The Encyclopedia Of Nutrition And Good Health - T ppsx

Taro leaves should not tuber-bear-be consumed raw tuber-bear-because some varieties containhigh levels of OXALIC ACID calcium oxalate thatcan be toxic when large amounts are consumed.Tar

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

pro-duction 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

con-tains little vitamin B12activity

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 thatfruit’s flavor and sweetness They are generally eas-ier to peel and eat because the skin is somewhatloose around the pulpy flesh The fruit has existedfor several thousand years, probably originating inSoutheast Asia from an accidental cross-breeding ofmandarin oranges and pomelos (an ancestor of themodern grapefruit) Like other citrus fruits, tangelosare 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 ORANGEand nated in China The fruit has a thin, easily peeledskin and segments separate readily Unlike oranges,which can be stored at room temperature for severalweeks, tangerines need to be refrigerated if keptlonger than a couple of days They are eaten raw orused in fruit or gelatin-based salads Tangerines pro-vide less vitamin C than oranges The edible portion

origi-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; thi-amin, 0.09 mg; riboflavin, 0.02 mg; niacin, 0.13 mg

tannins A family of complex compounds thatoccur in the bark or leaves of certain plants andtrees Tannins are classified chemically asflavonoids they are composed of two or more aro-matic ring structures that act as antioxidants toquench oxidative damage due to FREE RADICALS.Polyphenols block the ability of certain compounds

to cause mutations in test tube experiments andinhibit lung and skin tumors in experimental ani-mals 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

CHOCOLATEmay 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 GLUCOSEand 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

pud-dings Like most starches, tapioca swells and

thick-ens when cooked in water It is often used to

thicken soups, pies, and puddings High-grade

tapi-oca 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;

car-bohydrate, 28.2 g; fat, 8.4 g; sodium, 257 mg;

cal-cium, 173 mg; thiamin, 0.07 mg; riboflavin, 0.30

mg; niacin, 0.2 mg (See also FLOUR.)

tardive dyskinesia A disabling disorder

some-times 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

nutri-ent CHOLINEand of LECITHIN, the PHOSPHOLIPIDfrom

which choline is derived, reduce the abnormalmovements of tardive dyskinesia, and lecithinremains an important treatment option TRYPTO-

PHAN, together with NIACINAMIDE and VITAMIN B6,may relieve symptoms of tardive dyskinesia Large-scale studies have suggested that patients who sup-plement with NIACIN, MANGANESE, and ZINC

concomitantly with drug treatment experiencedecreased symptoms of tardive dyskinesia TheAmerican Psychiatric Association concluded (1991)that the general clinical value of such nutrientsshould be confirmed with long-term, large-scalestudies before acceptance Preliminary clinicalstudies suggest that VITAMIN Emay also decrease theseverity 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, ing plant native to Southeast Asia Taro cultivationgradually spread to Japan, China, the easternMediterranean region, Polynesia, New Zealand,West Africa, and South America Taro root is ahigh-carbohydrate food Poi, a staple food of Poly-nesia, is made from the taro root A common vari-ety of taro produces a brown-skinned root with apale purple or white flesh Taro root is sold in Asianmarkets and specialty shops Taro leaves should not

tuber-bear-be consumed raw tuber-bear-because some varieties containhigh levels of OXALIC ACID (calcium oxalate) thatcan be toxic when large amounts are consumed.Taro root can be used like potatoes; it is boiled,baked, or steamed The vegetable becomes verysticky upon cooling The tuber has a nutrient valuesimilar to the Irish POTATO

tarragon (Artemesia dracunculus) A smallperennial 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 ragon is used fresh or dried to create a somewhatanise-like flavor in chicken, veal, and turkey

Tar-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

pro-duction 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

addi-tive (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

typ-ical “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 FDArequired 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 2,000taste buds located chiefly on the tongue Theyoccur also on the soft palate and in the throat Typ-ically, taste buds occur in small protuberancescalled papillae, which give the upper surface of thetongue a rough appearance Taste buds possessexternal cells with hair-like extensions that projectthrough a central taste pore When a dissolved sub-stance enters a taste pore and contacts the hair-likeprojections, it can generate a nerve impulse that isrelayed to the brain

Of all the seemingly endless different flavors andsubtle tastes, there are only four basic taste sensa-tions: sweet, sour, salt, and bitter Most other tastesare combinations of these modified by odors.When a person has a cold, the olfactory sensations(SMELL) do not operate normally, although thetaste sensations may be normal The olfactory sys-tem (sense of smell) is much more sensitive tostimulation than the gustatory system for a givenconcentration of a substance

Taste buds located in different areas possess ferent sensitivities to taste sensations Thus, the tip

dif-of the tongue reacts with all primary taste tions, but it is highly sensitive to salty and sweetmaterials The edges of the tongue respond morereadily to sour substances, while the back of thetongue responds most to bitter substances

sensa-Foods that taste bitter are generally rejected.This may be part of a protective mechanism inhuman evolution, because many poisonous plantscontain toxic substances that produce a bitter taste

A degree of saltiness is often considered pleasantbut very salty foods will be rejected The preferencefor salty foods in most people is acquired Gradu-ally, reducing the amount of salt in foods willuncover the subtle, rich flavors of minimallyprocessed foods Sweet tasting foods create pleasur-able feelings ARTIFICIAL SWEETENERS have beendeveloped that will trigger the sweet receptorswithout contributing calories A sour taste may beeither objectionable or desirable Dilute acid solu-tions such as VINEGAR can create tangy, zestfulfoods and beverages, while excessive acidity is notpalatable The taste threshold varies for each pri-mary taste Bitter substances possess the lowesttaste threshold, that is, they can be distinguished atlow 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 ZINCdeficiency 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

sup-ports 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

metab-olism of the brain

The body possesses a limited capacity to produce

taurine, and certain individuals may require

dietary taurine, depending on their nutritional

sta-tus Pre-term and full-term infants do not

synthe-size appreciable taurine, which is the most

abundant amino acid in breast milk With time thetaurine content of breast milk declines as the infantgrows and begins to manufacture taurine Taurinewas once omitted from infant formulas; now it isadded routinely Taurine is concentrated in animalprotein, 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 Itsuse is considered experimental (See also METHIO-

NINE; NERVOUS SYSTEM.)

tea (Camellia sinensis) The dried leaves of a cal 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 theleading tea growing countries Flower, leaf, bark,roots, and seeds of various plants are used in herbal

tropi-teas but these are not derived from Camellia sinensis.

Differences in color and aroma among varioustypes of tea reflect primarily differences in tea pro-cessing Nearly 75 percent of tea ends up as blacktea, in which leaves are crushed to release enzymesthat oxidize substances in leaves (polyphenols) thatcreate the rich flavor The leaves are then dried inhot air to develop a brown/black color For greentea, fresh leaves are steamed to destroy the oxidiz-ing enzymes, then rolled and dried Instant tea wasdeveloped in the United States in 1948 It is pre-pared by brewing a strong tea and removing water

to leave a dried concentrate, which can be added towater Oolong tea is partially fermented to create agreen-brown leaf

Brewed tea is prepared by pouring boiling waterover dried tea leaves Generally, the best flavor isobtained when tea has steeped (soaked) in boiledwater for up to five minutes for black tea, one totwo minutes for green tea Longer steeping createstea with more TANNIN and increased bitterness.Black tea, and to a lesser extent, green tea bind ironbecause of the tannin content Tannins contribute

to the pungency of tea Tea is a mild stimulantbecause it contains CAFFEINE A cup of black teaprovides 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

vit-amin C; on the average, one cup of green tea

pro-vides as much vitamin C as half a cup of orange

juice Tea also contains tannin and catechin

(classi-fied 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 ANTIOXIDANTproperties

Epigallocate-chin is the most potent cateEpigallocate-chin 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,

peo-ple 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

bacte-ria, and inhibit flu virus and boost the immune

sys-tem 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 theenamel, the hardest part of the tooth This protec-tive layer resists the wear of chewing and theaction of bacteria A hardened type of bone coversthe roots Dentine, a hard, mineralized layer, liesbeneath the enamel Dentine surrounds a centralcavity of the tooth, filled with nerves and bloodvessels The gums (gingivae) bridge the gapbetween the tooth and bone Tooth sockets arelined with a periodontal ligament and elastic con-nective tissue, which both anchor the tooth and act

as a shock absorber

FLUORIDEis incorporated into teeth during theirformation in the first years of life Fluoride entersthe mineral structure, increasing its resistance tomicrobial degradation Fluoride has its greatesteffect 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 ing 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-

drink-GIVITIS(inflamed gums) due to dental plaque mulation Plaque is the sticky mass of bacterialdeposit, which can harden and become tartar Incertain cases, bacterial infection spreads to deep tis-sues (periodontitis) and can cause tooth and boneloss Flossing, brushing, and professional cleaningare the foundation for oral health and best defenseagainst plaque formation Topical application offluoride as toothpaste or oral antiseptic rinse fur-ther reduces tooth decay (See also PERIODONTAL DISEASE.)

accu-tempeh A type of fermented soybean cake and ameat substitute Tempeh is a food staple in Indone-sia, New Guinea, and, to a lesser degree, inMalaysia 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 firmcake, which can be fried, baked, roasted, or dicedand served in soups Tempeh contains somewhatmore protein than soybean curd (TOFU)

teratogen An agent that causes BIRTH DEFECTS.The placenta acts as a barrier to many potentiallydamaging 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

chemi-cals 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

per-cent 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 (C13cis—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

alco-holic 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

tis-sues 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

com-pounds 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 ACIDderived 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 likelimonene from oil of LEMON and ORANGE; pinenefrom turpentine; geraniol from flowers; mentholfrom PEPPERMINT; zingiberene from oil of GINGER; B-selinene from oil of CELERY; and squalene from fishliver oil (See also CARBOHYDRATE METABOLISM; FAT METABOLISM; HORMONE; STEROIDS.)

testosterone The predominant male sex HOR

-MONE Testosterone is the major androgenic mone (hormones that guide the development andmaintenance of male organs and secondary malecharacteristics, 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 spermand stimulates bone growth Testosterone, likeother STEROIDhormones, is synthesized from CHO-

hor-LESTEROLand is secreted by the testicles Illicit use

of synthetic androgens by athletes and bodybuilders has led to increased muscle mass above thelevel induced by workouts, with often disastrousside effects

In females, testosterone is synthesized by theovaries and adrenal glands; the blood levels oftestosterone in women are about 10 percent of atypical male The role of androgens in femaledevelopment is unclear The effects of excessivemale hormones are better documented withincreased risk of diabetes, high blood pressure,heart disease, breast cancer, irregular periods andendometrial cancer (See also ANABOLIC STEROIDS.)

tetrahydrofolic acid (THF) The biologicallyactive form of the B vitamin, FOLIC ACID THF func-tions as a coenzyme, that is, an enzyme helper Itdiffers from folic acid because it possesses extrahydrogen atoms and GLUTAMIC ACID units THF figures predominantly in the transfer of single car-bon units It helps catalyze the synthesis of theamino acid SERINE from the simplest amino acid,

GLYCINE; helps catalyze the nitrogen-containingbases, PURINEand THYMINE, which are used as build-ing blocks of genetic material, DNA; and helps cat-alyze EPINEPHRINE, a stress hormone released by theadrenal 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 HAMand 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

pro-duce heat Brown adipose is most predominant innewborn infants and decreases with age It is muchless abundant in the body than white fat, andoccurs in only a few regions, especially the back ofthe neck and the upper back in adults The amount

of brown fat can increase with exposure to lowtemperatures Fat cells in brown adipose tissue canswitch over to burn fat and produce heat inresponse to thyroid hormone Released heat canthen 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 vitaminand a member of the B complex Thiamin is essen-tial for the energy production from carbohydrateand fat The active form (coenzyme), thiaminpyrophosphate, serves as an enzyme helper in thebreakdown of glucose (blood sugar) and in theKreb’s cycle, the central energy-yielding pathway

of the body Thiamin is also required in the PENTOSE

phosphate pathway, a sequence of enzymes thatconverts glucose to the smaller sugars and energyand liberates hydrogen atoms for biosynthesis.These energy-yielding pathways are critical fornormal function of peripheral nerves, skeletal mus-cle and heart muscle, among others

Severe thiamin deficiency causes BERIBERI.Although rare in the United States, this diseaseoccurs all too frequently in malnourished popula-tions in developing nations who rely on white flourand white rice that are not enriched with thiamin.When beriberi affects primarily the nervous sys-tem, it is called “dry” beriberi Degeneration ofinsulation (myelin sheath) around nerves of thecentral nervous system occurs, leading to nerveirritation, pain, numbness, and, in extreme cases,paralysis and muscle wasting Beriberi produces astaggering gait, numbness of legs, and retardedgrowth Mental symptoms such as disorientation,hallucinations and depression occur as well Thesesymptoms usually respond to thiamin supplemen-tation, and thiamin is also important in treatingpolyneuritis (nerve inflammation) associated withpregnancy and ALCOHOLISM Thiamin deficiencycan masquerade as SENILITY Alcoholics may exhibitthe mental confusion typical of beriberi Thiaminsupplementation 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

usu-ally responds quickly and dramaticusu-ally 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

con-version 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

iso-lated from several sources Fermented fish

con-tain factors that limit thiamin uptake Tea,

coffee, and even decaffeinated coffee reduce amin absorption

thi-• Baking soda Cooking with baking soda destroysthiamin

• Cigarette smoking Smoking adversely affectsthiamin uptake and use by tissues

• Medications Antacids and barbiturates mayinterfere with thiamin uptake

Foods that contain ample thiamin are wheatgerm; meats (pork, beef, ham, organ meats); nuts(pecans, peanuts, walnuts); brewer’s yeast; fortifiedcereals and grain products Thiamin is used toenrich flour, breads, and cereals, a practice that haseliminated the widespread thiamin deficiency thatexisted prior to enrichment programs Heating foodand processing destroys this fragile vitamin Thehigher the cooking temperature, the greater theloss However, microwave cooking does not seem

to increase thiamin loss Thiamin is relatively toxic Very high doses rarely lead to headaches,mental instability, irritability or weakness Somepeople are allergic to thiamin injections (See also

non-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 additivesused 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 toprevent a lumpy or watery consistency or crystal-lization or to prevent oils, coloring agents, andnutrients from separating Many thickeners arenaturally occurring polysaccharides (AGAR, CAR-

RAGEENAN, PECTIN, and the like) Chemically fied starches, called “derivatized starches,” cellulosegums, and other chemically modified materials arefrequently used for this purpose (See also GUAR GUM; GUM; SEAWEED.)

modi-thiourea A small sulfur compound analog thatoccurs in vegetables like TURNIPSand CABBAGEandother cruciferous vegetables Thiourea inhibits thesynthesis of thyroxine (thyroid hormone) and can

thiourea 619

cause goiter formation in lab animals These

veg-etables 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

hypo-thalamus triggers the release of ANTIDIURETIC HOR

-MONE from the PITUITARY GLAND This hormone

causes the KIDNEYSto decrease urine output,

effec-tively conserving water (See also ELECTROLYTES.)

threonine (Thr, L-threonine) A dietary essential

AMINO ACIDthat 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

ani-mals 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 CLOTTINGcascade VITAMIN Kis required

in the maturation of prothrombin, and hence is

indirectly responsible for thrombin formation

Hemorrhagic (bleeding) disease in newborn infantsdue to inadequate blood clotting may respond tovitamin K supplementation because vitamin Kstores are low at birth, and the sterile gut lacks thebeneficial 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 pro-mote 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 con-tribute to HEART ATTACKS (See also ATHEROSCLERO-

SIS; CARDIOVASCULAR DISEASE.)

thyme (Thymus vulgaris) A fragrant culinary

HERB Thyme was known to Egyptians, Greeks, andRomans and traditionally was used to instillcourage 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 bemixed with PARSLEYand 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, andgumbo dishes Thyme is also used in custards andjellies Thyme tea has been used in folk medicinefor 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 tions as raw material for DNA Thymine is easilymade by the body and is not a dietary necessity.However, synthesis of thymine requires FOLIC ACID,

func-a B vitfunc-amin Thymine consists of func-a six-memberedring containing four nitrogen atoms and two car-bon atoms Thymine and other bases of DNA con-tribute to the unique properties of DNA DNAexists as two parallel chains linked side by side as ahelix This association relies on a linkage of basesbetween the two strands; thus thymine in oneDNA chain binds to a base called ADENINEon 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

degrada-tion (See also PURINE; PYRIMIDINE.)

thymus gland A component of the IMMUNE SYS

-TEMthat produces HORMONESto support the

devel-opment 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 SELENIUMare nutrients that enhance

T-cell function and may retard thymic shrinkage

because the gland is susceptible to oxidative

dam-age The amino acids ORNITHINE and ARGININE can

also stimulate the thymus gland ZINC, VITAMIN B6,

and vitamin C seem crucial to support thymic

hor-mone 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

for-mation 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, towhich IODINE is added during its processing Thy-roxine is released from thyroglobulin when thethyroid gland is stimulated, for instance, by otherhormone 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 atwhich energy maintains body function Thyroidhormones also increase carbohydrate uptake by theintestine; regulate lipid metabolism; help regulatenormal growth, brain development, and skeletalmaturation in children; and help regulate the cen-tral nervous system as well as the function ofperipheral nerves In children, thyroid hormoneshelp regulate growth and development by workingtogether with GROWTH HORMONE Furthermore,thyroid hormones regulate the activity of the ner-vous system, which in turn increases blood flow,increases heartbeat and blood pressure, andincreases movement of the gastrointestinal tract(PERISTALSIS)

Calcitonin operates differently This hormonelowers the level of CALCIUMand phosphate in theblood by inhibiting BONE breakdown (demineral-ization) and by increasing calcium and phosphateincorporation into bones This appears to take place

by inhibiting bone-destroying cells called clasts

osteo-The HYPOTHALAMUS regulates the activity of thethyroid gland This portion of the brain regulatesresponses to changes in blood chemistry such aslowered blood sugar and decreased body tempera-ture It releases a hormone called thyrotropinreleasing hormone which stimulates the pituitary

to secrete thyroid stimulating hormone (TSH) intothe bloodstream In turn, TSH then stimulates thethyroid gland to release its hormones to speed upmetabolism

In decreased thyroid gland function (HYPOTHY

-ROIDISM), body temperature decreases, reaction time

is decreased and thought processes are slowed Lowbasal temperature, depression, FATIGUE, dry skin, dryhair, low blood pressure and difficulty in losingweight also characterize hypothyroidism In extremecases, a GOITER develops (enlarged thyroid gland).Iodine, ZINC, VITAMIN E and VITAMIN A, RIBOFLAVIN,

NIACIN, VITAMIN B6, and vitamin C are required forthe formation of thyroid hormone Exercise stimu-

thyroid gland 621

lates the thyroid gland On the other hand, an

over-active thyroid gland (hyperthyroidism) is

character-ized by a high metabolic rate, nervousness, weight

loss, heat intolerance, excessive sweating, and

increased heart rate This metabolic disorder can

mimic IRRITABLE BOWEL SYNDROME (See also CATAB

-OLISM; ENDOCRINE SYSTEM.)

Weetman, A P “Graves’ Disease,” New England Journal of

Medicine 343, no 17 (2000): 1,236–1,248.

tin A heavy metal There is weak evidence that it

is a required nutrient in animals, although it has no

known metabolic function Rigorous exclusion of

tin from diets of laboratory animals impaired

reproduction and caused other abnormal growth If

it functions as a nutrient in humans, typical daily

ingestion of 1.5 to 5 mg per day more than meets

requirements Tin is used to line certain cans, and

acidic foods like canned PINEAPPLE and canned

TOMATOES can leach out tin from the inside of a

can However, there is little evidence to indicate

that tin can be toxic (See also HEAVY METALS.)

tissue A level of cellular organization in which

groups of similar cells perform similar functions

Cells of tissues adhere to each other through

inter-cellular materials (connective tissue) and tight

bonding (tight junctions) The epithelial tissue of

the intestine is representative of this layer of cells

and contains mucus-secreting cells and

enzyme-secreting cells Other tissues include nervous tissue,

muscle tissue, connective tissue, and ADIPOSE TIS

-SUE Nerve tissue is composed of nerve cells

(neu-rons) and their supporting cell types (neuroglial

cells) Muscle tissue contains muscle fibers

assem-bled from muscle cells (myoblasts) Connective

tis-sue contains fibroblasts, cells that secrete materials

from an extracellular matrix, including the

struc-tural protein, COLLAGEN, together with GLYCOSA

-MINOGLYCANS (MUCOPOLYSACCHARIDES), consisting

of long chains of modified sugars

Mucopolysac-charides absorb water and are slippery They form

a gel-like environment for connective tissue cells

called ground substance Adipose tissue is fatty

connective tissue that contains fat cells (ADI

-POCYTES) Reticular tissue is a fibrous connective

tissue that forms the support for internal organs

like the liver, spleen, lymph glands, and lungs (Seealso BONE; SKIN.)

tocopherol See VITAMIN E

tocotrienols Members of the vitamin E family.The four tocotrienols—alpha, beta, gamma, anddelta—are one of the two families of compoundsthat make up what experts call vitamin E Theother family is tocopherols, which are more com-mon in the diet Preliminary research has revealedthat tocotrienols’ ANTIOXIDANT properties showpromise in treating a variety of illnesses includingcancer, cardiovascular disease, and memory deteri-oration associated with aging Tocotrienols arefound in most vegetable oils

Packer, L et al “Molecular Aspects of alpha Tocotrienol

Antioxidant Action and Cell Signaling,” Journal of

Nutrition 131 (2001): 369S–373S.

tofu A SOYBEANcurd prepared by coagulations ofthe PROTEINin soybean milk with calcium or mag-nesium salts Tofu is a white semisolid containing

88 percent water, 6 percent protein, and 3 percentfat It is shaped into blocks and kept moistenedand refrigerated in plastic tubs In much of Asia,tofu is the most common soy-based food Tofuappears as deep-fried cakes, pouches, and puffs;tofu pudding; fermented tofu (bean curd cheese);tofu burgers and grilled tofu; bean curd sheets(dried yuba); Chinese-style pressed tofu; andsavory pressed tofu Tofu offers a number ofadvantages as a protein source Soy protein is ahigh-quality protein, approaching the value of

MEAT because it is rich in essential amino acids.Furthermore, soy protein is inexpensive and con-tains no CHOLESTEROL Tofu supplies CALCIUMwhensoy milk is coagulated with lime Such tofu con-tains 130 mg of calcium per 3.5-oz serving, a sub-stantial part of the daily calcium requirement (Iftofu is prepared with magnesium, the calciumcontent is negligible.) Nutrient content of onepiece of tofu measuring two in by three in by one

in (120 g) is: 86 calories; protein, 9.4 g; drate, 2.9 g; fiber, 2.2 g; fat, 5 g; calcium, 108 mg;iron, 2.2 mg; thiamin, 0.18 mg; riboflavin, 0.08mg; niacin, 0.1 mg

carbohy-622 tin