I 356 iatrogenic malnutrition See HOSPITAL-INDUCED MALNUTRITION . IBD See INFLAMMATORY BOWEL DISEASE . IBS See IRRITABLE BOWEL SYNDROME. iceberg lettuce See LETTUCE. ice cream A frozen DESSERT containing flavored, sweetened frozen cream and MILK products, and SUGAR. Frozen desserts based on EGGS, cream, and milk were apparently invented in the 1600s, although frozen blends of fruits were served in ancient China, where salt mixtures were used to lower the temperature below freezing. Americans eat an average of 15 quarts a year per person. Ice cream is a high- CALORIE , high-FAT, and high- sugar food. Unless it is homemade, ice cream will usually contain artificial coloring, flavorings, and stabilizers such as LOCUST BEAN GUM, GUAR GUM, CARRAGEENAN, GELATIN, and alginic acid or cellulose derivatives. Federal law requires that ice cream contain at least 10 percent fat ( BUTTERFAT), and most regular ice creams provide 10 percent to 12 percent butterfat. Super-premium vanilla ice cream contains 16 percent to 20 percent butterfat. In con- trast, ice milk contains 2 percent to 7 percent fat, while sherbet contains 1 percent to 2 percent fat. Ice cream usually contains sugar or other sweeten- ers and emulsifiers like POLYSORBATES and MONO- GLYCERIDES stabilize ice cream during processing. Nondairy frozen desserts resembling ice cream have no legally defined butterfat content, and although they are low-fat options, sometimes these desserts have more total calories per serving than traditional ice cream due to their high sweetener content. One cup of rich vanilla-flavored ice cream with about 16 percent fat provides: 349 calories; protein, 4.1 g; carbohydrate, 32 g; fat 23.7 g; cholesterol, 88 mg; calcium 151 mg; vitamin A, 219 retinol equiv- alents; thiamin, 0.04 mg; riboflavin, 0.28 mg; niacin, 0.12 mg. One cup of regular vanilla ice cream with about 11 percent fat provides: 269 calories; protein, 4.8 g; carbohydrate, 31.7 g; fat, 14.3 g; cholesterol, 59 mg; calcium, 176 mg; vitamin A, 133 retinol equiv- alents; and similar amounts of thiamin, riboflavin, and niacin to those found in rich vanilla ice cream. One cup of vanilla-flavored ice milk with about 4 percent fat provides: 184 calories; protein, 5.2 g; carbohydrate, 29 g; fat, 5.6 g; cholesterol, 18 mg; calcium, 176 mg; vitamin A, 52 retinol equivalents; and similar amounts of other vitamins. (See also DAIRY -FREE FROZEN DESSERTS; DIETARY GUIDELINES FOR AMERICANS .) ideal body weight An outmoded standard for body weight that originated from data collected by U.S. life insurance companies from their policy holders who lived the longest. Ideal body weight was listed as the average weight for a given age, height, body, or “frame” size. From these data grew the classic definition for OBESITY as a weight 20 percent greater than the ideal body weight. Part of the problem with this standard of ideal body weight lies in the nature of HEIGHT-WEIGHT TABLES. Weight charts and tables do not take into account individual variations in body structure (muscles and bone mass); consequently, there is no stan- dard for measuring small, medium, or large body frames. There is no single ideal body weight for a group of people because every person has an individual, desirable weight. Selecting a realistic body weight as a goal has proven to be far more useful than striving for a rigidly defined standard. A realistic body weight is one that can be readily maintained without intermittent DIETING. A measure of body FAT is more useful than total body weight because body weight may not corre- late with the amount of fat on a lean person. Fur- thermore, ideal body weight provides no indication of fat distribution. Some fat deposits are riskier for heart disease than others. Methods of accurately measuring body fat at clinics include buoyancy testing with underwater weighing (requiring a spe- cial tank) and SKIN FOLD thickness measured by skin calipers or by skin resistance measurements. Suggestions for estimating an optimal body weight include: For males, take 106 pounds for the first 5 ft. of height, then add six pounds for each additional inch of height. For females, take 100 pounds for the first 5 ft., then add five pounds for each additional inch. (See also BODY MASS INDEX; FAT-FOLD TEST.) idiopathic A medical term that is applied to a disease or condition arising spontaneously from an unknown cause. Idiopathic GOUT and high blood pressure are examples. ileitis See CROHN’ S DISEASE. ileum The last three-fifths of the small INTESTINE that joins the large intestine (COLON). The length of the ileum varies among individuals, ranging from 15 to 30 ft. in adult men. The ileum absorbs FAT, fat-soluble vitamins, CALCIUM, MAGNESIUM, VITAMIN B 12 , and AMINO ACIDS. BILE salts, which act as the detergents in bile required for fat DIGESTION,are also absorbed in the ileum and are recycled by the liver to released once again in bile. Flow of material between the ileum and colon is regulated by the ileocecal valve. (See also ENTERO- HEPATIC CIRCULATION.) illness Ill health or disease; the opposite of well- ness. Illness reflects imbalanced body functions and can thus be regarded as a change away from the healthy state, in which all systems function within normal limits ( HOMEOSTASIS). An illness may be localized, in which a limited region of the body is affected, or it may be systemic, in which several parts of the body or the whole body are affected. Pain is often associated with illness, although pain is not equivalent to disease. Pain gen- erally indicates that an imbalance exists in the body. The imbalance could reflect an unhealthy lifestyle, such as dietary excess or deficiency, or it could be associated with infection and inflammation. Most illnesses are self-limiting, meaning that the body generally can cure itself when given the oppor- tunity. It is now clear that the body’s systems work together to maintain health. Particularly important are the IMMUNE SYSTEM, the NERVOUS SYSTEM, and the ENDOCRINE SYSTEM (hormone-producing system). An imbalanced immune system affects the brain, and the brain alters immunity and hormone pro- duction. Hormones in turn affect nerve function. As an example, perceived STRESS can trigger a FIGHT OR FLIGHT RESPONSE by the brain. The stress response is modified by hormones, and sustained, elevated adrenal hormones due to prolonged stress affect the immune system and decrease the immune response to foreign invaders. Whether or not an individual becomes ill depends on a complex interplay of many factors, broadly categorized according to medical history and environmental influences. Family history reflects patterns of inheritance, over which one has no control. Genetic predisposition thus increases the risk of many chronic, degenerative diseases of AGING, such as OSTEOPOROSIS, heart disease and STROKE , high blood pressure, and DIABETES. Health history can have a profound effect on susceptibility to illness. Thus, prior injury, deficiency, or illness can set the stage for a subsequent illness. For example, arthritis can begin at the site of a former injury, and prolonged treatment with a broad-spec- trum antibiotic can destroy beneficial gut bacteria and promote a yeast infection. Prior drug treatment can alter the body’s ability to destroy alcohol, and pretreatment with alcohol can alter the body’s abil- ity to degrade many drugs. In terms of public health, immunization against polio, flu, or tetanus reduces the risk of these diseases. At the beginning of the 20th century, niacin deficiency caused wide- spread pellagra and associated mental illness in the South. The enrichment of bread and grain products with the B vitamin NIACIN in the 1920s essentially eliminated pellagra as a public health issue in the United States. illness 357 Due to differences in inheritance and environ- ment, toxic exposure, nutritional status, and med- ical history, each person is biochemically unique. Thus, individuals vary in their ability to protect themselves against damaging effects of FREE RADI- CALS, and to detoxify potentially dangerous chemi- cals that they eat or drink or breathe at home or in the workplace. Although neither a family history nor a medical history can be altered, lifestyle choices can pro- foundly impact susceptibility to illness. The most frequently cited RISK factors for illness and prema- ture death include the use of tobacco and alcohol, accidental injury, unwanted pregnancy, drug abuse, and inadequate nutrition. The growing awareness that prevention is the most cost-effec- tive and permanent solution to many health issues has lead many physicians to work with their patients as partners in health to empower them in making healthful choices for themselves and their families. This approach could possibly decrease American deaths before the age of 65 by two-thirds, even without further breakthroughs in medicine and nutrition. Prevention and Personal Responsibility The health-conscious individual can focus on four essential steps in maintaining health and preventing illness: positive attitude, a healthy diet, regular exer- cise and minimizing toxic exposures. Humanistic psychology emphasizes the importance of a positive mental attitude in preventing illness and maintain- ing health. The immune system and the repair mechanisms of tissues are well designed to ward off infection, to cure disease and to repair injury. DEPRESSION seems to diminish this capacity. For example, depression causes a drop in the production of interleukin, proteins that help regulate the immune response and help activate cancer-killing lymphocytes. Clinical statistics in the United States suggest psychological stress can harm the heart, increasing the risk of rehospitalization among patients with cardiac problems. Group therapy, meditation, and other practices may improve car- diovascular health in patients with clogged arteries by modifying their response to psychological stress. Susceptibility to disease reflects nutritional sta- tus; the nutritional environment affects the expres- sion of inherited traits. Either overnutrition or UNDERNUTRITION can set the stage for chronic ill- ness. Excessive fat consumption increases the risk of cancer and obesity, while inadequate amounts of most nutrients eventually lower the body’s defense against disease, including cancer. On the other hand, a healthy diet provides optimal amounts of all nutrients to assure health, while avoiding detri- mental food constituents. Probably the best strategies to avoid chronic ill- ness associated with aging are regular physical exercise coupled with wise food choices. A seden- tary lifestyle is linked to an estimated 250,000 deaths annually in the United States. Exercise decreases the risk of heart disease, stroke, high blood pressure (hypertension), adult onset dia- betes, osteoporosis (thin bone disease), and colon and breast cancer. Minimizing exposure to potentially damaging agents such as solvents, pollutants, and cigarette smoke is also important. The amount, type, and length of exposure to a toxic material at home or in the workplace affects health. Only recently have studies been undertaken to determine additive, long-term effects on health of continued low level- exposure to pesticides and industrial pollutants in food and water and air. (See also ANTIOXIDANT; BIO- CHEMICAL INDIVIDUALITY ; DEGENERATIVE DISEASES; DETOXIFICATION.) imitation fat See FAT SUBSTITUTE; OLESTRA; SIMP- LESSE . imitation flour See FLOUR SUBSTITUTE. imitation food A processed food that is nutri- tionally inferior to the real food. The designation “nutritionally inferior” on a food label means that the food contains 10 percent less of one or more nutrients than the food for which it substitutes. The food industry has devoted considerable finan- cial resources toward producing imitation food, most often substitutes for MEAT, FISH, dairy prod- ucts, and FRUIT. For example, SURIMI is imitation seafood. Compared to real foods, imitation foods often have a longer shelf life and may be tastier. Food additives are carefully selected for this pur- pose. Imitation foods are often less expensive than 358 imitation fat the real foods, but are generally less nutritious than the foods they replace because processing destroys or removes important nutrients. Relatively few nutrients are added back. Current regulations specify that food labels must list ingredients in descending order according to weight, meaning that the first ingredient listed is the most predominant. If the first item listed on the food label is one of the following, the food is likely to be fabricated or highly processed: any natural sweet- ener such as corn sweetener, high FRUCTOSE CORN SYRUP , HONEY, DEXTROSE, SUCROSE, or corn syrup solids; TEXTURIZED VEGETABLE PROTEIN; and sodium caseinate. The presence of artificial food colors, MSG ( MONOSODIUM GLUTAMATE), COCONUT OIL, palm or palm kernel oil, and PRESERVATIVES also indicates that the food is imitation or highly processed. (See also CONVENIENCE FOOD; FOOD ADDITIVES; FOOD LABELING.) immune system An elaborate, finely tuned defense system to destroy and counter the effects of viruses, bacteria, yeasts, and foreign substances that operate within tissues and cells and in the bloodstream. The immune system recognizes “self” from “nonself,” substances not part of the body. Another feature of the immune system is memory. It can remember previous invaders and mount a rapid response to them when they reappear. When the immune system is healthy, it destroys foreign elements without causing symptoms, but an imbal- anced immune system can set the stage for disease. Foreign substances and microorganisms may not be recognized or destroyed, resulting in chronic infection or even CANCER and AIDS. An imbalanced immune system can attack the body’s own tissues, creating AUTOIMMUNE DISEASES, or it can over- respond to common substances, creating allergies, such as food allergies. Organization of the Immune System The two branches of the immune system are “cel- lular immunity” and “humoral immunity.” The first depends on the active participation of different types of cells. Cellular immunity includes macro- phages, cells that engulf foreign invaders. These scavengers are amoebalike cells that surround and digest foreign particles, viruses, and bacteria. Macrophages live in tissues like the spleen (spleno- cytes), the LIVER (Kupffer cells), the lymph (wan- dering macrophages), the spinal cord, the brain (microglia), and connective tissue. Lymphocytes are an important type of white blood cell. T cells are highly specialized lympho- cytes that attack viruses, tumors, and transplanted cells and regulate the immune system. T cells are processed by the THYMUS GLAND. They work with B cells, which produce defensive proteins called ANTI- BODIES . In a typical scenario, macrophages first engulf foreign materials called ANTIGENS and trans- form fragments of the antigens for display on their cell surfaces. Certain T “helper” cells, acting as “generals,” “read” these antigens, and in turn stim- ulate the production of specialized T “killer” cells, foot soldiers that destroy abnormal cells or foreign materials. The gut is the largest immune organ, which is called the Gut-associated lymphoid tissue (GALT). GALT produces more antibodies than any other tissue in the body. The different types of immune cells communi- cate with each other via protein messengers called LYMPHOKINES. For example, macrophages produce a lymphokine called interleukin-1 to activate T helper cells, which in turn produce interleukin-2, to stimulate the production of the killer T cells. Helper T cells also produce gamma INTERFERON , which activates killer T cells. Mast cells are a type of T cell that lives in tissues and fights local infection. When they contact for- eign materials and cells, mast cells destroy them. Mast cells also release special chemicals like HISTA- MINE, as well as certain lymphokines that trigger inflammation marked by swelling ( EDEMA), red- ness, itching, sneezing, and runny nose. Lym- phokines also trigger phagocytes (macrophages) to destroy foreigners and dispose of signal proteins once they have done their work. Humoral immunity pertains to blood and lymph. It relies on cells that release defensive PRO- TEINS called complement and antibodies into the bloodstream to fight infection. Antibodies (gamma globulins) are Y-shaped proteins designed to target a particular antigen, by which a substance is recog- nized as being foreign. An antibody can neutralize the enemy either by binding to it or by targeting it for attack by other cells and chemicals. After anti- bodies bind foreign cells, complement ruptures them. Complement also triggers localized inflam- matory reactions, leading to common symptoms of immune system 359 pain, redness, and swelling, as well as to an increased concentration of defensive cells at the point of injury or infection. B cells, which originate in bone marrow, are a type of lymphocyte that yield plasma cells, special- ized to produce antibodies when exposed to foreign invaders. B cell proliferation, maturation, and anti- body production are stimulated by T helper infected cells. Another type of T cell, called T suppressor cells, gear down the immune system by turning off B cell production. Thus T suppressor cells limit aller- gic attacks and auto-immune reactions. Immunity Immunity is a hallmark of the immune system. The recovery from an infection renders the indi- vidual immune to subsequent attack by the partic- ular disease-causing agent. Immunity to chicken pox is a common example. The underlying mecha- nism relies on memory T and memory B cells in the bloodstream, which signal a red alert for a quick attack the next time a conquered virus in- vades again. These memory cells multiply rapidly when they again encounter any antigen they remember. Nutrients that May Benefit the Immune System The immune system requires a rich array of nutri- ents, including protein, FATTY ACIDS, VITAMINS, and MINERALS, for normal function. A JUNK FOOD diet can lead to overnutrition (too many calories and fat) and malnutrition (too little trace minerals and vitamins) that weaken the immune system. Mal- nourished individuals lacking adequate protein or calories are prone to disease. Low-level deficiencies of many nutrients seem to lower the effectiveness of the immune system. Supplements can boost immunity, especially in elderly people. It seems clear that a wise approach to support the immune system nutritionally includes a varied diet—reduc- ing fat to less than 30 percent of daily calories and emphasizing whole foods, FRUITS, and VEGETABLES, especially those rich in VITAMIN C, BETA-CAROTENE, and other carotenoids. Supplementing the diet with 100 percent of the RDA, ( RECOMMENDED DIETARY ALLOWANCE ) of B vitamins and trace min- erals for insurance may also be prudent when a diet is compromised by junk food or when the diet provides fewer than 1,600 calories. ANTIOXIDANT nutrients such as vitamin C, VITA- MIN E, SELENIUM, COPPER, MANGANESE, and beta- carotene may enhance immune responses by lowering the burden of FREE RADICALS, thus pro- tecting immune cells against the cumulative oxida- tion and free radical attack due to the release of powerful oxidizing agents as superoxide, hydrogen peroxide, and hydroxyl radicals. Vitamin C deficiency lowers the immune response in animal models. Adequate vitamin C increases T and B cell production and helps attack- ing cells migrate to sites of infection while making viruses and bacteria more sensitive to destruction. Furthermore, vitamin C acts as an antioxidant, and it protects cells against reactive chemicals produced by mast cells used to destroy foreigners. Vitamin E enhances both humoral and cell- mediated immunity, while vitamin E deficiency contributes to reduce T cells, killer cells, and macrophage function. Vitamin E supplementation boosts the immune system in elderly men and women consuming a typical diet, suggesting that older people require more vitamin E than specified by the adult Recommended Dietary Allowance to assure a fully functional immune system. Selenium is a cofactor for an important antioxi- dant enzyme, glutathione peroxidase, which neu- tralizes lipid peroxide that could damage the immune cells. Selenium works with vitamin E to stimulate the immune response to infection in experimental animals. Together they may help pro- tect against cancer. Selenium increases T helper cells and increases antibody production in experi- mental animals. However, excessive selenium depresses the immune system. Other specific nutrients support the function of the immune system: FOLIC ACID is required for immunity and lym- phocyte production. Folic acid is often deficient in the American diet. IRON is required to produce T and B cells. Iron deficiency is associated with increased incidence of common infection among children. MAGNESIUM is needed by the complement sys- tem to activate phagocytes. It is also required for antibody production. Americans typically do not consume enough magnesium. PANTOTHENIC ACID and VITAMIN B 6 help keep the lymphatic system and thymus gland healthy. 360 immune system VITAMIN A and beta-carotene help maintain thy- mus gland function during stress. Overproduction of cortisol, a stress-induced hormone from the adrenal glands, tends to shrink the thymus gland, which is critical for fully functioning T cells. Beta- carotene is the precursor of vitamin A. Limited studies suggest that beta-carotene may also stimu- late helper T cells. Studies of children in developing nations indicate that there is a direct relationship between vitamin A deficiency and decreased resis- tance to infection. On the other hand, excessive vitamin A can decrease immune system function. Vitamin B 6 plays an important role in maintain- ing optimal immunity, including antibody produc- tion and phagocytic activity. Vitamin B 6 deficiency impairs the immune system in a number of ways. It lowers cell-directed immune responses, de- scribed earlier, and leads to decreased thymus func- tion. Vitamin B 6 deficiency during gestation in experimental animals impairs immune functioning even in first and second generation offspring. ZINC helps maintain lymph glands and the thy- mus gland, thereby helping to fight chronic infec- tion. Zinc is required for many important enzymes, and it is not surprising that zinc deficiency decreases T cell and B cell function and macro- phage activity. However, too much zinc can depress immunity. Zinc, in combination with other trace minerals including copper, iron, and manganese, appears to improve B and T cell function in older people. Copper deficiency is associated with an increased risk of infection. Copper deficiency diminishes the effectiveness of the humoral system in lab animals. Copper is an essential component of SUPEROXIDE DISMUTASE, an antioxidant system, and CYTOCHROME C oxidase, an enzyme system required for energy production. Immunity, Stress, and Exercise Physical or emotional stress can alter hormonal output and immune response. A high level of stress increases the risk of illness and injury in the fol- lowing year and shortens the life span. Emotional well-being is supported by proper diet and regular physical EXERCISE. Moderately intense exercise increases the production of ENDOR- PHINS, the brain’s own opiates, which can bolster parts of the immune system. Studies indicate that interleukin-1 and interferon, which help the body respond to infection or injury, increase after mod- erate exercise. Moderate exercise also increases killer cell activity. Strenuous aerobic exercise may decrease effi- ciency of the immune system and temporarily increase susceptibility to illness by increasing the production of adrenal stress hormones. Among the hormones produced is cortisol, which limits inflammation by blocking the immune system. With continued stress, production of protective antibodies (such as secreted IgA, the antibody that protects the intestine and other body cavities against invasion by foreign substances). Chronic stress also decreases killer cell activity, increasing a person’s susceptibility to disease. (See also AGING; B COMPLEX ; ENDOCRINE SYSTEM; MALNUTRITION; NER- VOUS SYSTEM; PSYCHONEUROIMMUNOLOGY.) Chandra, R. K. “Nutrition and the Immune System from Birth to Old Age,” European Journal of Clinical Nutrition 56, supp. 3 (August 2002): 573–576. inborn errors of metabolism Abnormal gene products can cause metabolic imbalances, resulting in disease. Generally the inherited defect leads to the inadequate formation of an enzyme. Occasion- ally, inadequate formation of a COENZYME (enzyme helper) limits enzyme function or the protein- based signalling system that regulates a given enzyme’s function. Most genetic defects are classi- fied as autosomal recessive, meaning that they are not sex-linked. Full expression of the imbalance can occur only when both chromosomes contain the defective gene coding for a given enzyme and normal genes coding for that enzyme are absent. Examples of genetic diseases related to nutrients include familial HYPERCHOLESTEROLEMIA (high blood CHOLESTEROL), sickle cell anemia, GALACTOSEMIA, and PHENYLKETONURIA. PKU is an inherited inability to metabolize the essential AMINO ACID, PHENYLALA- NINE. PKU responds to nutritional intervention. During infancy and childhood PKU patients receive carefully balanced diets that provide only enough phenylalanine to support growth. Labels for foods containing the artificial sweetener ASPARTAME must warn phenylketonurics because of its pheny- lalanine content. (See also DNA; FOOD LABELING; MUTATION.) inborn errors of metabolism 361 Brusilow, S. W., and N. E. Maestri. “Urea Cycle Disorders: Diagnosis, Pathophysiology and Therapy,” Advances in Pediatrics 43 (1996): 127–170. indigestion See GASTROINTESTINAL DISORDERS . individuality See BIOCHEMICAL INDIVIDUALITY. induction The increased production of an ENZYME in response to external stimuli. Enzymes function as biological catalysts of cellular chemical reactions. The body can adapt to a limited extent to changes in the diet and to environmental influ- ences by altering the levels of enzymes in a given tissue. For example, a high-carbohydrate diet leads to increased production of AMYLASE, the starch- digesting enzyme of the pancreas. Starvation decreases levels of digestive enzymes and enzymes responsible for fat and glycogen synthesis but induces enzymes required for fat and carbohydrate degradation. Enzymes that synthesize BLOOD SUGAR (glucose) from amino acids are also induced by starvation. Excessive alcohol consumption induces liver alcohol oxidizing systems so that alcohol will be cleared from the blood more efficiently. Similarly, many medications induce liver enzymes responsi- ble for drug degradation. Certain cellular enzyme levels increase in response to hormones and to growth promoters. Examples include the hor- mones ESTROGEN (female sex hormone), CORTISOL (adrenal hormone regulating energy metabolism and degradation), and GROWTH HORMONE (a pitu- itary hormone involved both in growth and main- tenance of tissues, especially muscles). INSULIN provides the broad impetus for increased enzyme production in many tissues. Insulin from the PAN- CREAS is perhaps the most general anabolic hor- mone; that is, it promotes enzymes leading to the accumulation of protein, fat and carbohydrates. (See also DETOXIFICATION.) infant formula A manufactured food designed to nurture the infant during the first year of life, until weaning. Commercial infant formulas are either nonfat cow’s MILK-based or soybean-based. Com- mon formulas are available in powdered form, as concentrates, or as ready-to-feed liquid with no prior preparation. No formula exactly reproduces human milk; on the other hand, formulas can pro- vide adequate nutrition for babies. In the late 1970s, production of chloride- deficient formulas caused delayed speech, slowed growth, and poor muscle control in babies who had consumed the products. Partially in response to this disaster, Congress passed the Infant Formula Act of 1980, which mandates the U.S. FDA to see that this synthetic food meets nutrient standards based upon the American Academy of Pediatrics’ recommendations to assure infant growth and development. In 1982, the FDA adapted quality-control proce- dures to monitor the production of this food. As a result, infant formulas are nutritionally similar though not identical to BREAST MILK in total pro- tein, total fat, calcium-to-phosphorus ratio, energy content (calories/100 ml), content of the essential fatty acid linoleic acid, and electrolytes (sodium, potassium, chloride). There are advantages to infant formulas. There is no limit to the supply, and a mother has greater freedom to care for other children or to return to work. Other family members can participate in feeding sessions, developing the warmth of that association. The mother of a formula-fed infant can offer the same closeness and stimulation as the BREAST-FEEDING mother. In 1998 an estimated 29 percent of women in the United States were breast-feeding their infants 6 months after leaving the hospital. Several weeks of breast-feeding assures that the mother’s antibod- ies will be present in the infant. Cow’s milk formula resembles its source in terms of type of milk protein, total fat, and calcium to phosphorus ratio. It has been adjusted so that the total protein content, carbohydrate, fat, major minerals, linoleic acid, and vitamins are similar to breast milk. The La Leche League International does not recommend substituting formula or breast milk with cow’s milk until the baby is a year old or older (eating the equivalent of three baby food jars of solid food per day). Unprocessed cow’s milk is not a suitable food for infants for many reasons. Cow’s milk contains three times as much protein as human milk, and this protein is more difficult for babies to digest. Manufacturers either presoften or predigest this protein, or they add whey to 362 indigestion adjust the protein ratio. Butterfat is also poorly digested by infants; therefore it is replaced by veg- etable oils. Because the higher concentration of phosphate and other dissolved minerals in cow’s milk increases the burden on immature kidneys, minerals are adjusted to resemble breast milk. Lac- tose or corn syrup solids are used to adjust the car- bohydrate content. Bovine milk protein contains much more of the essential amino acid phenylala- nine than human milk protein. This situation could affect infants who cannot tolerate high phenylala- nine for genetic reasons (see PHENYLKETONURIA). Cow’s milk in infant formulas sometimes trig- gers an ALLERGY, especially if there is a family his- tory of allergies. Cow’s milk-based formula as a supplement to breast-feeding is less of a problem when the baby is six months or older. For infants who are sensitive to cow’s milk, liq- uid formulas containing soy protein fortified with the essential amino acid methionine and with soy- bean oil are available. A variety of formulas are prepared from coconut oil and corn oil, but these oils contain very little alpha linolenic acid, an essential fatty acid. Human milk contains substan- tial amounts of a large fatty acid called DOCOSA- HEXAENOIC ACID (DHA). DHA, which is necessary for normal brain and eye development, is not added to formula. There is a consensus that for- mula should at least contain linolenic acid, the pre- cursor of DHA, which the infant’s body may convert to DHA. A wide variety of infant formulas is available to meet special needs. Infants with lactose intolerance can drink formulas in which lactose is replaced by other carbohydrates. Formulas can be adapted to adjust protein ratio, linoleic acid content, or to lower sodium content. Special formulas are avail- able for preterm babies. Ready-to-use formula, as well as powdered formula, sometimes contains ALUMINUM. This is not a problem for babies with normal kidneys; however, premature babies may tolerate it poorly. CARRAGEENAN-containing formula should not be given to premature infants. This SEAWEED product is used to stabilize fat by forming gels in milk. In the past, the infant formula industry employed questionable marketing practices in developing countries, which led to a 1977 con- sumer boycott against the Swiss-based Nestlé com- pany. For example, they dressed staff in hospital garb while introducing infant formula to new mothers, and used misleading ads. In 1979, Nestlé, which accounted for 50 percent of formula sales to the developing world, and the U.S. government formally agreed to voluntary guidelines that banned marketing abuses in developing nations. In 1981, the United Nations World Health Orga- nization voted overwhelmingly to approve an international code of conduct to restrict advertising and marketing of baby formula, which can lead to infant malnutrition and death when improperly used. Although not binding, the new guidelines apply to infant formula promotion in industrialized nations as well as developing nations. Proper use of infant formula is often impossible in poorer areas of the world, where the water used to mix the for- mula is often contaminated. (See also BABY FOOD.) Ryan, A. S. “The Resurgence of Breast-feeding in the United States,” Pediatrics 99, no. 4 (1997): e12. Scariati, Paula D. “Risk of Diarrhea Related to Iron Con- tent of Infant Formula: Lack of Evidence to Support the Use of Low-Iron Formula as a Supplement for Breast-fed Infants,” Pediatrics 99, no. 3 (1997): e2. inflammation A defensive response by the body to irritation, injury, or infection usually character- ized by heat, redness, swelling, and pain at the injury site. This response is triggered by physical agents, chemical agents, or disease-producing organisms. Swelling is due to increased blood ves- sel leakage of fluids, and redness is due to the increase in diameter of blood vessels, (especially capillaries) so that they carry more blood. With increased vessel leakage, substances normally retained in blood such as water, antibodies, phago- cytic cells, and clot-forming components, migrate into tissues at the site of injury. Cellular Materials that Promote Inflammation HISTAMINE, kinins, PROSTAGLANDINS, LEUKOTRIENES, and complement contribute to inflammation. Hist- amine, derived from the amino acid HISTIDINE,is released from white cells (basophils), mast cells, and other cells when injured. Kinins are proteins that induce vasodilation, increase vessel leakiness, attract phagocytic cells, and cause pain. Prosta- glandins are hormone-like materials that function inflammation 363 in the immediate area where they are produced. They play many roles, including intensifying pain and promoting fever, which helps combat infec- tions. Leukotrienes are extremely powerful inflam- matory agents. Complement is a group of blood proteins that stimulate histamine release, destroy bacteria, and promote phagocytosis (engulfing other cells and fragments). Pain can result from injured nerves or from irritation by released micro- bial products. Inflammation generates free radicals, which are highly damaging chemical fragments. Chronic inflammation therefore can produce cellu- lar damage and oxidative stress, leading to an unbalanced immune response. Many chronic degenerative diseases involve inflammation and oxidative damage. Examples include rheumatoid arthritis, atherosclerosis, as well as side effects resulting from radiation and chemotherapy during cancer treatment. Nonsteroidal anti-inflammatory drugs (NSAIDS) are often used to combat inflammation. These drugs, which are often nonprescription items, can themselves cause damage to the stomach or intesti- nal lining; in some instances they may harm the liver when used in excess. (See also ASPIRIN; IMMUNE SYSTEM.) inflammatory bowel disease (IBD) A chronic inflammation of the intestinal wall involving painful swelling and open sores. Eventually, the intestinal wall becomes scarred, which narrows the intestinal opening. IBD affects 1 million to 2 million Americans. It differs from CELIAC DISEASE,a grain (especially wheat) intolerance, and from IRRI- TABLE BOWEL SYNDROME (spastic colon), a much more common, less serious condition involving muscle contractions, rather than chronic inflam- mation. Two distinct disorders are classified as inflammatory bowel disease: CROHN’S DISEASE and ulcerative COLITIS. Crack-like ulcers and abnormal granular growths in the intestine often accompany Crohn’s disease, while ulcerative colitis occurs only in the large intestine and involves inflammation and ulceration. IBD symptoms include persistent (sometimes bloody) DIARRHEA, flatulence, cramps, low-grade fever, and weight loss, as well as problems such as ARTHRITIS and inflamed eyes or skin. Children may be affected by retarded growth and retarded sex- ual development. IBD increases the risk of colon CANCER. IBD is reported mainly in developed countries, where it is most common between the ages of 12 and 40. The causes of IBD are unknown. It does not seem to be caused by stress. One theory is that IBD is an AUTOIMMUNE DISEASE in which the per- son’s own immune system attacks the intestine. Clearly, immune imbalances seem to play a part. Another view is that bacteria, viruses, or toxic chemicals initiate IBD. Food sensitivity has also been implicated in some cases. Conventional medical treatment involves drugs and/or surgery. Drugs reduce inflammation and can lead to a remission. However, steroids have side effects like high blood pressure, diabetes, and thinning of bones. Typical treatment recommenda- tions include: • Eating a well-balanced diet that provides ade- quate nutrients to maintain and repair the intestinal tract. It is important to correct any nutrient deficiencies caused by the disease (especially iron, folate, and calcium). • Eating several small meals throughout the day. This may be more effective for good digestion and assimilation than eating three big meals. • Avoiding irritating foods that could increase inflammation. These differ from person to per- son, though seeds, nuts and corn, lactose and dairy products, fried or greasy foods, and coffee are often the culprits. • Getting enough exercise and managing stress. Severe stress suppresses the immune system and encourages inflammation. • Seeking expert medical advice. The National Foundation for Ileitis and Colitis provides important information to patients and their families. Gross, V. et al. “Free Radicals in Inflammatory Bowel Dis- eases—Pathophysiology and Therapeutic Implica- tions,” Hepato-Gastroenterology 41 (1994): 320–327. inhibition Restricting the activity of a cellular or physiologic process. Several different mechanisms are involved in inhibition. Hormones Hormones may serve as inhibiting agents because they can inhibit the release of other 364 inflammatory bowel disease hormones. Thus, the ovaries produce inhibin (a hormone that inhibits the secretion of the ovarian hormones), follicle stimulating hormone, and lut- enizing hormone, at the end of the menstrual cycle. Elevated CORTISOL from the adrenal glands inhibits the release of ADRENOCORTICOTROPIN (ACTH) from the PITUITARY GLAND. ACTH stimulates the release of cortisol. Enzymes Enzymes are protein catalysts that lose activity when blocked by inhibitors. Competi- tive enzyme inhibitors are compounds that mimic the chemical that the enzyme usually alters. Enzyme poisons like toxic heavy metals— LEAD, MERCURY, and CADMIUM—can bind to enzymes without competing with substances and can per- manently inactivate enzymes. Certain key regulatory enzymes may be re- versibly inhibited by the accumulation of key prod- ucts of metabolism. One example is the feedback inhibition of a METABOLIC PATHWAY , a sequence of functionally linked enzymes. In this type of inhibi- tion, a surplus of the final product of the pathway can inhibit the pathway. For example, the buildup of ATP, the energy currency of the cell, can inhibit enzyme systems like GLYCOLYSIS that generate ATP. Such feedback mechanisms help the cell avoid wasteful overproduction of products. (See also ENDOCRINE SYSTEM; INDUCTION.) inosine One of the basic compounds composing cells and a precursor to adenosine, an important energy molecule and building block of DNA and RNA. Although some European scientists believed it could have energy-boosting effects, controlled studies concluded that inosine does not improve athletic performance. Athletes often take between 5,000 and 6,000 mg of inosine a day, but research does not support the use of this supplement in any amount. However, some animal research studies have suggested it may be helpful in the treatment of stroke and other central nervous system disorders. Inosine occurs in organ meats and brewer’s yeast and can be taken as a supplement. Although there are no reports of side effects, any inosine that is not used by the body is converted to uric acid, which could be a problem for people at high risk for gout. Safety data are inadequate for pregnant and breast- feeding women. Starling, R. D., T. A. Trappe, K. R. Short et al. “Effect of Inosine Supplementation on Aerobic and Anaerobic Cycling Performance,” Medicine and Science in Sports and Exercise 28 (1996): 1,193–1,198. inositol (myoinositol) An essential building block of cell membrane LIPIDS . Chemically, inositol is a cyclic ALCOHOL with six hydroxyl groups, one per carbon atom. Inositol is a constituent of phos- phatidylinositol, a component of inner-cell mem- branes. Derivatives of inositol function as HORMONE relay signals in cells. Diverse hormones such as VASOPRESSIN (from the pituitary gland), EPINEPHRINE (from the adrenal gland) and releasing factors from the HYPOTHALAMUS stimulate the release of inositol triphosphate from phosphatidylinositol. Animal studies show that inositol may protect against ATHEROSCLEROSIS and against hair loss. Inos- itol is also supposed to help reverse nerve damage caused by diabetes in animals. Oral supplementa- tion in human diabetics has not verified this result. Diabetics should consult their health care providers before taking inositol supplements. Inositol has a low toxicity. Nutritionists have not yet established the opti- mum amount of inositol in the diet. It is widely dis- tributed in food and is also manufactured in the body. Sources include CITRUS FRUIT (except lemons), CANTALOUPE, whole grain bread, cooked beans, green beans, and nuts. Inositol occurs in grains such as PHYTIC ACID, in which six phosphate groups are attached to the inositol molecule. Phytic acid can bind minerals and limit their uptake. Safety data are inadequate for pregnant and breast- feeding women. (See also VITAMIN .) Shamsuddin, Abulkalaman M. “Inositol Phosphates Have Novel Anti-Cancer Function,” Journal of Nutrition 125, supp. 3 (1995): 725S–732S. insulin A protein HORMONE, secreted by beta cells in the PANCREAS, that stimulates the uptake of BLOOD SUGAR by many tissues. Insulin counteracts the effects of GLUCAGON, the pancreatic hormone responsible for raising blood sugar. Insulin is used therapeutically to treat DIABETES MELLITUS and is either purified from pork or beef pancreas or is ge- netically engineered of human origin. Insulin is produced by small cell clusters in the pancreas insulin 365 [...]... produced by the stomach lining and required for intestinal absorption of VITAMIN B12 Gastric PARIETAL CELLS normally secrete intrinsic factor during digestion Intrinsic factor binds tightly vitamin B12 released from food during intestinal digestion The resulting B12-intrinsic factor complex is selectively absorbed by the epithelial cells lining the ILEUM, the latter portion of the small intestine If the stomach... patients exhibit a degree of insulin resistance In non-insulin-dependent diabetes (Type II diabetes), there is a loss of insulin sensitivity and a decline in the maximal response elicited by insulin According to one scenario the problem may reflect the inability to use insulin effectively because of too few insulin binding sites on target cells Thus, insulin resistance can be caused by defective insulin receptors... intestine is the major site of digestion and uptake of nutrients, including CARBOHYDRATE, AMINO ACIDS, FATTY ACIDS, WATER, MINERALS, and VITAMINS released by stomach and intestinal secretions The small intestine begins at the valve regulating the opening of the stomach (pyloric sphincter) and coils its way through the abdominal cavity before joining the large intestine The average diameter of the small intestine... permit adequate vitamin B12 assimilation when intrinsic factor and stomach acid production are low Because FOLIC ACID also supports cell proliferation similar to vitamin B12, folic acid is usually administered with vitamin B12 (See also ACHLORHYDRIA; AGING; SENILITY.) inulin A POLYSACCHARIDE that is composed primarily of the simple sugar FRUCTOSE Inulin plays a minor role in the diet; it is found in... defensive cells of the immune system Interstitial fluid contains white BLOOD cells (LEUKOCYTES) that also enter tissue fluid from the bloodstream by squeezing through capillary walls and migrating to the site of infection and inflammation Interstitial fluid, together with blood and lymph, help maintain the internal environment within normal limits When interstitial fluid flows through lymphatic vessels, it is... organisms and keeps them from attacking the mucosal cells, often a prerequisite for infection It also binds specific antigens like food proteins and prevents their penetration Stress can lower secretory IgA production, increasing the likelihood of intestinal imbalance and infection Colon (Large Intestine) The large intestine is about one-quarter of the length of the small intestine and averages 2.5 inches... to VITAMIN B12 deficiency, nor will iron cure anemias based on other nutritional deficiencies such as vitamin B6 A variety of laboratory tests are used to evaluate iron deficiency The most sensitive clinical test for mild iron deficiency measures serum ferritin Serum ferritin may decline to 12 mcg/liter without visible symptoms With serious iron deficiencies, the level of the iron-transport protein in the. .. side effects include rash and allergies Iodized Salt In the United States, sodium iodide has been added to table salt (sodium chloride) since 1924 to create “iodized salt.” With 76 mcg of iodine per gram of salt, this ENRICHMENT was responsible for the virtual disappearance of goiter in the United States Small iron 371 amounts of additives stabilize iodine in iodized salt and prevent caking: They include... thrive without oxygen, while others can live under both aerobic and anaerobic conditions Bacteria implant in the infant’s intestine shortly after birth Bifidobacterium infantis is promoted by BREAST-FEEDING Later in life, a full complement of bacteria is normally in place Different bacteria favor different regions of the intestine Bifidobacterium bifidum is a major component of the large intestine in... intestine is 1 inch and the length is about 20 feet in an adult The surface of the small intestine looks like a wrinkled shag rug, which increases the efficiency of nutrient absorption The highly convoluted surface is coated with fuzzy, microscopic projections called VILLI There are 10 to 40 villi per square millimeter Cells lining the small intestine possess microscopic, hairlike projections called MICROVILLI, . Responsibility The health- conscious individual can focus on four essential steps in maintaining health and preventing illness: positive attitude, a healthy diet, regular exer- cise and minimizing. resistance. In non-insulin-dependent dia- betes (Type II diabetes), there is a loss of insulin sensitivity and a decline in the maximal response elicited by insulin. According to one scenario the problem. psychological stress. Susceptibility to disease reflects nutritional sta- tus; the nutritional environment affects the expres- sion of inherited traits. Either overnutrition or UNDERNUTRITION can set the