitrogen to allow syntheses of the other amino acids required for protein synthesis.
Fats. Fats are synthesized from carbohydrates, but the body is unable to make certain fatty acids, which are components of fats. These essential fatty acids, notably linoleic and linolenic acid, must be supplied by dietary fats. Fats that are solid at room temperature, such as butter or lard, usually contain high amounts of saturated fatty acids such as palmitic or stearic acid. Fats that are liquid at room temperature such as vegetable oils are higher in unsaturated fatty acids, which include oleic acid as well as the linoleic and linolenic acid. Fat is the most concentrated source of energy available to humans, supplying about nine kilocalories per gram of dietary fat, compared to four kilocalories per gram of carbohydrate and protein. Fat is also the principal storage form of energy in the body.
Vitamins. Vitamins are a diverse group of dietary essentials that have important functions in the body. The vitamins known to be required by humans are listed in Table 2. Many of them are components of co-enzymes, molecules that are required for some enzymes to carry out certain metabolic processes. Others, such as vitamin E and vitamin C, act as antioxidants, protecting body components from damage from oxygen needed by the body for metabolism. Some are more like hormones, such as vitamin D, which regulates the absorption of calcium from the intestine and the formation of bones. Vitamin D can actually be formed by the action of ultraviolet light from the sun on vitamin D precursors found in the skin, but since this synthesis may not be sufficient at times, humans need a dietary source of vitamin D. Vitamin A is a component of visual pigments in the eye that respond to light stimuli and are essential for sight.
A deficiency of a vitamin may result in a characteristic deficiency disease related to the body function affected by the lack of the vitamin. Vitamin D deficiency can cause soft bones in children, a condition called rickets; vitamin A deficiency
|Vitamins and Inorganic Elements Required in Human Diets to Support Life and Maintain Health|
|SOURCE: Powers, S. K., and E. T. Howley, eds. (2000). Exercise Physiology, 4th ed., New York: McGraw-Hill.|
|Vitamin A (retinol, retinal, retinoic acid)||
|Vitamin C (ascorbic acid)||Potassium|
|Vitamin D (D3 cholecalciferol, D2 ergocalciferol)||
|Vitamin K (menaquinones, phylloquinone)||
|Vitamin E (tocopherols)||Iodine|
|Vitamin B6 (pyridoxine)||Zinc|
|1Choline can be synthesized by the body but recent evidence suggests that dietary choline may be needed at some stages of the life cycle.||In addition to these elements, substantial evidence indicates that arsenic, nickel, silicon, and vanadium have important physiological functions that may make them nutritional essentials. They are required in very small amounts and a dietary deficiency has not been convincingly described.|
may cause night blindness and even blindness in its more severe form. Many of the vitamins have multiple functions in the body, and deficiency diseases can be severely debilitating in severe cases. Vitamins are required in very small amounts by the body. Only a few micrograms of vitamin B12is required each day, while vitamin C requirements may be from sixty to one hundred milligrams per day.
Inorganic elements. Humans also require several inorganic elements as components of the diet. The inorganic elements known to be required by humans are listed in Table 2. These elements may have a structural function, such as calcium and phosphorus, which are needed for bone synthesis, or they may have a catalytic function similar to some of the vitamins. They are required for the action of many enzymes in the body. Sodium and potassium are essential for fluid balance. Iodine is an essential component of thyroxin, the hormone produced by the thyroid gland. Some of the inorganic elements are required in extremely small quantities, only micrograms per day, while other elements may be needed in higher amounts. Soils vary in their content of some of the trace elements, and plants grown in some areas may be deficient in an essential element. This has been true for iodine, where a deficiency is still observed in many areas of the world, and selenium, where geographically based human deficiency disease has been observed.
In the United States, the National Academy of Sciences, through the National Research Council and The Institute of Medicine, has convened expert groups since 1941 to establish nutrition recommendations to be used by individuals and institutions for planning nutritionally adequate diets. These groups have established recommended dietary allowances (RDAs) as the daily dietary intake level for a specific nutrient that is sufficient to meet the nutritional requirements of nearly all (978 percent) individuals in the life stage and gender group specified. In the most recent recommendations, dietary reference intakes (DRIs) have been specified that have attempted to estimate average nutrient requirements, RDAs, and an upper limit of safe nutrient intake. Where data are not sufficient to set a precise RDA, new recommendations called adequate intake (AI) define a recommendation for some nutrients.
The RDAs and AIs are used to plan diets for groups in hospitals, the military, large institutions, to set standards for government food programs such as school lunches, to establish nutritional labeling, and for counseling individuals. Similar dietary recommendations have been made by expert groups convened in many countries and also by international organizations such as the World Health Organization and the Food and Agricultural Organization of the United Nations. These recommendations are periodically revised to include information from most recent research findings. The latest recommendations for dietary reference intakes can be obtained in the United States from the National Academy Press, 2101 Constitution Avenue, NW, Washington, D.C. 20418.
Recommendations have been established for most nutrients where sufficient research data are available to make reliable estimates. The nutrient recommendations are given for different age groups and are differentiated by sexes because of different nutritional needs at different stages of life. Infants and young children who are growing rapidly have different nutrient needs compared to adults. Women who are menstruating need more iron to replace blood lost in the menstruation compared to postmenopausal women or men. Similarly, there are special needs for pregnant and lactating women. There is increasing evidence accumulating about the needs of the elderly, and nutrition recommendations now include a category for individuals over seventy years of age.
Recent revisions of nutrition recommendations have taken into account public health concerns about osteoporosis, a condition in which bone mineral is lost and older individuals become more vulnerable to bone fractures. New recommendations stress the importance of maintaining a high level (1200 mg/day) of calcium intake by both men and women over fifty years of age in an attempt to reduce loss of bone mineral. Similarly, recommendations for folic acid intake have also been revised to stress the importance of sufficient folic acid consumption by women who may become pregnant. Insufficient folic acid has been associated with a higher incidence of birth defects. The concern for adequate intake of folic acid led to the fortification of enriched grain products with folic acid in the United States beginning in 1998.
Nutrient recommendations also take into consideration the efficiency by which nutrients are digested and absorbed from foods. The form in which iron is ingested has a major influence on how much food iron is absorbed into the body. Iron in animal products is well absorbed because it is found as a component of hemoglobin or muscle pigments, while iron in plants, found as inorganic salts, is poorly absorbed. Some components of plants, such as phytic acid and tannins, also interfere with iron absorption. Therefore, dietary recommendations for iron intake must consider the availability of iron in the foods being consumed.
PUBLIC HEALTH ISSUES
In the early part of the twentieth century, nutritional disorders were common. Pellagra, a disease caused by a deficiency of nicotinic acid, was widespread in the southern United States. Rickets, from vitamin D deficiency, was common, and goiters from iodine deficiency were widespread. Iron-deficiency anemia and riboflavin deficiency were frequently observed. In parts of Asia, beriberi, a disease caused by thiamin deficiency, was a public health problem. The discovery and characterization of the vitamins made it possible to produce them in large amounts, and the enrichment of grain products with niacin, riboflavin, thiamine, and iron largely eliminated B-vitamin deficiencies in the United States as a public health problem. Similarly, the addition of vitamins A and D to milk provided protection from deficiency of the nutrients. The use of iodized salt essentially eliminated goiter from the U.S. population.
Unfortunately, nutritional deficiencies have not been eliminated from much of the world even today. A combination of poor diet, poor sanitation, and lack of safe water leading to frequent intestinal infections, causes more than 200 million of the world's children to be shorter and weigh less than children in good environments at the same age. These malnourished children are often born underweight from mothers who are also underweight and of poor nutritional status. Measures of the degree of malnutrition that are frequently used include a comparison of a child's weight for age, height for age, and weight for height with norms established by similar measurements on a well-nourished population of children. A usual convention classifies a child whose weight for age is more than two standard deviations below the standard as malnourished, and those three standard deviations below the standard are usually considered severely malnourished. The most vulnerable time for growth faltering in children is the period from six months of age to two years, when breast feeding stops and weaning foods are introduced. A combination of poor weaning foods, exposure to contaminated water, and poor sanitation that results in frequent bouts of diarrhea and the occurrence of other childhood diseases contributes to the poor growth of children after weaning.
The United Nations estimates that more than two-hundred million of the world's children are stunted, with the largest numbers being found in South Asia and in Africa. Similarly, about 4 percent of the world's population is considered at risk for iodine deficiency disorders including goiter, cretinism, and mental retardation. Vitamin A deficiency is estimated to affect about 3.3 million children in the world. Iron deficiency anemia is also the most prevalent nutritional deficiency in the world. Over 90 percent of those effected live in developing countries. The United Nations has estimated that severe anemia is a contributing factor to 50 percent of maternal deaths in developing countries.
Nutritional deficiencies are common in the refugees displaced by wars and natural disasters. Assistance is provided by the United Nations High Commissioner for Refugees to more than 26 million people world wide, and there are other internally displaced people in the world that may number as many as 31 million. The difficulty of providing food for these displaced groups puts them at risk for nutritional deficiencies.
Nutritional deficiencies are rare in most industrialized nations in Europe, Asia, and the Americas, and among the higher income groups of the developing world. The public health issues related to nutrition in these nations are concerned with overonsumption of energy, inadequate levels of activity, and improper food choices. Dietary practices are known to be risk factors for severe chronic diseases, including hypertension, atherosclerotic cardiovascular disease, and several types of cancers. The amount and type of fats seem to influence the risk of atherosclerotic cardiovascular diseases and to risk of certain forms of cancer. The consumption of saturated fatty acids and trans fatty acids found in certain hydrogenated cooking fats increases the levels of serum total cholesterol and cholesterol associated with serum low density lipoproteins (LDL) and thus increases the risk of artheriosclerosis and coronary heart disease. Diets high in fruits, vegetables, legumes, and cereal products are associated with a lower occurrence of coronary heart disease and certain cancers.
Genetic variations occur among individuals in their response to food. Variations in various blood lipoprotein components can effect an individual's response to dietary fat and cholesterol, and risk of coronary heart disease. There appears to be a genetic component to susceptibility to obesity. As more information is known about the human genome, it may be possible to predict more accurately individual risks for disease, and the dietary factors that may modify this risk.
Obesity. Dietary patterns that are characterized by the consumption of energy-rich, high-fat foods are considered to be factors contributing to obesity, particularly when the high intake of energy is not accompanied by appropriate physical activity. Obesity in adults is defined by reference to the body mass index (BMI), a relationship that takes into account both height and body weight. The BMI is calculated as weight in kilograms/height in meters squared. In pounds and inches it is calculated by weight (pounds)/height (inches)2704.5. A person with a body mass index between 20 to 25 is considered in the normal range, while a body mass index of 25 to 30 is considered overweight, and over 30 is considered obese.
The prevalence of obesity in the United States has increased markedly in recent years. The prevalence of overweight children ages six to eleven in surveys conducted in the early 1970s was 6.5 percent of males and 4.9 percent for females. By 1988994, the prevalence of overweight in this age grouping had increased to 11.4 percent and9.9 percent for males and females respectively. On the basis of surveys carried out between the years 1988 and 1994, more than 50 percent of American adults were considered overweight on the basis of having a BMI greater than 25. In further surveys, 17.9 percent of U.S. adults were considered obese in 1988, compared with 12 percent in 1991. The increasing prevalence of obesity is of considerable public health concern as excess weight is associated with greater risk of mortality, non-insulin dependent Type II diabetes mellitus, hypertension, stroke, osteo-arthritis, and some cancers. The annual number of deaths attributed to obesity in the United States has been estimated at more than 280,000 persons.
The control of obesity is difficult, and weight reduction is difficult to maintain. The most effective weight loss schemes seem to be those that reduce weight slowly, from one-half to one pound per week, and that involve both reduction in energy intake and an increase in physical activity. For overweight individuals, a reduced intake of from 300 to 500 kilocalories per day should result in a loss of one-half to one pound per week, while severely obese individuals may need to reduce energy intake by 500 to 1000 kilocalories per day to achieve a one to two pound per week weight loss.
|Dietary Guidelines for Americans|
|SOURCE: From the United States Department of Agriculture/Department of Human Services: Dietary Guidelines for Americans 2000.|
|Aim for fitness|
|Build a Healthy Base|
Dietary guidelines. The concern for appropriate food choices have led many countries to issue dietary guidelines that provide advice that goes beyond the recommendations for individual nutrients covered by the recommended dietary allowances. The year 2000 dietary guidelines for Americans are shown in Table 3. These are issued by the U.S. Department of Agriculture and the U.S. Department of Health and Human Services and are revised about every five years. This publication represents the only official dietary advice to consumers by the U.S. Government. The full text of the bulletin provides more detailed advice on food choices. Many countries have published similar dietary guidelines to guide food choices to reduce the dietary risk factors associated with chronic disease.
To give advice to consumers regarding appropriate food choices to implement dietary guidelines, food guides have been developed. One of the most popular representations of a food guide is the dietary pyramid that has been published by the U.S. Department of Agriculture and the Department of Human Services. This food guide illustrates the importance of building a healthy diet on a base of cereal-based foods supplemented liberally with fruits and vegetables. Foods high in protein and fat should be consumed sparingly. The pyramid provides the number of recommended daily servings of the food groups.
Food supplies. The world population is projected to increase about 25 percent from the year 2000 to 2020, to about seven and one-half billion people. Most of this increase is projected to be in developing countries located in the tropical zones of the earth. The population of Asia is projected to increase by 800 million, and the population of Africa is projected to double. The International Food Policy Research Institute (IFPRI) has projected that food production will be able to increase such that the world per capita food available will supply about 2,900 kilocalories per person per day in the year 2020, compared to 2,700 kilocalories in 1993. The equitable distribution of food supplies will remain a major problem. The daily food available in sub-Saharan Africa is projected to supply only about 2,300 kilocalories per capita in the year 2020, barely sufficient to support a productive life. IFPRI estimates that one out of every four of the world's children will be malnourished in the year 2020. To achieve the projected increase in food supplies, continued improvements in crop yields will be necessary.
In contrast to the limited food supplies in many developing nations, developed countries are projected to have a food supply that will provide 3,470 kilocalories per capita per day in the year 2020. The U.S. Department of Agriculture indicates that the available food in the United States in 1994 provided 3,800 kilocalories per capita. This food supply provided annually 193 pounds of red meat, poultry, and fish, 585 pounds of dairy products, 194 pounds of cereal products, 151 pounds of fresh, canned, or dried fruits, 208 pounds of fresh, canned, frozen, dried, or fried vegetables and pulses, and 147 pounds of sugar. These figures represent food availability and do not represent actual consumption or account for wastes and losses in marketing and food preparation. Even with the variety of food available, consumers in the United States do not generally meet the dietary guidelines and food guide recommendations. For example, in food consumption surveys, only 38 percent of those surveyed reported consuming the recommended number of servings per day of cereals, 41 percent of the servings of vegetables (heavily weighted toward potatoes and starchy vegetables), and 23 percent of the servings of fruits. The reported diets provided 33 percent of the energy from fats and 11 percent from saturated fats. Food choices by consumers appear to depend on a variety of factors, such as cost, food preferences, convenience of preparation, and cultural norms, in addition to perception as to effects on health.
Food safety. In addition to providing nutrients, food can also potentially be a source of harm to a consumer. Hazards associated with food include microbiological pathogens, naturally occurring toxins, allergens, intentional and unintentional additives, modified food components, agricultural chemicals, environmental contaminants, and animal drug residues. It has been estimated that more than 80 million cases of food-borne illness occur annually in the United States, resulting in more than 9,000 deaths, primarily from microbiological contamination. The transformation of a safe food into a potentially dangerous one can occur anywhere in a food system that consists of producers, shippers, processors, wholesalers, retailers, and consumers.
An effective food safety system requires regulation, surveillance, consumer education, and continued research to detect and prevent food-borne illnesses. The increase in world trade in food also involves international dimensions in food safety issues. Import regulations dealing with food safety may also have the effect of restricting access to markets, and food safety becomes an issue in world trade.
The United States has a complex system of food-safety regulation. The Food and Drug Administration (FDA) is responsible for domestic and imported foods in interstate commerce except for poultry and meat products. The FDA has responsibility for standards for food labeling, inspects food-processing plants, and regulates food animal drugs and feed additives and all food additives. The Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture (USDA) inspects meat and poultry products to ensure they are safe and correctly marked, labeled, and packaged. The Environmental Protection Agency (EPA) licenses pesticide products and establishes tolerances for pesticide residues in food products and animal feeds. The Centers for Disease Control and Prevention (CDC) are responsible for surveillance of illnesses associated with food consumption in association with the FDA and the USDA. These agencies also collaborate with state and local public health agencies that are concerned with food safety.
The consumption and preparation of food also has great social and cultural significance, contributing to the daily enjoyment of life. Public health concerns about dietary practices often must compete with these values as an individual makes food choices. This makes the issues associated with food and nutrition more complex than the medical and public health issues discussed here.
MALDEN C. NESHEIM
(SEE ALSO: Blood Lipids; Energy; Foods and Diets; Nutrition in Health Departments)
Institute of Medicine, Food and Nutrition Board (1989). Diet and Health: Implications for Reducing Chronic Disease. Washington, DC: National Academy Press.
(1997). Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press.
(1997). Dietary Reference Intakes: Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press.
Institute of Medicine, National Research Council (1998). Ensuring Safe Food. Washington, DC: National Academy Press.
Mokdad, H. H.; Serdula, M. K.; Dietz, W. H.; Bowman, B. A.; Marks, J. S.; and Koplan, J. P. (1999). "The Spread of the Obesity Epidemic in the United States 1991998." Journal of the American Medical Association 282:1519522.
Must, A.; Spadano, J.; Coakley, A.; Field, E.; Colditz, G.; and Dietz, W. H. (1999). "The Disease Burden Associated with Overweight and Obesity." Journal of American Medical Association 282:1523529.
National Research Council, Food and Nutrition Board (1989). Recommended Dietary Allowances, 10th edition. Washington, DC: National Academy Press.
Pandya-Lorch, R.; Andersen, P. P.; and Rosegrant, M. (1997). The World Food Situation: Recent Developments, Emerging Issues, and Long Term Prospects. Washington, DC: International Food Policy Research Institute.
Shils, M. E.; Olson, J. A.; and Shike, M. (1994). Modern Nutrition in Health and Disease, Vols. 1 and 2, 8th edition. Philadelphia, PA: Lea and Febiger.
(1999). Modern Nutrition in Health and Disease, 9th edition. Baltimore, MD: Williams and Wilkins.
Stipanuk, M. (2000). Biochemical and Physiological Aspects of Human Nutrition. Philadelphia, PA: W. B. Saunders Company.
Sub-Committee on Nutrition (ACCI/SCN) United Nations Administrative Committee on Coordination (1997). Third Report on the World Nutrition Situation. Geneva: World Health Organization.
Triano, R. P., and Flegal, K. M. (1998). "Overweight Children and Adolescents: Description, Epidemiology, and Demographics." Pediatrics 101:49703.
United Kingdom Department of Health (1991). Dietary Reference Values for Food Energy and Nutrients for the United Kingdom: Report of the Panel on Dietary Reference Values of the Committee on Medical Aspects of Food Policy. London: HMSO.
United States Department of Agriculture and the United States Department of Health and Human Services (2000). Nutrition and Your Health: Dietary Guidelines for Americans. Home and Garden Bulletin no. 232, 5th edition. Washington, DC: United States Government Printing Office.
U.S. Department of Agriculture (1992). The Food Guide Pyramid. Home and Garden Bulletin no. 252. Washington, DC: Human Nutrition Information Service.
World Health Organization (1985). Energy and Protein Requirements: Report of a Joint FAO/WHO/UNU Expert Consultation. WHO Technical Report Series 724. Geneva: Author.
Nutrition (Encyclopedia of Food & Culture)
NUTRITION. Food is comprised of nutrients that are classified by their role in the body: the energy-yielding macronutrients (carbohydrates, protein, and fat), the essential micronutrients (vitamins, minerals, and water), and numerous other components. Although micronutrients do not supply energy to fuel the body, they are indispensable for the proper functioning of the metabolic and regulatory activities in the body. Other nonessential nutrients, such as flavonoids, phytoestrogens, carotenoids, and probiotics, also may have important health-promoting properties, and investigations are ongoing. The daily intake of a variety of foods provides energy and nutrients that are essential to the health and well-being of an individual. The relationships among food intake, nutrition, and health define the field of nutrition. More fully, nutrition is the study of food, its nutrients and chemical components, and how these constituents act and interact within the body to affect health and disease.
The scope of the field has grown in recent years and the boundaries between the science of nutrition and many other biological sciences have blurred. For example, the science of nutrition includes chemistry to study how food ingredients interact with each other; physiology to investigate how nutrients within food are assimilated into body tissues; engineering to design new fortified foods; anthropology to explore why we chose to eat certain foods in centuries past; and psychology to determine what attitudes and behaviors influence our dietary patterns today. Nutritionists often have either a college or advanced degree in nutrition or a related field, whereas clinical (human) nutrition specialists will have graduate degrees, which may include medicine, and have completed an examination for certification. Registered dietitians are nutrition professionals who are often responsible for applying nutritional science to clinical practice to promote health and treat disease. Dietitians frequently work in hospitals but also may be employed in universities, public health departments, restaurants, the food industry, and exercise facilities. Similarly, given the broad scope of the field, other nutrition professionals include but are not limited to physicians, biochemists, anthropologists, epidemiologists, geneticists, food scientists, and engineers.
For this review, the field of nutrition is divided into three major categories: (1) nutrition in research, (2) nutrition in clinical practice, and (3) nutrition in policy and education. An overview of nutritional research is presented, from how nutrients interact within the body and among themselves (nutritional biochemistry), to the investigation of the relationships between specific foods or food groups and the health status of populations (nutritional epidemiology). Research findings in the field provide the information needed to guide nutrition practice for the care of individuals as well as large groups of people. The development of nutrition policy comes from both research and clinical practice advances. Concise descriptions of each are given and a brief history of the field and projected directions of the future of the field are offered.
Nutrition: A Historical Perspective
Numerous advances in the field of nutrition have occurred within the last century. The major focus of nutrition research and practice shifted from concern over which foods are required to avoid nutritional deficiencies and overt illness, to what foods and supplements may be consumed to promote optimal health. Functional foods are a part of the vocabulary, and energy bars, herbal remedies, and nutritional supplement products are now widely available.
In biblical times certain foods were understood to have special healing properties; however, the concept of nutrients as essential for health is relatively new. Recent discoveries in the field have been dependent on the development of scientific methods to analyze nutrient content and interactions. Therefore, though some vitamins were understood to be essential in the early part of the twentieth century, trace elements such as zinc and selenium were not considered essential for humans until the 1970s.
As the field of nutrition has developed, it has also expanded. In 1950 the history of nutrition science during the two previous centuries was summarized by Dr. Elmer McCollum in just under five hundred pages. It would likely take ten volumes of such texts to encapsulate the nutrition-related findings and proceedings from the latter half of the twentieth century. Accomplishments in the field of nutrition over the last century are highlighted in five major eras: (1) food as energy, (2) micronutrient deficiency diseases, (3) nutrition in public policy, (4) nutrition and chronic disease, and (5) nutrition for optimal health.
Food as energy (1880920). By the end of the nineteenth century the major, energy-yielding components of foodrotein, fat, and carbohydratead been identified, and nutrition research, especially concerning the metabolism of proteins and the energy composition of foods, was flourishing. Much of this work had been conducted in animals; therefore, the human nutrition experiments performed by Dr. W. O. Atwater (1844907) and colleagues were particularly novel. From their studies, the energy yield of carbohydrate, protein, and fat was derived (4, 4, and 9 kcal per gram, respectively), values that are still used today. Dr. Atwater also developed the first human calorimeter in the United States to measure energy expenditure. However, it was a pair of medical doctors, James Harris and Francis Gano Benedict, who perfected this methodology to establish standards for the energy needs of healthy individuals. Energy expenditure was measured in approximately 250 healthy men and women at the Carnegie Institute Laboratory in Washington, D.C., and equations were derived from the data. The Harris-Benedict energy expenditure prediction equations for men and women, published in 1919, remain some of the most useful tools in clinical nutrition assessment today.
Micronutrient deficiency diseases (1920940). The period between 1920 and 1940 brought about a paradigm shift in the understanding of the etiology of some common diseases. Until this time it was thought that all disease resulted from poor sanitation and hygiene; therefore, bacteria, mold, and toxins were identified as the likely cause of disease. As Alfred Harper has suggested, "the concept that a disease might be caused by a deficit of a substance that was nutritionally essential was beyond the grasp even of most nineteenth-century physicians and scientists" (p. 217). In order to combat disease as well as increase shelf life, food was sterilized, milled, and polished to reduce the danger of ingesting bacteria, mold, and toxins. Despite these efforts, pellagra, beriberi, and infantile scurvy actually increased in prevalence. In a number of studies conducted by Dr. Joseph Goldberger from 1914 to the 1920s, where the diets of individuals suffering from pellagra were compared to those of healthy individuals, foods that decreased the presence of diarrhea and dementia in pellagrous individuals were identified. From his work it was later determined that pellagra was due to a diet poor in the vitamin niacin and not infection. At approximately the same time, Dr. Christiaan Eijkman (1858930) won a Nobel Prize in medicine (1929) for the discovery of the "antineuritic" vitamin thought to be responsible for curing beriberi. Through his experiments, in which chickens were fed human hospital diets, combined with studies of beriberi in prisoners who survived on polished rice, he hypothesized that the hull of the rice grain contained an antidote to the neurological disorder. Although not completely correct, his observations led to the discovery of the essential vitamin thiamin.
As Kenneth J. Carpenter summarized, "new technologies of food processing that have obvious advantages may also have a downside" (p. 227). While technology decreased infectious disease and increased the shelf life of food products, it inadvertently led to nutritional deficiencies. The heat-sterilization of cow's milk, which destroyed vitamin C, was related to the outbreak of infantile scurvy in well-to-do families. The practices of polishing rice and degerming corn to increase grain stability also led to increased prevalence of beriberi (thiamin deficiency) and pellagra (niacin deficiency), respectively.
Nutrition in public policy (1920964). One of the most fruitful periods in the history of public health nutrition followed on the coattails of World War I. It became possible to manufacture the micronutrients that had been identified by chemists as essential for health cheaply and efficiently. In 1922 the first of a series of public health efforts at eradicating nutrient deficiency in the United States was initiated by the voluntary addition of iodine to salt (see Table 1). The fortification of other foods was used to address rampant public health problems such as rickets (vitamin D), beriberi (thiamin), pellagra (niacin), and dental caries (fluoride). Since the initiation of fortification policies in the United States, clinically evident nutritional deficiencies have been virtually eliminated.
The first attempt at defining nutritional requirements was directed toward the prevention of nutrient deficiencies in military personnel during World War II. In the early 1940s the Food and Nutrition Board of the National Academy of Sciences reviewed the scientific evidence and developed the Recommended Dietary Allowances for energy, protein, and eight essential vitamins and minerals. The first national food supplementation program was initiated in 1946 (National School Lunch Act) to improve the dietary intake of children from economically disadvantaged families. Other national food assistance programs were added over the next fifty years.
Nutrition and chronic disease (1960990). The last forty years of the twentieth century saw continued discovery in the field of nutritional biochemistry and a new research emphasis on the role of nutrition in the cause of and treatment for chronic disease. Disease patterns shifted from infectious and nutrient deficiency diseases to increasing rates of cardiovascular disease, diabetes, cancer, and osteoporosis. Nutrient deficiencies, when present, were often secondary to restrictive dietary habits, economic deprivation, or the presence of another disease that altered nutrient metabolism. The more pressing problem now was the change in the American lifestyle and a dietary shift from too little to too much. Modern household technologies increased productivity in housework but decreased physical activity, and the home-cooked family meal became a thing of the past. Varied diets consisting of whole grains, fruits, and vegetables gave way to convenience foods resulting in a much higher consumption of fat and sugar. Results from the Framingham Heart Study were perhaps the first glimpse into the relationship between fat intake and cardiovascular disease and the realization that each type of fat plays a specific role in health and disease. During this era, links among fat intake, serum cholesterol, and cardiovascular disease were studied thoroughly, and the reasons for the increasing prevalence of obesity in the United States were explored. In 1985 Michael Brown and Joseph Goldstein were awarded the Nobel Prize in medicine for their work on the regulation of cholesterol metabolism and its influence on arteriosclerosis.
The essentiality of macrominerals (e.g., calcium, phosphorus, sodium) was understood in the 1850s. However, it was not until technological advances triggered an explosion of new research that trace and ultra-trace elements were identified as essential for humans. Working together, nutritionists, biochemists, biologists, immunologists, geneticists, and epidemiologists uncovered the mysteries behind minerals such as zinc, selenium,
|Significant policies and recommendations in nutrition (1901001)|
|Date||Nutrition policies and recommendations||Description|
|1917||Food Guide, "5 Food Groups"||Food groups included flesh foods, breads/cereals, butter/fats, fruits and vegetables, and sweets (USDA).|
|1922||Iodine fortification||Iodized salt was initially added to salt (60 mg/g salt) in Michigan, goiter virtually eradicated by 1927.|
|1932||Vitamin D fortification||Vitamin D was added to milk at a minimum of 400 IU/quart. Was also added to some margarine.|
|1941||Enrichment with iron, niacin, riboflavin, and thiamin||Iron, niacin, riboflavin, and thiamin were added to refined wheat flour, and eventually to bread, pasta, rice, and cereal grain products.|
|1943||Recommended Dietary Allowances, 1st edition (United States)||Purpose: "To serve as a guide for planning an adequate diet for every normal person." (FNB/NRC)|
|1945||Fluoride fortification||Voluntary artificial fluoridation of municipal water supply in the United States; currently, 62 percent of U.S. population drinks fluoridated water.|
|1946||Food Guide, "Basic 7"||Food groups included milk, meat, green/yellow vegetables, citrus fruits, potatoes/other vegetables, bread/cereal, and butter/margarine (USDA).|
|1946||National School Lunch Act||It provides nutritionally balanced, low-cost, or free lunches to nearly 27 million children each school day. The program was established under the National School Lunch Act, signed by President Harry S Truman.|
|1958||Daily Food Guide, "Basic 4"||Food groups included meat/eggs/fish, milk/dairy, fruit/vegetables, and bread/cereals (USDA).|
|1964||Food Stamp Act||The first Food Stamp Act was started as a pilot project in 1961. The current law was enacted in 1977 and is amended regularly by the Congress. Purpose is to end hunger and improve nutrition and health. It helps low-income households buy food for a nutritionally adequate diet.|
|1975||National School Breakfast Program||The School Breakfast program began as a pilot project in 1966 under the Child Nutrition Act. The purpose was to ensure that all children have access to a healthy breakfast at school to promote learning readiness and healthy eating behaviors. It provides nutritionally balanced, low-cost, or free breakfasts to 7.4 million children each school day.|
|1971974||National Health and Nutrition Examination Survey (NHANES)||The first of a series of surveys to assess the health and nutritional status of the U.S. population (NCHS/CDC).|
|1974||Special Supplementary Nutrition Program for Women, Infants, and Children (WIC)||Nonentitlement program designed to improve the intake of protein, vitamins A and C, calcium, and iron, to low-income, pregnant, and lactating women and children less than 5 years old.|
|1980||Dietary Guidelines for Americans: Nutrition and Your Health||First set of recommendations for individuals to guide food choices without specifying amounts (USDA/DHHS).|
|1985||Continuing Survey of Food Intakes of Individuals (CSFII)||The first of a series of surveys to provide information on the dietary status of the U.S. population and monitor changes in dietary intakes (ARS).|
|1988994||NHANES III||National Health and Nutrition Examination Survey, noted the significant increase in obesity in the United States (NCHS/CDC).|
|1989||RDA, 10th edition||Definition: the level of intake of essential nutrients that . . . meet the known nutrient needs of practically all healthy persons.|
|1989||VI. Diet and Health: Implications for Reducing Chronic Disease Risk||Thorough review of the evidence on which dietary guidelines are based. Specific evidence provided on intake of fat, fruit and vegetables, protein, salt, alcohol, calcium, fluoride, and physical activity (FNB).|
|1990||VII. Nutrition Labeling and Education Act (NLEA)||This act made standardized nutrition labeling on food products in the United States mandatory. There are now 11 health-related claims that are approved to be used in advertising on food packages (FDA).|
|1992||Food Guide Pyramid||Eating guide based on the RDA that also considered salt, fat, and sugar intake (USDA/HNIS).|
|1994||Dietary Supplement Health and Education Act (DSHEA)||Exempts any product labeled as a dietary supplement from FDA regulatory approval. Permits structure/function claims without prior FDA authorization.|
|1997||Dietary Reference Intakes (DRI)||This was the first in a series of revised recommendations now called DRI, which replaces the RDA. This report included recommendations for calcium, phosphorus, magnesium, vitamin D, and fluoride.|
|1998||Folate fortification||Fortification of all breads, pasta, rice, flour, and breakfast cereals with folate to decrease the risk of neural tube defects in women of childbearing age. Program initiated in United States, Mexico, and Canada.|
|1998||Dietary Reference Intakes (DRI)||Second series of the DRI for thiamin, riboflavin, niacin, vitamins B6 and B12, folate, pantothenic acid, biotin, and choline.|
|2000||Dietary Guidelines for Americans, 4th edition||The dietary guidelines are updated about every 5 years. They provide nontechnical suggestions for healthy dietary patterns and activity (USDA/DHHS).|
|2001||Dietary Reference Intakes (DRI)||Third series of the DRI for vitamins A and K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdemum, nickel, silicon, vanadium, and zinc.|
copper, molybdenum, and chromium. Scientists first recognized human zinc deficiency in the mid-1960s. Severely growth-retarded, young Middle Eastern men were anemic, extremely lethargic, and hypogonadal. Their diet consisted mainly of wheat bread with little animal protein. When their diets were supplemented with zinc, their lethargy, growth, and genital development improved.
Nutrition for optimal health (1990resent). In the understanding of nutrition, the American public experienced yet another paradigm shift in the 1990s. They wondered if all nutrients that provided a health benefit needed to fit the traditional definition of "essential nutrient." As a result of this question, herbal and botanical extracts, phytochemicals, and other alternative nutritional therapies to promote optimum health were explored. In 1999 the U.S. market for functional foods alone was estimated to be $6 billion (Hasler, p. 504) and it continues to grow by approximately 12 percent each year. The explosion of this market is likely due to the increase in social acceptance, changes in regulations, the booming economy of the 1990s, and the targeting of products to particular populations. The scientific validation of some therapies also is of increasing interest.
Pharmacological uses (larger amounts than required to prevent deficiencies) of essential nutrients are being explored. Although much of the current interest in megavitamin supplementation began in the 1990s, the work of Dr. Linus Pauling in the 1970s initiated the movement. Pauling was the only individual to be awarded two unshared Nobel prizes for his work in chemistry (1954) and peace (1962). In the field of nutrition, however, he is noted most for his unproven theories regarding the potential protective role of vitamin C on the common cold, cancer, and heart disease. Pauling himself reportedly took up to six hundred times the recommended daily amount of vitamin C. Given that many individuals also practice a "more must be better" approach, the national recommendations for nutrient intake now include guidelines for safe upper limits for individual nutrient intakes.
Nutrition in Research
Experimental nutrition research is one aspect of the science of nutrition. Nutrition research is conducted to answer questions raised both in clinical practice and policy. Research in nutrition can focus on individual cells, whole animals or humans, or entire populations, and often overlaps with research in genetics, biochemistry, molecular biology, toxicology, immunology, physiology, and pharmacology.
Nutritional biochemistry. Nutritional biochemistry is the backbone to the understanding of the structure and function of nutrients within food and the body. Nutrients serve as cofactors for enzymes, components of hormones, and participants in oxidation/reduction reactions through metabolic processes. Though required in small amounts, nutrients are essential for body growth, sexual development and reproduction, psychological well-being, energy level, and the normal functioning of most organ systems in the body. Nutritional biochemists study the functional roles of vitamins and minerals in the body, metabolic blocks that occur from deficiencies, the effects of hormones on nutrient metabolism, and interactions among nutrients within the body. In the 1990s a whole new area of research emerged that focuses on relationships between nutrition and genetics. An example of this type of study includes the identification of a genetic defect in folate metabolism (C677T), which increases a woman's risk of delivering a baby with a neural tube defect.
Food science. Food science is the study of the composition of food materials and the reaction of food to processing, cooking, packaging, and storage. Food science integrates knowledge of the chemical composition of food materials; their physical, biological, and biochemical behavior; the interaction of food components with each other and their environment; pharmacology and toxicology of food materials, additives, and contaminants; and the effects of manufacturing operations, processes, and storage conditions.
The potential beneficial role of functional foods in the American diet has gained attention and recent food science research focuses on the development of such foods. Functional foods are generally defined as those that provide health benefits beyond basic nutrition, and include fortified, enriched, or enhanced foods, and whole foods, which have high levels of protective nutrient components. Examples of these foods include orange juice with added calcium or echinacea, or snack foods with antioxidants, fruit-flavored candy with vitamin C, various soy products, and margarine with added plant sterols. Factors that drive the market for such foods include a growing general public interest in nutrition and its impact on health, an aging population that is more concerned with health, research findings receiving media attention, and an increasingly unregulated consumer food market.
Human nutrition. Human nutrition, or clinical nutrition, research is that which focuses on the study of nutrients within the living human body. Although biochemical studies are extremely informative, until the nutrient is added to or depleted from the diet, the effects on individuals can only be hypothesized. Human nutrition research includes the study of individual nutrient requirements (e.g., nutrient intake assessment, energy expenditure assessment, nutrient turnover balance studies, and nutrient bioavailability), the effects of nutrients on body growth (e.g., body composition techniques, anthropometry, pubertal assessment), and the dietary, physiological, or disease factors that influence nutrient requirements. In the 1990s one important human nutrition study found that increasing folic acid intake in young women reduces the incidence of neural tube defects (spina bifida) in their babies.
Nutritional epidemiology. Nutritional epidemiology is the science of systematically studying the relationships between food choices and health status. Epidemiological studies are particularly valuable in understanding complex relationships between food intake (dietary exposure) and determinants of diseases with multiple etiologies and long latent periods. Examples of such studies include the relationships between low folic acid intake and increased incidence of spina bifida, and elevated saturated fat intake and elevated risk of arteriosclerosis. There are, however, limitations to these studies in that they describe relationships rather than prove cause and effect. Frequently, clinical trials and intervention studies are used as follow-up studies to evaluate more fully the questions raised by epidemiological evidence.
Nutrition in Clinical Practice
Scientific evidence continues to mount regarding the key roles that nutrients and their metabolism play in the prevention of the most common chronic diseases. Half of the leading causes of death in the United States (heart disease, cancer, stroke, and diabetes) are associated strongly with unhealthy eating habits. Clinical nutrition is the practice of applying research evidence to aid in the care of individuals with or at risk for diet-related diseases. These principles are used to develop individualized nutrition care plans. Generally, diseases may affect nutritional status by (a) decreasing the intake of nutrients, (b) altering the metabolism of nutrients (or unusual losses), or (c) altering energy expenditure. Alternatively, as mentioned briefly above, poor nutritional status can lead to disease. For example, zinc deficiency can decrease the function of the immune system that in turn leads to increased risk for diarrhea and infectious diseases.
Assessment of nutritional status is essential for identifying undernourished and overnourished states (obesity is now a major health problem) and estimating the optimum intake to promote normal growth and well-being. Nutritional assessment has several components, including the evaluation of dietary intake, growth status, body composition, energy expenditure, and biochemical measures of nutritional status in the context of a medical history, diagnoses, and current therapy. These data are used to develop individualized nutritional care plans, which may include recommendations for total energy intake, adjustments in the diet to increase or decrease the consumption of certain foods, and possibly the inclusion of nutrient supplements. For patients who cannot be fed orally, more technology-based nutritional support is used to maintain or improve nutrient intakes and nutritional status. This involves either feeding the patient through a tube directly into the stomach or intestine (enteral) or through an intravenous line directly into the bloodstream (parenteral). Because malnutrition will add to complications of illness and prolong the illnesses and hospitalization, appropriate assessment of the patient is extremely important. In the complex and rapidly changing context of critical illness, individualized nutrition assessments are crucial and require the sequential monitoring of all patients to maintain appropriate nutritional care plans.
It is unlikely that individuals who have not been seriously ill have had the opportunity to seek the counsel of a trained nutritional professional for developing an individualized diet plan. The average American displays a keen interest in how nutrition affects his or her health, and is disappointed with the information physicians are able to provide because traditional medical training has limited nutrition content. Therefore, greater numbers of individuals are seeking nutrition information for themselves, and using the information to self-diagnose and self-prescribe. The advances in communications technology, particularly the explosion of information on the World Wide Web, allow the ready accessibility of sound nutritional advice, and substantial amounts of quackery. Without training and a significant amount of time dedicated to the task, it is difficult to decipher truth from fraud. Future directions in nutritional education likely will include tools to aid Americans in deciphering information, particularly from the Internet, in order to make educated choices to optimize their diets and live healthier lives (see Table 2).
Nutrition in Public Policy: Monitoring and Education
Nutrition in public health or nutrition policy generally is regarded as the combined efforts taken toward improving
|Credible sources of nutrition information on the World Wide Web|
|American Dietetic Association: www.eatright.org|
|American Society for Clinical Nutrition: www.faseb.org/ascn|
|Society for Nutrition Education: www.sne.org|
|American College of Sports Medicine: www.acsm.org|
|Institute of Food Technologists: www.ift.org|
|Centers for Disease Control: www.cdc.org|
|Office of Food Labeling:|
|Center of Food Safety and Applied Nutrition:|
|Food and Nutrition Information Center: www.nal.usda.gov/fnic|
|Center for Nutrition Policy and Promotion: www.usda.gov/fcs/cnpp.htm|
|International Food Information Council:|
|National Center for Complementary and Alternative Medicine:|
|Office of Dietary Supplements of NIH: http://odp.od.nih.gov/ods/|
|Quack Watch: http://www.quackwatch.com/|
|Gatorade Sports Science Institute: www.gssiweb.com|
|National Dairy Council: www.dairyinfo.com|
|The Dannon Company: www.dannon.com|
|United Fresh Fruit and Vegetable Association: www.uffva.org|
nutrition and health status of populations. With increasing emphasis on health promotion and disease prevention, there is a proliferation of nutrition-related disease prevention, screening, and education programs targeted at increasing fiber, fruit, and vegetable intake, and reducing saturated fat intake. Additionally, a number of food assistance programs and mandated food fortification programs have been instituted, all promoting a healthy diet and lifestyle.
Nutrition research, public policy programs, and nutrition surveillance systems work synergistically like spokes on a wheel. Evidence obtained from scientific research is used to set nutritional recommendations such as the Dietary Reference Intakes and the Dietary Guidelines for Americans. These standards are used to judge the adequacy of the American diet, provide the basis for nutrition labeling of foods, formulate special diets, and guide the development of food fortification and nutrition policy developed to assist those who are at nutritional risk. Specific food assistance programs (such as, food stamps, Special Supplementary Nutrition Program for Women, Infants, and Children) are targeted at specific economically disadvantaged and nutritionally at-risk populations. Fortification programs generally are less specific, but some target at-risk populations through specific foods, for example, vitamin Dortified milk to prevent rickets in young children. Finally, the wheel is completed by nutrition monitoring programs that are used to evaluate the effectiveness of instituted policies. The National Health and Nutrition Examination Survey (NHANES) and the Continuing Survey of Food Intake of Individuals (CSFII) are ongoing monitoring tools used to assess the population's nutrient intakes, nutrition and health status, and knowledge and attitudes about health.
Perhaps most important, public health nutrition includes the dissemination of scientific findings, the explanation of dietary recommendations, and outreach of federal assistance programs. The responsibility of communicating experimental findings in an understandable form falls on nutrition scientists, journalists, educators, and the public. The scientists are responsible for interpreting the research findings into a form that is understandable to the general public. Journalists are responsible for communicating the scientific message in an objective way, and the public is responsible for pursuing an accurate understanding of the issues. Various government agencies have the responsibility to organize and administrate the myriad of nutritional policies and programs, and to communicate information regarding these programs to the public.
The Future of Nutrition and Food Science
In the twentieth century nutrition research, practice, and public policy shifted from a focus on the quantitative aspectso ensure food security and eradicate nutritional deficiencieso a greater attention on the qualitative aspectso achieve optimal, balanced, dietary intakes. In the twenty-first century nutrition research, practice, and policy will likely explore the following areas:
relationships between human genetics and nutrition, the role of genetically modified foods in human health,
the relationship of nonfood substances in the promotion of health and the bioengineering of functional foods,
the promotion of economic growth and food security in developing nations to prevent or delay the undesirable health effects of malnutrition, and
the prevention and treatment of the obesity epidemic in children and adults.
Relationships between food intake and human health will continue to be of great public interest, and nutrition and food scientists will face new challenges in a fasterchanging environment.
See also Assessment of Nutritional Status; Dietary Assessment; Dietary Guidelines; Dietary Systems: A Historical Perspective; Dietetics; Enteral and Parenteral Nutrition; Food Stamps; Functional Foods; Malnutrition; Nutrients; Nutritionists; Nutrition Transition: Worldwide Diet Change; Obesity; Physical Activity and Nutrition; Vitamins; WIC (Women, Infants, and Children's) Program.
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Ellen B. Fung Virginia A. Stallings