Diet therapies are specially designed and prescribed for medical and/or general nutritional reasons.
Purpose
Diet therapy promotes a balanced selection of foods vital for good health. By combining foods appropriate for each individual and drinking the proper amount of water, one can help maintain the best possible health. Eating the proper diet is critical for the health of individuals, groups with special medical and dietary needs, and entire populations afflicted with malnutrition.
Precautions
A particular modified diet is prescribed specifically for each individual. Those individuals who have medical conditions or who are sensitive to certain foods need to be very compliant and cautious about what they eat.
Individuals should not follow a "fad" diet without first consulting a registered dietitian or physician. Popular (but sometimes dangerous) low-carbohydrate diets, for example, may deprive the body of the glucose it needs for central nervous system and brain functions.
Description
Nutrition is the science concerned with the human body's use of nutrients and food substances. Proper nutrition decisions are important for the optimal health of each individual. This is especially true for those individuals with specific dietary needs and acute or chronic diseases. The nutrients necessary to maintain normal growth and health include proteins, carbohydrates, fats, vitamins, and minerals. Included in these nutrients are eight amino acids the body cannot produce but that must be derived from proteins, four fat-soluble and ten water-soluble vitamins, ten minerals, and three electrolytes.
Nutrient classes
PROTEIN. Protein is important for building body tissue and synthesizing enzymes. Enzymes are specialized organic substances that act to regulate the speed of chemical reactions in human metabolism. Twenty amino acids of the 100 or more occurring in nature make up proteins. Animals and plants are quick and available sources of what are termed "essential" amino acids; they are called essential because the body cannot build them internally. Normal growth and health are dependent upon these essential amino acids. Dietitians recommend that a healthy diet includes 10–20% of daily calories from protein (poultry, fish, dairy, and vegetable sources).
CARBOHYDRATES. Carbohydrates provide most of the energy in the majority of human diets. Foods rich in carbohydrates are usually the most abundant and cheapest. The carbohydrates containing the most nutrients are the complex carbohydrates, such as unrefined grains, tubers, vegetables, and fruits. Simple carbohydrates or sugars should be eaten in moderation, since they are high in calories but low in nutrients.
Carbohydrates are needed in the form of glucose by the brain and central nervous system (CNS). A minimum of 1.6 oz (50 g) of glucose is required daily for proper functioning of the CNS. If the body is denied carbohydrates, it will use ketone bodies for energy, but this is not a good energy source for the body, and may have unfavorable health effects.
FATS. Fats supply energy and essential fatty acids and promote absorption of the fat-soluble vitamins A, D, E, and K. The accumulation of body fat has become a serious health concern; over 50% of Americans are considered overweight. Fats are compact fuels efficiently stored in the body for later use when carbohydrates are in short supply. Fats produce more than twice as much energy as carbohydrates, approximately 9 Kcals/gram versus about 4 Kcals/gram for carbohydrate and protein. Dietary fats are broken down into fatty acids that pass into the blood. These fatty acids are either saturated or unsaturated (mono-unsaturated, polyunsaturated, or trans-unsaturated). Saturated fats, derived mostly from animal sources, have been found to raise the level of total cholesterol in the bloodstream, and certain unsaturated fats tend to lower the level of total cholesterol in the blood stream. For example, mono-unsaturated fats like oleic acid in olive oil reduce low-density lipoprotein cholesterol (bad cholesterol) and increase high-density lipoprotein cholesterol (good cholesterol), thus reducing the risk of heart disease. Saturated and trans-unsaturated fatty acids both raise serum cholesterol; in contrast, neither mono-unsaturated nor polyunsaturated fats have this effect.
INORGANIC MINERAL NUTRIENTS. Inorganic mineral nutrients are required to build tissues. They are also important for muscle contractions, nerve reactions, and blood clotting. All of these mineral nutrients must be supplied in the diet. Minerals are categorized as major elements or trace elements. Major elements consist of calcium, phosphorus, magnesium, iron, iodine, and potassium. Trace elements include copper, cobalt, manganese, fluorine, and zinc.
VITAMINS. Vitamins increase the breakdown and absorption of proteins, carbohydrates, and fats. Certain vitamins help form blood cells, hormones, nervous system chemicals, and genetic materials. Vitamins are classified into two groups: fat-soluble vitamins, such as A, D, E, and K; and water-soluble vitamins, such as vitamin C and the B-vitamin complex. Fat-soluble vitamins are usually found in foods that contain fat. Because excess amounts are stored in the body's fat and in the liver and kidneys, fat-soluble vitamins do not have to be consumed every day. The water-soluble vitamins, C and B complex, cannot be stored and must be consumed daily to replenish the body's supply.
Food types
Foods can be widely grouped into breads and cereals; legumes, tubers or starchy roots; vegetables and fruits; meat, fish, and eggs; milk and milk products; fats and oils; and sugars. Breads and cereals are high in starches (carbohydrates), but whole cereals also often supply significant amounts of protein. However, these cereals should be eaten in conjunction with other protein foods to supply all the essential amino acids. Meat, fish, and eggs supply all the essential amino acids that the body needs to build its own proteins.
Milk and milk products also provide a plentiful amount of protein, phosphorus, calcium, and vitamins. Legumes are rich in starch but also furnish more protein than cereals or tubers. Tubers provide a variety of minerals and vitamins. Vegetables and fruits are a direct source of many minerals and vitamins. Fats and oils are high in calories but usually contain few nutrients. Sugars, which are heavily consumed in more affluent countries, contain few nutrients and can cause tooth decay.
Dietary guidelines
The Food and Nutrition Board of the National Research Council of the National Academy of Sciences has determined dietary standards called Recommended Dietary Allowances (RDA). These standards explain the daily amounts of energy, protein, minerals, and fat-soluble and water-soluble vitamins needed by healthy males and females, from infancy to old age. The RDA has been under revision and is replaced by the Dietary Reference Intakes (DRI) as of 2001. The DRI will be applicable to Canadians and Americans. Like the RDA, the DRI recommends an average daily intake for a nutrient, but the DRI is more comprehensive than the RDA. It incorporates updated scientific research into providing expert guidance for issues such as risk reduction for chronic disease and upper limits of intake for nutrients with adverse health effects.
Experts in nutrition recommend a variety of foods and the maintenance of an ideal weight. Large amounts of fat, saturated fat, and cholesterol should be avoided. Individuals should consume adequate starch and fiber and avoid excess sugar and sodium.
If you drink alcohol, do so in moderation; no more than 2 drinks per day of wine, beer, or spirits.
The food pyramid, developed by nutritionists, provides a visual guide to healthy eating. At its base are those foods that should be eaten numerous times each day, while at its apex are those foods that should be used sparingly. The pyramid suggests a range of servings in each group so that the number of servings can be adjusted to suit each individual's caloric requirements. The daily recommendations (from bottom to top) of the food pyramid include:
bread, cereal, rice, and pasta: 6–11 servings
vegetables: 3–5 servings
fruits: 2–4 servings
milk, yogurt, and cheese: 2–3 servings
meat, poultry, fish, dried beans, eggs, and nuts: 2–3 servings
fats, oils, and sweets: use sparingly
Energy requirements
Carbohydrates, proteins, and fats provide energy in the form of calories to fuel the body for metabolic processes, growth, and activity. When an individual consumes as many calories each day as the body uses, they are in a state of energy balance and will neither gain nor lose weight. When more calories are eaten than the body uses, the excess calories are stored as fat and weight increases. On the other hand, when fewer calories are consumed than the body needs, stored fat is burned and weight decreases. Using the metric system nomenclature, a kilojoule (kJ) is used instead of a kilocalorie (kcal), where 1 kcal=4.184 kJ and 1 megajoule (MJ)=1000 kJ.
The amount of energy required depends on such factors as an individual's weight, gender, age, and activity level, so an estimation should be made based on these parameters. Some dietary guidelines do suggest an average energy intake for people in different age groups, but many of the guidelines do not base the estimations on measures such as activity level. The Food and Agriculture Organization/World Health Organization uses a more accurate method for estimating energy requirements for populations and individuals. They define energy requirement as "... the amount of energy needed to maintain health, growth, and an appropriate level of physical activity." The "appropriate level of physical activity" is not a standardized level, but is dependent on social, cultural, and lifestyle factors. Physical activity categories for light, moderate activity or heavy work are used to provide a better energy estimation. For example, a 143 lb (65 kg) woman between the ages of 30-60 years who participates in light activity would require about 2190 kcal/day (9.2 MJ/day). At a moderate activity level, this same woman would require approximately 2300 kcal/day (9.6 MJ/day) and 2550 kcal/day (10.7 MJ/day) for heavy activity.
Calorie-modified diet
Calorie-modified diets are prescribed to correct weight problems with a healthy diet. Low-calorie diets are designed for weight reduction and are prescribed for people who are overweight or obese. High-calorie diets are recommended for people with greatly increased energy needs such as athletes in training or individuals fighting diseases such as cancer, AIDS, or cystic fibrosis. High-calorie diets are also prescribed to treat anorexia nervosa.
Calorie-modified diets are planned by dietitians and should be prescribed following a complete physical examination and dietary assessment or dietary history. A low-calorie diet provides enough energy to meet the person's metabolic needs and activity level. It includes a balanced variety of foods, but limits carbohydrates and alcohol. A low-calorie diet should not aim to promote a weight loss of more than approximately 1–2 lb (500 grams to one kilogram) per week. In general, for a slightly overweight person, it is not wise to lose more than 1 lb (about 500 grams) per week. A high-calorie diet usually provides an extra 500–1,000 calories, leading to a weight gain of about 1 lb (500 grams) per week for most people. It has a high protein content, normal fat content, and emphasizes foods that pack many calories into a small volume. Snacking between meals is encouraged as a way to increase the calories consumed.
When caloric limits allow, have no more than two drinks of wine, beer or liquor per day.
Fiber-modified diet
Fruits and vegetables are excellent sources of fiber. Fiber has important nutritional benefits such as facilitating the movement of food through the digestive tract, helping to prevent constipation. Research suggests low dietary fiber may be responsible for increasing the incidence of diverticulosis and may also be associated with cancer of the colon.
High-fiber diets, including whole grains (especially bran), raw vegetables, unpeeled fresh fruits, nuts, and seeds, are recommended to:
assist with weight loss in people who are overweight and improve sugar tolerance in diabetics
Low-fiber diets exclude raw fruits and vegetables, whole grains, nuts, and seeds, while emphasizing soft, mild foods. They are recommended to:
decrease fecal bulk
slow intestinal movement
decrease stomach acid secretion
treat a variety of disorders including indigestion, diarrhea, bowel inflammation, and heart attack
Protein-modified diet
High-protein diets are designed to provide about 0.05 oz (1.5 g) of protein for each kilogram of a person's body weight. Complex proteins, such as milk and meats, should make up one-half to two-thirds of the daily protein requirement. High-protein diets are recommended for people who:
have an increased need for protein due to protein-calorie malnutrition, severe stress, or conditions such as AIDS, cancer, or burns with high metabolic rates that lead to the loss of large amounts of protein
A low-protein diet excludes dairy products and meats, and requires that about three-fourths of the daily allowance of protein come from high-value protein sources. Supplements may be prescribed to prevent amino acid deficiencies. Low-protein diets are used in treatment of cirrhosis and kidney disease.
Low-cholesterol diet
Dietary modification is the first weapon in the fight against the high cholesterol levels that contribute to heart disease and atherosclerosis. Low-cholesterol diets are prescribed to reduce the risk of heart disease and to treat atherosclerosis, diabetes, high cholesterol (which may be hereditary and might also require cholesterol-reducing drugs), and high blood pressure. A low-cholesterol diet is not a cure for the conditions it is prescribed to treat, so most people must stay on the diet for the rest of their lives.
The American Heart Association eating plan recommends that total cholesterol intake should be less than 0.01 oz (300 mg) per day and total fat intake should be 30% or less of total calories. Saturated fatty acid intake should be less than 10% of calories or for anyone with elevated blood cholesterol levels or heart disease, saturated fat and cholesterol intake is limited even further to 7% of total calories per day.
Polyunsaturated fatty acid intake should be 8–10% of calories.
Mono-unsaturated fatty acids should make up the rest of the total fat intake, up to 15% of total calories.
These guidelines apply to all healthy individuals over two years of age.
Low-fat diet
Most American diets contain too much fat. Fat often makes up about 40% of total calories consumed each day. Registered dieticians recommend limiting fat to 30% or less of daily calories, since consumption of too much fat has been linked to obesity, heart disease, and several types of cancer. A low-fat diet usually limits daily fat intake to 1.76 oz (50 g), while an extremely low-fat diet limits fat consumed each day to 0.88–1.05 oz (25–30 g). The grams of fat in your diet will depend on the calories you need. Low-fat diets are recommended to:
Some fat is required in the diet to prevent essential fatty acid deficiencies, but most people consume more than enough fat to meet these needs.
Cutting back on fat will likely help you eat fewer calories. Make sure to read the nutrition facts label on foods. The Dietary Guidelines recommend limiting fat intake to 30% of calories or less, which corresponds to1.87 oz (53 g) of fat in a 1,600 kcal diet, 2.57 oz (73 g) of fat in a 2,200 kcal diet, and 3.28 oz (93 g) of fat in a 2,800 kcal diet.
Gluten-free diet
Gluten and gliadin are proteins found in certain grains and grain-containing products. These proteins are toxic to cells within the intestinal tract of an individual who is "intolerant" and cause difficulty in food absorption. Celiac disease is caused by intolerance to these proteins. This intolerance causes patients with celiac disease to suffer weight loss, diarrhea, malnutrition, and bloating. By eliminating foods containing gluten from the diet, further damage to the intestines can be prevented, symptoms are relieved, and malabsorption of nutrients is corrected. A gluten-free diet eliminates all foods containing wheat, rye, barley, and malt, and must be followed for life.
Low-purine diet
This diet restricts food, such as sardines, liver, and eggs, that cause the body to produce uric acid. It is usually prescribed as part of a treatment program for gout (a disease usually caused by having too much uric acid in the body) and kidney stones, which also includes exercise and medication. In addition to excluding organ meats (sweetbreads, liver, kidney) and certain types of fish (anchovies, sardines, mackerel) and limiting the amount of other purine-containing foods such as shrimp, meats, and dairy products, this diet emphasizes drinking about 2 qt (1.89 l) of water and fruit juice daily, to promote the excretion of uric acid, and eating fruits and vegetables that increase urine alkalinity and the solubility of uric acid.
Low-salt diet
On the average, Americans consume about 0.17 oz (5 g) of salt or sodium daily. Dietary guidelines suggest that 0.08 oz (2.4 g) of sodium should be the upper limit, even if there are no signs of heart disease. Most people with heart disease should limit their sodium intake to less than 0.07 oz (2 g) a day, and some low-salt diets restrict sodium to as little as 0.008 oz (250 mg) per day. The amount of salt in the diet is important for people who have high blood pressure or congestive heart failure.
Some experts believe excessive intake of salt is a major reason for high blood pressure, especially in Western countries. Excess sodium encourages the body to retain fluid, thereby increasing fluid pumped by the heart and circulating in the bloodstream. Diets high in salt also can be harmful to people with congestive heart failure because the excess fluid backs up into the lungs, causing congestion.
Potassium chloride is a common ingredient in salt substitutes. But too much potassium can be harmful for people with kidney problems. One way to enhance the flavor of food while eliminating salt is to add lemon juice, herbs, spices, or flavored vinegar.
Low phenylalanine diet
A low phenylalanine diet is normal treatment for phenylketonuria (PKU). PKU is a rare genetic disorder in the degradation of dietary phenylalanine that if left untreated, can result in severe progressive mental retardation. The diet is extremely restrictive, and rigorous dietary compliance is necessary to reduce or prevent mental retardation. Close supervision by a registered dietitian or physician is necessary.
A normal diet cannot be tolerated by people with PKU. Dietary treatment necessitates avoiding foods containing high levels of protein. A diet contains only the amount of phenylalanine which is essential for the body. Basic principles of the PKU diet state that:
Meat, fish, cheese, eggs, milk and nuts are not allowed because they are rich in protein and thus phenylalanine.
Other foods which contain moderate amounts of protein (i.e. potato and cereals) are given in small measured quantities. These foods are spread out between the day's meals to keep the phenylalanine levels steady.
Most fruits, some vegetables, and salads can be taken in normal quantities but excessive use should be avoided.
Sugar, jam, syrups, and fats such as butter, lard, and cooking oil can be used fairly freely.
There are many low protein manufactured foods available on prescription. These can all be taken freely to provide variety in the diet. Foods include pasta, low protein bread, biscuits, flour, and spaghetti, etc.
Infants can be fed phenylalanine-free formulas.
There is a high incidence of tooth decay among individuals affected by PKU because of the increased amounts of CHOs consumed.
Diabetic diet
For the most part, dietary management is the key to keeping diabetes in check. There is controversy regarding dietary recommendations for diabetes control and at present, there is no single diet that meets the needs of all diabetics. The general rules for healthy eating as discussed previously apply to diabetics as well.
Several dietary methods are available for controlling blood sugar levels. The Food Guide Pyramid is recommended by the U.S. government for everyone including diabetics. Some experts believe these dietary guidelines may be sufficient for diabetics, although there are more detailed dietary methods available for controlling blood sugar. These methods may be complex, however, which deters many diabetics from using them. The American Diabetic Association and American Dietetic Association developed the Diabetic Exchange Lists, the most common system used for controlling blood sugar. Other nutrition experts recommend adopting a Mediterranean diet because they point out the food pyramid has some drawbacks; for example, there is little focus on meal planning. Carbohydrate counting plans may assist but may also be complicated and require a committed learner; the concepts of the Diabetic Exchange Lists may be difficult to understand for some people.
Type 1 and type 2 diabetics on insulin or oral medication must focus on controlling blood glucose levels by coordinating food intake with insulin administration or medication, or other variables such as exercise.
Quickly respond to hyperglycemia (high blood sugar).
Maintain consistent snacking habits.
The recommendation given by the American Diabetes Association is to eat more starches. This is the opposite of what has been advised in past years. Current research studies now show it is healthiest for everyone to eat more grains, beans, and starchy vegetables to control fat and cholesterol. Total carbohydrate intake has greater impact on blood glucose control than the source of carbohydrate. However, consumption of complex carbohydrates (i.e. whole grain bread, beans, etc.) are better than eating foods that are sucrose (simple sugar) based.
Both weight loss and blood sugar control are particularly important for overweight type 2 diabetics who are not taking medication. Health effects are most beneficial after initial weight loss. A 10% decrease in body weight can control the progression of type 2 diabetes. Other important issues are controlling lipid (cholesterol and triglyceride) levels, and blood pressure. Controlling fat intake is important because diabetics are about twice as likely to get cardiovascular disease compared to other people.
Research shows that diabetics have the same protein requirements as other people, but with onset of nephropathy, protein should be limited to 0.8 grams/kg per day for adults, with 80% coming from high biological value protein.
Traditional diets may offer some health advantages
Certain populations have dietary habits that are much healthier than the typical Western diet, which is often too high in fat and cholesterol. Research has shown that the traditional Mediterranean diet, Japanese diet, or "hunter-gatherer" diets have health advantages. The dietary habits characteristic of Mediterranean countries with the consumption of olive oil (mono-unsaturated fatty acid) as the main fat source appear to provide optimal health benefits with a low incidence of coronary heart disease. The Mediterranean diet consists of large amounts fruit, vegetables, pulses, nuts, cereal products, and fish, while generally only small amounts of meat and dairy foods are consumed.
Preparation
Effective estimation of an individual's diet is required in order to provide dietary counseling and guidance. If a dietary assessment is not conducted in preparation, using proper methodologies, it will be difficult for the dietitian to draw any conclusions regarding the need for diet therapy.
Despite the diet type, all foods should be prepared appropriately. This includes adequate cooking time and proper storage. Some diets must be phased-in gradually.
Aftercare
Regular physician follow-up is always important when the individual has been placed on a special diet because of a health condition.
One cannot live on "a diet" permanently, because strict guidelines are difficult and painstaking to follow. Therefore, dietary modifications have to be lifestyle
KEY TERMS
Calorie—Commonly referred to as a calorie, but is actually a kilocalorie (kcal). A kilocalorie is the energy required to raise the temperature of one kilogram of water one degree Celsius. It is how the energy content of food is measured.
Dietary assessment—An estimation of food and nutrients eaten over a particular time point. Some of the most common dietary assessment methods are food records, dietary recalls, food frequency questionnaires, and diet histories.
Dietitian—A dietitian is a health professional who has a bachelor's degree, specializing in foods and nutrition, and in addition undergoes a period of practical training in a hospital or community setting. Many dietitians further their knowledge by pursuing master's or doctoral degrees. The title "dietitian" is protected by law so that only qualified practitioners who have met education qualifications can use that title.
Electrolytes—Any of the various ions, such as sodium, potassium, or chloride, required by cells to regulate the electric charge and flow of water molecules across the cell membrane.
Kilojoule—In Europe and other countries, food energy values are frequently given in kilojoules (kJ), the metric unit of energy. Using the metric system nomenclature, a calorie is converted into a kilojoule (kJ), where 1 kcal=4.184 kJ and 1 megajoule (MJ)=1000 kJ. To convert kilojoules to kcals, divide by 4.184.
Legumes—A pod, such as a pea or bean, that splits into two valves with the seeds attached to one edge of the valves.
Nutritionist—Some dietitians call themselves "nutritionists" but in general, the term "nutritionist" is not protected by law, therefore anyone can call themselves a nutritionist.
Trans-unsaturated fatty acids (also called transfatty acids or trans-fat)—To make foods that will stay fresh on the shelf or to get a solid fat product, such as margarine, food manufacturers hydrogenate (i.e. add hydrogen) to polyunsaturated oils. This changes the double bond on the carbon atom from a cis configuration to a trans configuration, making the fatty acid saturated, and more of a health concern. For example, stick margarines are known to contain more trans fatty acids than liquid oils.
changes in food selection and more healthy attitudes about nutrition and wellness.
Risks
There is always the possible risk of non-compliance of any diet. However, when the individual is placed on the appropriate diet and the primary physician is aware of any known allergies, there are very few risks involved, if any.
Results
When special diets are followed as prescribed, better health is the expected outcome, with a decreased risk of acquiring many diseases. However, it is up to an individual to implement the necessary dietary modifications. If a patient does not follow the recommended dietary guidance, then they will not receive a benefit. Typically, modest effects are seen in weight loss or reduction in serum lipids (i.e. cholesterol) often due to failure to fully comply with the dietary recommendations provided by a dietitian or doctor.
The outcome of any diet therapy will be better when combined with exercise unless the patient is unable to exercise for medical reasons.
If the appropriate diet is prescribed by medical professionals, abnormal results are very rare.
Health care team roles
A certified nutrition professional such as a registered dietician (R.D.) should be seen for a dietary assessment and professional dietary counseling prior to commencing diet therapy. Beware of individuals prescribing diets without an education in dietetics and nutrition. In general, only registered dietitians have sufficient training and knowledge to accurately assess the nutritional adequacy of a patient's diet, especially if chronic disease is present. Some dietitians call themselves nutritionists, but the term "nutritionist" is not regulated by law; therefore anyone can call themselves a nutritionist. A doctor may also have a nutrition background or specialization and may thus be able to conduct a dietary assessment or to provide general nutrition advice and/or diet therapy.
BOOKS
Institute of Medicine, ed. Dietary Reference Intakes: Risk Assessment (Compass Series). Washington, D.C.: National Academy Press, 1999.
Institute of Medicine. Dietary Reference Intakes: Applications in Dietary Assessment. Washington, D.C.: National Academy Press, 2001.
Larson-Duyff, Roberta. The American Dietetic Association's Complete Food & Nutrition Guide. New York: John Wiley & Sons, 1998.
Mahan, L. Kathleen, and Sylvia Escott-Stump, eds. Krause's Food, Nutrition, & Diet Therapy. London: W.B. Saunders Co, 2000.
Netzer, Corinne T. The Complete Book of Food Counts. New York: Dell Publishing Company, 2000.
Rodwell-Williams, Sue. Essentials of Nutrition and Diet Therapy (With CD-ROM for Windows and Macintosh). London: Mosby-Year Book, 1999.
PERIODICALS
Hu F.B., et al. "Trends in the incidence of coronary heart disease and changes in diet and lifestyle in women." New England Journal of Medicine 343 (2000): 530–537.
Stampfer, M. J., et al. "Primary prevention of coronary heart disease in women through diet and lifestyle." New England Journal of Medicine 343 (2000): 16–22.
ORGANIZATIONS
American Dietetic Association. 216 W. Jackson Blvd.
Sign up with Facebook
