The case for fruits and vegetables goes beyond the need for vitamin C, iron or beta carotene. Scientists are just beginning to grasp the power of plant substances called phytochemicals--most of which have little or no recognized value as nutrients. These substances hold tremendous promise in the battle against cancer, heart disease and a number of other ailments. The glycyrrhizin in licorice root may protect against prostate cancer; eat enough garlic, and your blood pressure should go down.

Research has barely begun on a handful of the 500 or so known phytochemicals. Already, the lutein in spinach and the selenium in Brazil nuts, which may help ward off cancer by boosting the body's immune response, are available in pill form in some health food stores. But scientists have far to go before they can say which phytochemicals act alone, which act in synergy with other compounds, how much is enough, how much is overdoing it. Researchers agree that it's too soon to trade food for pills.

A single Brazil nut more than covers the U.S. recommended daily allowance for selenium, for example, at less cost than a supplementary pill. And too much of a good thing can be toxic: A steady diet of 100 Brazil nuts a day has been known to have one of the same side effects as chemotherapy: It makes some people's hair fall out. Meanwhile, despite dozens of studies suggesting selenium's cancer-prevention qualities, its powers remain in question. A study in the April 5 Journal of the National Cancer Institute found no anticancer benefit among women with high levels of selenium in their bodies. Broccoli contains a cornucopia of substances that may block carcinogens before they reach their cellular targets. But researchers believe broccoli's best secrets are still undiscovered.

"I think Euclid and I would agree that the whole food is better than the sum of its phytochemicals," says James Duke, a botanist with the U.S. Department of Agriculture whose own diet emphasizes a wide variety of fruits, nuts and vegetables. One favorite recipe is genistein gumbo. (Genistein, a phytochemical in soy products and legumes, has been found to retard cancer growth in test tubes--possibly by inhibiting the new blood vessel growth on which tumors depend.) The gumbo calls for equal parts soybeans, black-eyed peas, fava beans, garbanzos, kidney beans, lentils and lima beans. Soak overnight; boil; then mix in a blender with curry powder, hot pepper sauce and a large onion. Toss in some tofu, season--and enjoy.

GARLIC. Garlic contains allium compounds, which appear to lower blood pressure and cholesterol levels, enhance the immune system and memory, block carcinogens from entering cells and stop malignant changes within cells. Garlic pills have been shown to be beneficial, as has roasted or sauteed garlic, but raw garlic can irritate the gastrointestinal tract.

CITRUS FRUITS. Lemons, limes, oranges and other citrus fruits contain monoterpenes, which may help prevent cancer by hustling carcinogens out of the body or by halting malignant changes in cells that have been exposed to cancer-causing agents. Other foods with monoterpenes include celery and caraway and fennel seeds.

STRAWBERRIES. Strawberries, raspberries and grapes contain ellagic acid, which seems to prevent carcinogens from reaching or penetrating cells--at least in laboratory rodents. Ellagic acid holds up well under cooking, freezing and preservation. As a result, jams, frozen berries and juices are good off-season bets.

LICORICE ROOT. The glycyrrhizin in licorice root may protect against prostate cancer by preventing the conversion of testosterone to cancer- promoting dihydrotestosterone. But too much (what you would get in a steady diet of 10 licorice whips a day, say) can lead to very high blood pressure. Most American "licorice" candy is flavored with anise, which lacks glycyrrhizin.

SPINACH. Spinach and other dark-green, leafy vegetables are loaded with lutein and zeaxanthin, which cut the risk of blindness due to age-related macular degeneration--possibly by protecting the blood vessels that supply the retinas. Researchers recommend at least one weekly serving.

HOT PEPPERS. Old wisdom said to avoid hot peppers if you had an ulcer, but new research says the capsaicin they contain may help kill bacteria that cause ulcers. And it's likely that capsaicin neutralizes the carcinogenic effect of nitrosamines, found in many meats like hot dogs and sausages.

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