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These findings led Dr. Bartoshuk and her colleagues to begin studying food preferences with regard to taste genetics. While all humans are born with an innate liking for sweets, she said, supertasters find many sugary foods to be sickeningly sweet. Frosting is yucky. Saccharine has a strong aftertaste. Coffee is too bitter, and alcohol too sharp. Hot peppers and ginger produce an unpleasant burn. Food should be tepid.

Supertasters are sensitive to fats, said Dr. Valerie Duffy, a registered dietitian at the University of Connecticut in Storrs. Taste buds do not react to any flavor of fat, but they react to its touch, sending that information through the trigeminal nerve. Fat molecules literally press against the taste buds, producing a tactile sensation that is interpreted by the brain as viscous, slippery or greasy, she said.

In an experiment, Dr. Duffy asked people to taste different milk samples -- skimmed, 1 percent fat, 2 percent fat, 4 percent fat, half and half, heavy cream and cream with oil added. Nontasters could not tell the difference between skim milk and the heavy creams, she said. Supertasters were extremely sensitive to gradations in fat. As fat content increased, they perceived more creaminess.

''If you go through life as a nontaster,'' Dr. Duffy said, ''it takes more to get the flavor out of food than it does for a supertaster.''

''The world is built for regular tasters,'' Dr. Bartoshuk said. For them, most foods are not too sweet, bitter, salty or sour. And their diets may be healthier because of it.

Dr. Drewnowski has found that supertasters tend not to like the strong tastes of many fruits and vegetables, which are the main sources of flavinoids, isothiocyanates and other cancer-preventing agents. PROP tasters do not like grapefruit juice, and many even find orange juice unpleasant, he said.

But foods like broccoli, which many supertasters do not like, can be cooked in ways that blunt the bitter undertaste, Dr. Drewnowski said. Asians tend to be supertasters, yet they eat a mainly vegetarian diet, often stir-fried dishes with oils and other flavors mixed in. Raw cruciferous vegetables are not a mainstay of Chinese cuisine.

However food is cooked, one's PROP status may play a role in weight control, said Dr. Laurie Lucchina, a postdoctoral student in Dr. Bartoshuk's laboratory. A small study of older women found that supertasters tend to be thinner than nontasters and have serum lipid values associated with lower cardiovascular risk.

That makes sense, Dr. Lucchina said. Supertasters tend to eschew sugary, fatty foods throughout their lives. Preliminary data suggests that the same holds true for younger women.

At the same time, sensitivity to PROP tends to decline with age, Dr. Lucchina said, suggesting that hormones play a role in taste physiology. After menopause, women who are supertasters tend to be less sensitive to bitter foods.

Studies now under way suggest that monthly estrogen fluctuations alter PROP sensations in younger women so that the sense of bitterness in foods varies throughout each month, Dr. Bartoshuk said. And during the first trimester of pregnancy, even nontaster and medium-taster women find many previously acceptable foods, like coffee, to be suddenly unpalatable.

That makes evolutionary sense, Dr. Bartoshuk said. Bitterness often predicts toxicity. Pregnant women are good poison detectors because their tastes are designed to protect the developing fetus.

Morning sickness would therefore not be an accidental misery that just has to be put up with, but a way of avoiding harmful foods -- a useful, if troublesome, gift of natural selection.

Diagram: ''A Matter of Taste: How Genes Affect Preferences'' Researchers find that a quarter of people are supertasters, who react violently to a bitter test of chemical; half are medium tasters, a quarter nontasters. Genetics seems to determine characteristics of tastings apparatus. Pores on papillae on tip of tongue are conduits for taste stimuli to reach taste buds. Supertaster: Supertasters have many more papillae, very closely arranged, but much smaller. Nontaster: Nontasters have many fewer papillae, with far fewer pores, though they are larger. (Sources: Dr. Linda Bartoshuk, Dr. Valerie Duffy and Dr. Laurie Lucchina; The A.M.A. Encyclopedia of Medicine $(Random House$))