The Encyclopedia Of Nutrition And Good Health - T ppsx

T 612 table salt See SODIUM. table sugar See SUCROSE. tahini A butter prepared from ground, hulled SESAME seeds. Tahini prepared from untoasted seeds has a mild flavor and is easily spreadable. Toasting sesame seeds yields a more oily mixture and adds a stronger flavor. Most commercial production of sesame seeds occurs in Mexico and Guatemala. Like sesame seed, tahini is a vegetarian source of iron. One tablespoon (15 g) provides 91 calories; protein, 2.7 g; carbohydrate, 2.7 g; fiber, 2.2 g; fat, 8.5 g; iron, 0.95 mg; thiamin, 0.24 mg; riboflavin, 0.02; mg niacin, 0.85 mg. tallow FAT extracted from fatty tissue of sheep and cattle. Tallow hardens at room temperature, reflecting its relatively high content of saturated FATTY ACIDS; it contains about 46 percent saturated fatty acids and only 4 percent polyunsaturated fatty acids. Beef tallow is used in prepared foods such as chili and refried beans and french fries. It is also used industrially in soap and candle manufacture. Fat regardless of its source yields nine calories per gram, more than double the amount of calories in carbohydrate. (See also FAT METABOLISM; LARD.) tamari (natural shoyu, Japanese soy sauce) A soy sauce prepared from the formation of SOYBEANS and cracked, roasted WHEAT. Tamari is fermented slowly and no preservatives are added. Tamari is a salty food containing 16 percent salt. Tamari contains little vitamin B 12 activity. tangelo A citrus fruit that is a result of cross- breeding a grapefruit and a tangerine. They have fewer seeds than tangerines but retain most of that fruit’s flavor and sweetness. They are generally eas- ier to peel and eat because the skin is somewhat loose around the pulpy flesh. The fruit has existed for several thousand years, probably originating in Southeast Asia from an accidental cross-breeding of mandarin oranges and pomelos (an ancestor of the modern grapefruit). Like other citrus fruits, tangelos are rich in vitamin C. One medium tangelo provides 60 calories; fiber, 3 g; potassium, 240 mg. tangerine A smallish, tart CITRUS FRUIT . Tangerine is a descendant of the mandarin ORANGE and origi- nated in China. The fruit has a thin, easily peeled skin and segments separate readily. Unlike oranges, which can be stored at room temperature for several weeks, tangerines need to be refrigerated if kept longer than a couple of days. They are eaten raw or used in fruit or gelatin-based salads. Tangerines provide less vitamin C than oranges. The edible portion of one raw tangerine (84 g) provides 37 calories; protein, 0.5 g; carbohydrate, 9.4 g; fiber, 1.6 g; fat, 0.2 g; potassium, 132 mg; vitamin C, 26 mg; thiamin, 0.09 mg; riboflavin, 0.02 mg; niacin, 0.13 mg. tannins A family of complex compounds that occur in the bark or leaves of certain plants and trees. Tannins are classified chemically as flavonoids they are composed of two or more aro- matic ring structures that act as antioxidants to quench oxidative damage due to FREE RADICALS. Polyphenols block the ability of certain compounds to cause mutations in test tube experiments and inhibit lung and skin tumors in experimental animals. Tannins are classified as hydrolyzable or con- densed. Hydrolyzable tannins such as ellagic acid, gallic acid, and related compounds, are often com- plexed with glucose. Hydrolyzable tannins could serve as anticancer agents, increasing the liver’s ability to “detoxify” potential cancer-causing agents by increasing their water-solubility, thus speeding up their removal (excretion). A second type, con- densed tannins (flavolans), are chains of polyphe- nol units that do not break down readily and combine with iron and other metals. Individuals consuming COFFEE, TEA, COCOA, and CHOCOLATE may ingest on the order of 1,000 mg of tannins daily. Tannins occur in all coffees, even decaffeinated coffee. A child consuming chocolate milk together with chocolate candy could consume 160 mg of cocoa tannin per kilogram of body weight per day. Brewed teas supply tannins. Some population studies suggest that tea drinkers have a reduced risk of dying from coronary heart disease. High levels of tannic acid can bind protein and limit digestion, limit the uptake of GLUCOSE and METHIO- NINE, and bind iron from vegetable sources. Acute toxicity tests with adult animals did not indicate toxicity. tapioca A form of starch derived from the CAS- SAVA, a tropical root vegetable. Tapioca is prepared by drying pulped roots after fibers have been removed. Special grinding and sieving is required to produce the type of tapioca used in popular puddings. Like most starches, tapioca swells and thick- ens when cooked in water. It is often used to thicken soups, pies, and puddings. High-grade tapioca forms milky beads with a brilliant white luster. The nutrient content of 1 cup (165 g) of tapioca cream pudding is: 221 calories; protein, 8.3 g; carbohydrate, 28.2 g; fat, 8.4 g; sodium, 257 mg; calcium, 173 mg; thiamin, 0.07 mg; riboflavin, 0.30 mg; niacin, 0.2 mg. (See also FLOUR.) tardive dyskinesia A disabling disorder sometimes produced by the long-term use of anti- psychotic drugs and neuroleptic drugs (tranquiliz- ers). Tardive dyskinesia occurs in 10 percent to 20 percent of patients treated with these drugs. Symp- toms include involuntary twitching of mouth and face, hand trembling, spasms, and speech distur- bances. Sometimes these drug-induced effects are irreversible. Supplements of the nitrogen-containing nutrient CHOLINE and of LECITHIN, the PHOSPHOLIPID from which choline is derived, reduce the abnormal movements of tardive dyskinesia, and lecithin remains an important treatment option. TRYPTO- PHAN , together with NIACINAMIDE and VITAMIN B 6 , may relieve symptoms of tardive dyskinesia. Large- scale studies have suggested that patients who supplement with NIACIN, MANGANESE, and ZINC concomitantly with drug treatment experience decreased symptoms of tardive dyskinesia. The American Psychiatric Association concluded (1991) that the general clinical value of such nutrients should be confirmed with long-term, large-scale studies before acceptance. Preliminary clinical studies suggest that VITAMIN E may also decrease the severity of symptoms. (See also NERVOUS SYSTEM; PARKINSON’S DISEASE.) Dannon, P. N. et al. “Vitamin E Treatment in Tardive Dyskinesia,” Human Psychopharmacology 12 (1997): 217–220. target heart rate See EXERCISE. taro (Colocasia esculenta) A tropical, tuber-bear- ing plant native to Southeast Asia. Taro cultivation gradually spread to Japan, China, the eastern Mediterranean region, Polynesia, New Zealand, West Africa, and South America. Taro root is a high-carbohydrate food. Poi, a staple food of Poly- nesia, is made from the taro root. A common variety of taro produces a brown-skinned root with a pale purple or white flesh. Taro root is sold in Asian markets and specialty shops. Taro leaves should not be consumed raw because some varieties contain high levels of OXALIC ACID (calcium oxalate) that can be toxic when large amounts are consumed. Taro root can be used like potatoes; it is boiled, baked, or steamed. The vegetable becomes very sticky upon cooling. The tuber has a nutrient value similar to the Irish POTATO. tarragon (Artemesia dracunculus) A small perennial shrub with a dark green, narrow leaf that is used as a culinary HERB. The name comes from the French estragon, meaning “little dragon,” because the twisted roots resemble dragons. Tar- ragon is used fresh or dried to create a somewhat anise-like flavor in chicken, veal, and turkey tarragon 613 dishes; in broiled fish and shellfish; omelet and egg dishes; MUSTARD; and MAYONNAISE. Tarragon is used in bearnaise sauce. Tarragon can overwhelm other seasonings, and it is not recommended in recipes calling for a blend of herbs. (See also ANISE; SPICE.) tartaric acid An acidic FOOD ADDITIVE used to create a tart taste. Tartaric ACID occurs widely in plants, especially in fruits and ripe grapes. Com- mercially, tartaric acid is a by-product of wine production. Tartaric acid is used with grape flavors and other flavoring agents in SOFT DRINKS, CANDY, gelatin-based desserts, and YOGURT. The potassium salt of tartaric acid (potassium tartrate) is called “cream of tartar.” This compound is used as a leavening agent and as an anticaking agent in baking. A mixture of sodium tartrate and sodium-potassium tartrate, “Rochelle salt,” is used to control acidity and to emulsify ingredients of processed foods ( CHEESE and jam, among others). Intestinal bacteria produce most of the tartaric acid people ingest, and it is considered a safe food additive. (See also CITRIC ACID.) tartrazine (FD&C yellow no. 5) One of the most widely used artificial colorings in the United States. Low levels of tartrazine are used in beverages like SOFT DRINKS; higher levels are used in BREAKFAST CEREALS , baked goods and snack foods. Health con- cerns have been raised because tartrazine causes allergic reactions in certain people, particularly if they are sensitive to ASPIRIN. Asthma, hives and typical “hay fever” symptoms can occur, although more severe symptoms have been reported. Tar- trazine sensitivity was estimated to be prevalent in less than 100,000 Americans in the late 1970s. In 1981 the U.S. FDA required that ingredient labels on foods disclose the presence of tartrazine rather than simply noting “artificial coloring.” Several Euro- pean countries have banned this dye from food use. Coloring from TURMERIC and ANNATTO can be used in place of this yellow food coloring. (See also ALLERGY, FOOD; FOOD ADDITIVES; FOOD SENSITIVITY.) taste The flavor sensation of substances placed in the mouth. The sensation of taste relies on the stimulation of receptors (taste buds) by substances dissolved in SALIVA. An adult possesses about 2,000 taste buds located chiefly on the tongue. They occur also on the soft palate and in the throat. Typ- ically, taste buds occur in small protuberances called papillae, which give the upper surface of the tongue a rough appearance. Taste buds possess external cells with hair-like extensions that project through a central taste pore. When a dissolved substance enters a taste pore and contacts the hair-like projections, it can generate a nerve impulse that is relayed to the brain. Of all the seemingly endless different flavors and subtle tastes, there are only four basic taste sensations: sweet, sour, salt, and bitter. Most other tastes are combinations of these modified by odors. When a person has a cold, the olfactory sensations ( SMELL) do not operate normally, although the taste sensations may be normal. The olfactory system (sense of smell) is much more sensitive to stimulation than the gustatory system for a given concentration of a substance. Taste buds located in different areas possess different sensitivities to taste sensations. Thus, the tip of the tongue reacts with all primary taste sensations, but it is highly sensitive to salty and sweet materials. The edges of the tongue respond more readily to sour substances, while the back of the tongue responds most to bitter substances. Foods that taste bitter are generally rejected. This may be part of a protective mechanism in human evolution, because many poisonous plants contain toxic substances that produce a bitter taste. A degree of saltiness is often considered pleasant but very salty foods will be rejected. The preference for salty foods in most people is acquired. Gradu- ally, reducing the amount of salt in foods will uncover the subtle, rich flavors of minimally processed foods. Sweet tasting foods create pleasur- able feelings. ARTIFICIAL SWEETENERS have been developed that will trigger the sweet receptors without contributing calories. A sour taste may be either objectionable or desirable. Dilute acid solu- tions such as VINEGAR can create tangy, zestful foods and beverages, while excessive acidity is not palatable. The taste threshold varies for each primary taste. Bitter substances possess the lowest taste threshold, that is, they can be distinguished at low concentrations; the threshold for sour sub- 614 tartaric acid stances is higher; and the thresholds for salt and sweet materials are higher than for sour or bitter foods. Adding sugar to highly seasoned dishes increases the ability to sense hot spices. Children up to the age of five have more taste buds than adults, so foods taste richer to them. Babies explore their environment by tasting every- thing they can reach. Possible reasons for a decrease in the sense of taste include: cigarette smoking, eating excessively salty foods or drinking alcoholic beverages, and a ZINC deficiency. Elderly persons gradually lose some of their sense of taste; food tends to taste bland to them. Adler, E. et al. “A Novel Family of Mammalian Taste Receptors,” Cell 100 (March 17, 2000): 693. Fackelmann, K. A. “The Bitter Truth,” Science News 152 (July 12, 1997): 24. taurine A sulfur-containing compound produced by the liver. Taurine serves multiple functions. The liver uses taurine to convert CHOLESTEROL to BILE salts, required to digest FAT and to modify toxic chemicals to help flush them out of the body. Tau- rine helps regulate nerves and muscles and supports SODIUM and POTASSIUM transport across cell membranes. It is required for normal function of the heart, brain, eyes, and vascular system. Taurine is the most prevalent free amino acid in the heart, where it contributes to muscle contraction. With chronic stress and when the oxygen supply to the heart drops (ischemia), taurine levels in the heart decrease. In Japan, taurine is used in treating HEART DISEASE and congestive heart failure. Taurine administered to experimental animals can prevent induced heart muscle damage. In the brain, taurine acts as a NEUROTRANSMITTER, a chemical released by a nerve cell (neuron) to help carry a nerve impulse to an adjacent cell. Taurine seems to be inhibitory, that is, it depresses the brain. Therefore, it is being studied as an anticonvulsant in the treatment of epilepsy. Taurine is also involved in calcium metabolism of the brain. The body possesses a limited capacity to produce taurine, and certain individuals may require dietary taurine, depending on their nutritional status. Pre-term and full-term infants do not synthe- size appreciable taurine, which is the most abundant amino acid in breast milk. With time the taurine content of breast milk declines as the infant grows and begins to manufacture taurine. Taurine was once omitted from infant formulas; now it is added routinely. Taurine is concentrated in animal protein, especially organ meats, fish, and milk, but is absent from plant foods. Taurine is a nerve depressant and when used as a supplement it may affect short-term memory. Its use is considered experimental. (See also METHIO- NINE ; NERVOUS SYSTEM.) tea (Camellia sinensis) The dried leaves of a tropical evergreen that grows as a small tree or shrub. Brewed tea is the most popular beverage worldwide. The origin of tea is obscure, though it probably orig- inated in regions of Tibet, western China, and north- ern India. India, Sri Lanka, and China are the leading tea growing countries. Flower, leaf, bark, roots, and seeds of various plants are used in herbal teas but these are not derived from Camellia sinensis. Differences in color and aroma among various types of tea reflect primarily differences in tea processing. Nearly 75 percent of tea ends up as black tea, in which leaves are crushed to release enzymes that oxidize substances in leaves (polyphenols) that create the rich flavor. The leaves are then dried in hot air to develop a brown/black color. For green tea, fresh leaves are steamed to destroy the oxidiz- ing enzymes, then rolled and dried. Instant tea was developed in the United States in 1948. It is prepared by brewing a strong tea and removing water to leave a dried concentrate, which can be added to water. Oolong tea is partially fermented to create a green-brown leaf. Brewed tea is prepared by pouring boiling water over dried tea leaves. Generally, the best flavor is obtained when tea has steeped (soaked) in boiled water for up to five minutes for black tea, one to two minutes for green tea. Longer steeping creates tea with more TANNIN and increased bitterness. Black tea, and to a lesser extent, green tea bind iron because of the tannin content. Tannins contribute to the pungency of tea. Tea is a mild stimulant because it contains CAFFEINE. A cup of black tea provides about 90 mg, about half the amount in COFFEE (160 mg/cup). Green tea contains up to 30 tea 615 mg per cup. Caffeine increases urination and is responsible for the diuretic effect of tea. Brewed tea contains other substances as well. Tea is a source of FLUORIDE; a cup of tea provides about 0.3 mg. Green tea yields more fluoride and less caffeine than black tea. Green tea provides vitamin C; on the average, one cup of green tea provides as much vitamin C as half a cup of orange juice. Tea also contains tannin and catechin (classified as FLAVONOIDS), widely distributed among plants. Cancer of the esophagus, stomach, and intestine are rare in regions of Japan and China where large amounts of green tea are consumed. They possess ANTIOXIDANT properties. Epigallocate- chin is the most potent catechin in tea. It is reported to be 200 times stronger antioxidant than vitamin E. Antioxidants have been proposed as anti-cancer agents. Studies have shown that green tea extracts can inhibit the growth of bladder, stomach, and esophageal cancer cells. Population studies suggest that regularly drinking green or black tea can lower the risk of developing cancer. Other studies link tea consumption with a lowered risk of dying from heart disease. In one study, people who drank more than two cups of tea daily reduced the risk of death following heart attack by 44 percent. Tea flavonoids may limit the oxidation of LOW-DENSITY LIPOPROTEIN (LDL) cholesterol, believed to be an early event in atherosclerosis. Other studies suggest that tea can increase bone density, inhibit the bacterium responsible for tooth decay, improve the growth of beneficial gut bacteria, and inhibit flu virus and boost the immune system. However, the mechanism of action of tea flavonoids is still being investigated. Imai, K. “Cross-sectional Study of Effects of Drinking Green Tea on Cardiovascular and Liver Diseases,” British Medical Journal 310 (1995): 693–696. teeth Bony projections from the upper and lower jaws used for chewing food. Each tooth possesses an exposed crown and one or more roots that anchor the tooth in the jawbone. Each jaw has 16 teeth. A child may develop up to 20 teeth that are replaced with permanent teeth. Incisors and cus- pids (canines) are for biting off pieces of food. Bicuspids (premolars) and molars provide grinding surfaces to pulverize food. The outer coating of the tooth is called the enamel, the hardest part of the tooth. This protective layer resists the wear of chewing and the action of bacteria. A hardened type of bone covers the roots. Dentine, a hard, mineralized layer, lies beneath the enamel. Dentine surrounds a central cavity of the tooth, filled with nerves and blood vessels. The gums (gingivae) bridge the gap between the tooth and bone. Tooth sockets are lined with a periodontal ligament and elastic con- nective tissue, which both anchor the tooth and act as a shock absorber. FLUORIDE is incorporated into teeth during their formation in the first years of life. Fluoride enters the mineral structure, increasing its resistance to microbial degradation. Fluoride has its greatest effect before and during the emergence of teeth, and it is recommended in the diet until all teeth are in place. Fluoride has been recommended in drinking water up to a concentration of 1 mg per milli- liter as a supplement during tooth formation. Most adults over 50 exhibit symptoms of GIN- GIVITIS (inflamed gums) due to dental plaque accu- mulation. Plaque is the sticky mass of bacterial deposit, which can harden and become tartar. In certain cases, bacterial infection spreads to deep tissues (periodontitis) and can cause tooth and bone loss. Flossing, brushing, and professional cleaning are the foundation for oral health and best defense against plaque formation. Topical application of fluoride as toothpaste or oral antiseptic rinse further reduces tooth decay. (See also PERIODONTAL DISEASE .) tempeh A type of fermented soybean cake and a meat substitute. Tempeh is a food staple in Indone- sia, New Guinea, and, to a lesser degree, in Malaysia. Soaked soybeans are boiled, usually with grains, then fermented (aged) with a mold, Rhizo- pus oligosporus. Mold growth forms a mat around the cooked beans that binds the mixture into a firm cake, which can be fried, baked, roasted, or diced and served in soups. Tempeh contains somewhat more protein than soybean curd ( TOFU). teratogen An agent that causes BIRTH DEFECTS. The placenta acts as a barrier to many potentially damaging substances in maternal blood. However, 616 teeth a number of fat-soluble compounds and drugs can penetrate the placenta and can damage the embryo or fetus. In the United States alone nearly 150,000 infants are born with malformations and develop- mental defects that require medical treatment. About 60 percent of all birth defects have an unknown cause. The other 40 percent are caused by either genetic factors or environmental expo- sures, or both. The catalog of teratogenic agents lists all chemicals that have been reported to be teratogenic in humans or in animals. Americans are exposed to approximately 5 million chemicals; 1,600 of these have been tested in lab animals and about 50 percent are known teratogens. A number of these are related to nutrients. Retinoids, a family of lipids related to VITAMIN A, affect the development of body shape, and overdoses can lead to severe mal- formation. Retinoic acid (C 13 cis—retinoic acid), a vitamin A derivative used in skin treatment for severe ACNE, is a human teratogen. Some investi- gators believe that ETHANOL, the alcohol in alcoholic beverages, could be responsible for as much as 20 percent of cases of mental retardation in the United States. About one-third of all children born to alcoholic mothers are affected by FETAL ALCOHOL SYNDROME , a condition characterized by long-term growth retardation, nervous system irregularities, small head size, and facial anomalies. Maternal alcohol consumption during pregnancy is also associated with cleft palate and congenital head defects. Excessive consumption of selenium can cause a condition called selenosis in which very high levels of selenium accumulate in maternal tissues. Animal studies indicate that selenium under these extreme conditions can be a teratogen. A variety of drugs are teratogens. The general recom- mendation is to avoid alcohol and drugs during pregnancy. terpenoid (terpene) A large family of compounds produced by plants and animals that are classified as LIPIDS. Lipids are fat-soluble (hydrophobic) compounds that dissolve oils and organic solvents. Terpenoids are ring structures assembled from acetyl COENZYME A, the activated form of ACETIC ACID derived from the degradation of CARBOHYDRATE and FAT. Terpenoids include a large number of plant and animal materials such as VITAMIN A, VITAMIN D, VITAMIN E, VITAMIN K, CHOLES- TEROL, steroid hormones, BILE salts; plant oils like limonene from oil of LEMON and ORANGE; pinene from turpentine; geraniol from flowers; menthol from PEPPERMINT; zingiberene from oil of GINGER;B- selinene from oil of CELERY; and squalene from fish liver oil. (See also CARBOHYDRATE METABOLISM; FAT METABOLISM ; HORMONE; STEROIDS .) testosterone The predominant male sex HOR- MONE. Testosterone is the major androgenic hormone (hormones that guide the development and maintenance of male organs and secondary male characteristics, including facial hair, male muscula- ture, with widened shoulders and narrowed hips, among others). Testosterone stimulates the accu- mulation of muscle and the maturation of sperm and stimulates bone growth. Testosterone, like other STEROID hormones, is synthesized from CHO- LESTEROL and is secreted by the testicles. Illicit use of synthetic androgens by athletes and body builders has led to increased muscle mass above the level induced by workouts, with often disastrous side effects. In females, testosterone is synthesized by the ovaries and adrenal glands; the blood levels of testosterone in women are about 10 percent of a typical male. The role of androgens in female development is unclear. The effects of excessive male hormones are better documented with increased risk of diabetes, high blood pressure, heart disease, breast cancer, irregular periods and endometrial cancer. (See also ANABOLIC STEROIDS.) tetrahydrofolic acid (THF) The biologically active form of the B vitamin, FOLIC ACID. THF functions as a coenzyme, that is, an enzyme helper. It differs from folic acid because it possesses extra hydrogen atoms and GLUTAMIC ACID units. THF figures predominantly in the transfer of single carbon units. It helps catalyze the synthesis of the amino acid SERINE from the simplest amino acid, GLYCINE; helps catalyze the nitrogen-containing bases, PURINE and THYMINE, which are used as building blocks of genetic material, DNA; and helps catalyze EPINEPHRINE, a stress hormone released by the adrenal gland, among others. (See also COENZYME.) tetrahydrofolic acid 617 texture The sensation produced in the mouth by a food or beverage, often referred to as “mouth feel.” Adjectives such as chewy, sticky, creamy, hard, lumpy, soft, rough, smooth, gritty, crisp, and the like describe food textures. The physical and chemical properties of a food form the basis for acceptance or rejection. Experience teaches associ- ations between certain foods and textures. If food has a texture that differs from expectations it is judged as of lower quality. A rejected food may be stringy, slimy, gritty, greasy, or contain hard to chew pieces or fragments. (See also FOOD PROCESS- ING; TASTE.) texturized vegetable protein (TVP) SOYBEAN protein that has been processed to resemble meat. Protein is isolated from soybeans, chemically treated, combined with additives and further processed to create colored granules, chunks, or strips. TVP is made by cooking soybean flour with other ingredients and extruding the mixture to form hamburger extenders, bacon bits, and the like. Spun forms are made by spinning fibers and adding flavor and color. TVP can be formed to resemble meat, fish, or poultry. Imitation meat products contain many additives to create a desired texture and flavor, including MONOSODIUM GLUTA- MATE, salt, ARTIFICIAL FOOD COLORS, flavors, flavor enhancers, EMULSIFIERS, and various types of VEG- ETABLE OIL. Although low in cholesterol, imitation meat can be a high-fat option because of the added hydrogenated vegetable oil. TVP is an inexpensive, versatile imitation meat used in a large number of manufactured foods, including simulated CHICKEN, simulated HAM- BURGER , simulated HAM and BACON, simulated pep- peroni, and even imitation nuts. Soybean protein finds its way into casseroles, pizza toppings, stews, snacks, other CONVENIENCE FOODS, and institution- alized cooking. The amount used in soy products is up to the discretion of the manufacturer. TVP is considered a safe food additive. (See also IMITATION FOOD ; PROCESSED FOOD.) thermogenesis (nonshivering thermogenesis) The generation of heat by the body in response to cold. Brown fat tissue (adipose tissue) is geared to produce heat. Brown adipose is most predominant in newborn infants and decreases with age. It is much less abundant in the body than white fat, and occurs in only a few regions, especially the back of the neck and the upper back in adults. The amount of brown fat can increase with exposure to low temperatures. Fat cells in brown adipose tissue can switch over to burn fat and produce heat in response to thyroid hormone. Released heat can then warm the body. This response is more promi- nent in babies than in adults. (See also FAT METAB - OLISM ; SPECIFIC DYNAMIC EFFECT.) thiamin (vitamin B 1 ) A water-soluble vitamin and a member of the B complex. Thiamin is essential for the energy production from carbohydrate and fat. The active form (coenzyme), thiamin pyrophosphate, serves as an enzyme helper in the breakdown of glucose (blood sugar) and in the Kreb’s cycle, the central energy-yielding pathway of the body. Thiamin is also required in the PENTOSE phosphate pathway, a sequence of enzymes that converts glucose to the smaller sugars and energy and liberates hydrogen atoms for biosynthesis. These energy-yielding pathways are critical for normal function of peripheral nerves, skeletal muscle and heart muscle, among others. Severe thiamin deficiency causes BERIBERI. Although rare in the United States, this disease occurs all too frequently in malnourished popula- tions in developing nations who rely on white flour and white rice that are not enriched with thiamin. When beriberi affects primarily the nervous system, it is called “dry” beriberi. Degeneration of insulation (myelin sheath) around nerves of the central nervous system occurs, leading to nerve irritation, pain, numbness, and, in extreme cases, paralysis and muscle wasting. Beriberi produces a staggering gait, numbness of legs, and retarded growth. Mental symptoms such as disorientation, hallucinations and depression occur as well. These symptoms usually respond to thiamin supplementation, and thiamin is also important in treating polyneuritis (nerve inflammation) associated with pregnancy and ALCOHOLISM. Thiamin deficiency can masquerade as SENILITY. Alcoholics may exhibit the mental confusion typical of beriberi. Thiamin supplementation alone does not seem to affect 618 texture mental processes and memory if thiamin deficiency is not involved. An alternate course results in “wet” beriberi, seen as problems with the heart and circulation (abnormal heart rhythm, low blood pressure, ele- vated levels of blood lactic acid, edema [water retention] of the legs, heart muscle weakness, and, ultimately, heart failure). This form of beriberi usually responds quickly and dramatically to thiamin supplementation. Requirements The RECOMMENDED DIETARY ALLOWANCE (RDA) for thiamin for men is 1.5 mg and for nonpregnant women 1.1 mg, and based on an allowance of 0.5 mg per 1,000 calories consumed daily. The require- ment increases with pregnancy and lactation. Be- cause of the prevalence of alcoholism in the United States, thiamin deficiency is not uncommon. Symp- toms of moderate deficiency include FATIGUE, apa- thy, nausea, irritability, depression, slowed wound healing, loss of appetite, indigestion, and constipa- tion. Moderate deficiency symptoms can be caused by crash dieting, alcohol abuse, or liver disease. Peo- ple relying on highly processed foods are at risk, for example, elderly people; low-income persons; teenagers relying on sweets, soft drinks, and low- nutrient foods; and pregnant women. Consuming large amounts of sugar as found in sweets and soft drinks increases the need for thiamin. Also at risk are patients on kidney dialysis or who are sustained for long periods by intravenous nutrients. Factors That Increase Thiamin Requirements • Alcohol. Thiamin assimilation is blocked by alcohol consumption. Alcohol use also injures the small intestine and reduces its ability to absorb thiamin. Alcohol decreases thiamin conversion to thiamin pyrophosphate and depletes tissues of this coenzyme. • Thiamin antagonists. Raw SEAFOOD, such as shrimp, carp, herring, mussels, and clams, and YEAST contain thiaminase, an enzyme that degrades thiamin. Eating a large amount of live yeast can reduce thiamin ABSORPTION. Cooking seafood destroys this enzyme. • Heat-stable anti-thiamin factors have been isolated from several sources. Fermented fish contain factors that limit thiamin uptake. Tea, coffee, and even decaffeinated coffee reduce thiamin absorption. • Baking soda. Cooking with baking soda destroys thiamin. • Cigarette smoking. Smoking adversely affects thiamin uptake and use by tissues. • Medications. Antacids and barbiturates may interfere with thiamin uptake. Foods that contain ample thiamin are wheat germ; meats (pork, beef, ham, organ meats); nuts (pecans, peanuts, walnuts); brewer’s yeast; fortified cereals and grain products. Thiamin is used to enrich flour, breads, and cereals, a practice that has eliminated the widespread thiamin deficiency that existed prior to enrichment programs. Heating food and processing destroys this fragile vitamin. The higher the cooking temperature, the greater the loss. However, microwave cooking does not seem to increase thiamin loss. Thiamin is relatively non- toxic. Very high doses rarely lead to headaches, mental instability, irritability or weakness. Some people are allergic to thiamin injections. (See also CARBOHYDRATE METABOLISM.) Brady, J. A. “Thiamin Status, Diuretic Medications, and the Management of Congestive Heart Failure,” Journal of the American Dietetic Association 95 (1995): 541–544. thickening agents (thickeners) Food additives used to modify the consistency of ice cream, yogurt, pudding, soft drinks, soups, salad dressing, and baby food, among other products. They stabi- lize complex mixtures in manufactured foods to prevent a lumpy or watery consistency or crystal- lization or to prevent oils, coloring agents, and nutrients from separating. Many thickeners are naturally occurring polysaccharides ( AGAR, CAR- RAGEENAN, PECTIN, and the like). Chemically modified starches, called “derivatized starches,” cellulose gums, and other chemically modified materials are frequently used for this purpose. (See also GUAR GUM ; GUM; SEAWEED.) thiourea A small sulfur compound analog that occurs in vegetables like TURNIPS and CABBAGE and other cruciferous vegetables. Thiourea inhibits the synthesis of thyroxine (thyroid hormone) and can thiourea 619 cause goiter formation in lab animals. These vegetables nonetheless add considerable nutritional value and variety to the diet. Vegetables high in thiourea theoretically could cause a potential health problem for people with iodine-deficient diets who rely on turnips—not a likely circum- stance in the United States. thirst A craving for WATER. Thirst sensation is caused by cells in the HYPOTHALAMUS, a small region of the brain that controls both drinking and excret- ing water and processes information about the external environment in order to maintain an opti- mal internal environment ( HOMEOSTASIS). Certain cells detect the concentration of SODIUM in the blood. When the concentration increases above 310 to 340 mg per 100 ml (136 to 145 milli-equiv- alents per liter), cells of the thirst center begin to shrink, triggering nerve impulses that evoke the sensation of being thirsty. A 1 percent increase in effective ion concentration (osmolarity) can trigger this response. Intracellular DEHYDRATION can also stimulate thirst. Another nerve center of the hypothalamus triggers the release of ANTIDIURETIC HOR- MONE from the PITUITARY GLAND. This hormone causes the KIDNEYS to decrease urine output, effec- tively conserving water. (See also ELECTROLYTES.) threonine (Thr, L-threonine) A dietary essential AMINO ACID that serves as a building block of PRO- TEIN. Threonine resembles SERINE, which is a simple amino acid that can be synthesized by tissues. Severe threonine deficiency in experimental animals causes neurologic dysfunction and lameness. In addition to being a raw material for protein synthesis, animal studies suggest that threonine stimulates the THYMUS GLAND and supports the IMMUNE SYSTEM. Adults need an estimated 7 mg/kg of body weight per day. Animal protein like meat, fish, poultry, and dairy products are good dietary sources of this amino acid. (See also AMINO ACID METABOLISM .) thrombin The enzyme derived from the serum protein prothrombin that catalyzes the final step in the BLOOD CLOTTING cascade. VITAMIN K is required in the maturation of prothrombin, and hence is indirectly responsible for thrombin formation. Hemorrhagic (bleeding) disease in newborn infants due to inadequate blood clotting may respond to vitamin K supplementation because vitamin K stores are low at birth, and the sterile gut lacks the beneficial bacteria that normally produce vitamin K in adults. Breast milk contains little vitamin K, and the American Academy of Pediatrics recom- mends administration of vitamin K at birth to promote normal thrombin formation and clotting. thrombosis The obstruction of a blood vessel by a blood clot. Detachment of a fixed blood clot (thrombus) produces a traveling blood clot (embo- lus) that can block a vessel at a distant site. Block- ages of arteries feeding the brain lead to STROKES, while blockage of arteries feeding the heart contribute to HEART ATTACKS. (See also ATHEROSCLERO- SIS; CARDIOVASCULAR DISEASE.) thyme (Thymus vulgaris) A fragrant culinary HERB. Thyme was known to Egyptians, Greeks, and Romans and traditionally was used to instill courage. There are many varieties of this plant. Garden thyme is a small bushy perennial. Thyme is a powerful herb with a distinctive aroma. It can be mixed with PARSLEY and bay leaves as a seasoning, and is used in marinades and sauces. It is used spar- ingly with veal, pork, poultry and poultry stuffing, vegetable soups, chowders, summer squash, and gumbo dishes. Thyme is also used in custards and jellies. Thyme tea has been used in folk medicine for coughs, colds, and sore throats. It has antibacte- rial properties and can boost the immune system. Thyme possesses powerful antifungal properties. (See also SAGE.) thymine A nitrogen-containing base that functions as raw material for DNA. Thymine is easily made by the body and is not a dietary necessity. However, synthesis of thymine requires FOLIC ACID, a B vitamin. Thymine consists of a six-membered ring containing four nitrogen atoms and two carbon atoms. Thymine and other bases of DNA contribute to the unique properties of DNA. DNA exists as two parallel chains linked side by side as a helix. This association relies on a linkage of bases between the two strands; thus thymine in one DNA chain binds to a base called ADENINE on the 620 thirst adjacent chain. It is this specificity of base-pairing that underlies the genetic code and DNA replica- tion during cell division. Thymine is readily broken down by the body and does not yield URIC ACID,a general waste product of DNA and RNA degradation. (See also PURINE; PYRIMIDINE.) thymus gland A component of the IMMUNE SYS- TEM that produces HORMONES to support the development of the immune cells. The thymic hormones include thymosin, thymic humoral factor, thymic factor, and thymopoietin. Together they promote the proliferation and maturation of various types of T cells, lymphocytes (white blood cells) that help defend the body against foreign invaders. Helper T cells (which activate other lymphocytes), cytotoxic T cells (which attack cells) and suppressor T cells (which limit lymphocyte activity) represent the major class of T cells. The thymus shrinks as people age. At birth, thymic tissue represents 0.4 percent of body weight. At the age of 70, the thymus accounts for only 0.0007 percent. This atrophy correlates with a gradual weakening of the immune system. Orally administered extracts of beef thymus have been used to support the function of the thymus gland. Antioxidants like VITAMIN C, VITAMIN E, BETA- CAROTENE , and SELENIUM are nutrients that enhance T-cell function and may retard thymic shrinkage because the gland is susceptible to oxidative damage. The amino acids ORNITHINE and ARGININE can also stimulate the thymus gland. ZINC, VITAMIN B 6 , and vitamin C seem crucial to support thymic hormone production and cell-dependent immune function. Echinacea angustifolia and licorice enhance immune function performed by the thymus gland. Thymic factors are being studied as therapeutic agents for AIDS patients and cancer patients. (See also AGING; ENDOCRINE SYSTEM.) thyroid gland The gland responsible for the formation of thyroid HORMONES and calcitonin. The most plentiful thyroid hormone is thyroxine (T4), which is converted to triiodothyronine (T3), which is more potent but is present in smaller amounts in the blood. This conversion takes place in the liver and lungs. Thyroxine consists of the amino acid TYROSINE, to which iodine is bound. Tyrosine is a building block of the protein thyroglobulin, to which IODINE is added during its processing. Thy- roxine is released from thyroglobulin when the thyroid gland is stimulated, for instance, by other hormone signals. T3 and T4 increase the rate of oxygen uptake, the rate of oxidation of fat and carbohydrate for ENERGY , and the BASAL METABOLIC RATE, the rate at which energy maintains body function. Thyroid hormones also increase carbohydrate uptake by the intestine; regulate lipid metabolism; help regulate normal growth, brain development, and skeletal maturation in children; and help regulate the central nervous system as well as the function of peripheral nerves. In children, thyroid hormones help regulate growth and development by working together with GROWTH HORMONE. Furthermore, thyroid hormones regulate the activity of the nervous system, which in turn increases blood flow, increases heartbeat and blood pressure, and increases movement of the gastrointestinal tract ( PERISTALSIS). Calcitonin operates differently. This hormone lowers the level of CALCIUM and phosphate in the blood by inhibiting BONE breakdown (demineral- ization) and by increasing calcium and phosphate incorporation into bones. This appears to take place by inhibiting bone-destroying cells called osteo- clasts. The HYPOTHALAMUS regulates the activity of the thyroid gland. This portion of the brain regulates responses to changes in blood chemistry such as lowered blood sugar and decreased body temperature. It releases a hormone called thyrotropin releasing hormone which stimulates the pituitary to secrete thyroid stimulating hormone (TSH) into the bloodstream. In turn, TSH then stimulates the thyroid gland to release its hormones to speed up metabolism. In decreased thyroid gland function ( HYPOTHY- ROIDISM), body temperature decreases, reaction time is decreased and thought processes are slowed. Low basal temperature, depression, FATIGUE, dry skin, dry hair, low blood pressure and difficulty in losing weight also characterize hypothyroidism. In extreme cases, a GOITER develops (enlarged thyroid gland). Iodine, ZINC, VITAMIN E and VITAMIN A, RIBOFLAVIN, NIACIN, VITAMIN B 6 , and vitamin C are required for the formation of thyroid hormone. Exercise stimu- thyroid gland 621 [...]... the throat The upper surface of the tongue is covered by small projections called papillae TASTE buds are located MOUTH 624 tooth on the papillae; they are responsible for the sense of taste Taste receptors located at the tip of the tongue are most responsive to sweet and salty foods but respond to sour and bitter-tasting substances as well The taste buds along the sides of the tongue respond to sour... vegetable oils firmer and more spreadable During the process, some of the unsaturated fatty acids are flipped from their bent shape to a straightened form, called transferrin 627 trans-fatty acids The resulting trans-fat possesses many properties of saturated fats Trans-fatty acids possess higher melting points than unaltered unsaturates and are solids at room temperature The trans-fatty acid content of. .. shortening represent other major sources of trans-fatty acids in the American diet Low levels of trans-fatty acids are a normal part of the diet However, the U.S diet typically provides 20 times the intake of trans-fatty acids obtained from natural sources Estimates of trans-fat intake range from 8 g to 20 g per day, reflecting an increased consumption of vegetable fat and processed foods Trans-fatty... Self-basting turkeys contain much more fat than unbasted birds, and often the injected fat is saturated (butter or coconut oil) Ground turkey combines both white and dark meat and may include fat and skin The amounts of skin and fat vary because there are no of cial standards for fat content for ground turkey The food label may indicate the percentage of fat content: Supermarkets may provide products listed... recommended that pregnant women eat no more than two cans of tuna a week If they eat other fish, they should limit consumption to just one can of tuna Ninety-five percent of tuna that is consumed in the United States is canned Canned tuna in oil is a high-calorie food Oil-packed tuna contains 23 g of fat and 1,400 calories per 3-oz serving, while water-packed tuna contains 1 g of fat and a total of 135 calories... Trans-fatty fats do not substitute for ESSENTIAL FATTY ACIDS, and they may worsen symptoms of essential fatty acid deficiency They seem to antagonize the conversion of essential fatty acids to PROSTAGLANDINS, hormone-like lipids that regulate pain, smooth muscle contraction, raise or lower blood pressure depending on the type, and perform many other functions Diets that incorporate high levels of trans-fatty acid... with high trans-fatty acid consumption The National Academy of Sciences concluded that currently consumed levels of trans-fatty acids are safe because small amounts are consumed Food labels will soon indicate the amount of trans-fatty acids in a food Until then, when a food label lists the amount of unsaturated (monounsaturated and polyunsaturated fat), it cannot include trans-fats When a product label... cocktails are usually tomato-based Fresh tomatoes are a good source of VITAMIN C, although the vitamin C content varies with the time of year Because the consumption is so high, tomatoes are a major dietary source of vitamin C in the United States Tomatoes also provide betacarotene, although their intense orange-red color is due to another carotenoid called LYCOPENE, which lacks vitamin A activity Lycopene... unsaturated fatty acids Synthetic triglycerides can contain a single type of fatty acid; in this case, the triglyceride is named after the fatty acid, e.g., tripalmitin contains only PALMITIC ACID (a fatty acid with 16 carbon atoms) and tristearin contains only STEARIC ACID (a fatty acid with 18 carbon atoms) MEDIUM-CHAIN TRIGLYCERIDES occur in COCONUT OIL and palm kernel oil and BUTTER They contain shorter... five to seven months of age Grading by the USDA is voluntary Unlike the grading of red meat, poultry grading is based on appearance, not fat content Graded birds should be free of feathers and blemishes Turkey meat is lower in fat than most red meat, and brown meat contains more fat than light meat Almost all of the fat lies under the skin and can be trimmed off White meat, without skin, is a low-fat . papillae; they are responsible for the sense of taste. Taste receptors located at the tip of the tongue are most responsive to sweet and salty foods but respond to sour and bitter-tasting substances. of trans-fatty acids are a normal part of the diet. How- ever, the U.S. diet typically provides 20 times the intake of trans-fatty acids obtained from natural sources. Estimates of trans-fat intake. and the maturation of sperm and stimulates bone growth. Testosterone, like other STEROID hormones, is synthesized from CHO- LESTEROL and is secreted by the testicles. Illicit use of synthetic androgens

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