It's alluring to think that, one day, a chemical distilled from a source as mundane as sweet potatoes or brussels sprouts could provide the genesis of a cure for cancer. So appealing, in fact, that researchers around the world are studying hundreds of vitamins, minerals, and chemicals found in the plants we dine on. And evidence is mounting that certain foods can play an important role in fighting cancers.
PRESCRIPTIONS. But science has a long way to go before it can definitively proclaim that eating more carrots will protect against lung disease or soybean burgers will ward off breast cancer. "Science is approaching this in a very systematic way," says Carolyn Clifford, chief of the diet and cancer branch of the National Cancer Institute. "In the meantime, the public is looking for a silver bullet."
For now, the medical community's strongest prescription is simply to cut down on saturated fat and eat more fruits, vegetables, and grains. Still, discoveries in the laboratory are moving ever closer to practical application for cancer prevention and treatment--and the public is hungry for more advice.
Take garlic. It's already well documented that eating a clove or two a day can reduce blood pressure, as well as cholesterol levels. But researchers are now zeroing in on chemicals in garlic that may aid in the battle against colon and breast cancers.
A recent study at Pennsylvania State University showed that a compound in garlic, diallyl disulfide, shuts down or kills human colon cancer cells transplanted into mice. "We are still in the beginning stages of exploring," says Sujatha Sundaram, a PhD student who co-led the study. In the meantime, "incorporating more garlic into the diet could probably help," she says. Hopes for garlic are running so high that Cornell Medical Center has established the Garlic Information Hotline (800 330-5922) to field the public's questions about the uses of the pungent herb.
KEEPING THE DR. AWAY. Diallyl disulfide is just one of hundreds of little-known compounds, called phytochemicals, found in fruits, vegetables, and grains. Many have no known nutritional value but some may have medicinal properties, including the ability to inhibit tumor growth, says Barbara Levine, research coordinator of the Clinical Nutrition Research Unit at New York Hospital-Cornell Medical Center.
Phytochemicals appear in the likes of green tea; cruciferous vegetables, such as broccoli, kale, and cabbage; citrus fruits; and the allium genus of vegetables, which includes garlic and onions. Isothiocyanates from cruciferous vegetables appear to block carcinogens from damaging a cell's DNA. Isoflavones, found in soybeans, may reduce estrogen-related cancers in women. And coumarins, contained in citrus fruits such as lemons and oranges, produce enzymes which seem to slow down tumor growth.
Important research is also documenting the cancer-fighting properties of antioxidant vitamins, such as E and C, selenium, and beta-carotene, (which turns into vitamin A). They are believed to reduce damage caused by rogue atoms of oxygen in the bloodstream called free radicals. For example, beta-carotene, found in orange and red vegetables such as carrots and peppers, protects the cell membranes in the mouth, nose, throat, and lungs, potentially helping to ward off lung cancer.
But medical research can be tricky, and hopes that beta-carotene would prove to be the next wonder drug were tempered in April, 1994, when supplements were linked to an increase in deaths from lung cancer and heart disease in Finnish men who were lifelong smokers. Some scientists think the high dose of beta-carotene may have blocked the positive effects of other chemicals in the diet.
For now, there is no point in running out to the health-food store in search of broccoli pills. "Rather than buy some phytochemical supplement that's marketed as if it has some benefit, we'd rather people just ate the fruits and vegetables," says Bonnie Liebman, director of nutrition at the Washington-based Center for Science in the Public Interest. That way, if studies ever prove that carrots can cure cancer, you will be way ahead of the game.
Researchers are investigating whether chemical compounds found in plants, called phytochemicals, can help prevent and treat cancers.
FOOD PHYTOCHEMICALS POSSIBLE BENEFITS
BROCCOLI, Isothiocyanates, Could reduce risk of breast
CABBAGE, thiocyanates, cancer or stop carcinogens
CAULIFLOWER indoles from damaging a cell's DNA
CITRUS FRUIT Coumarins, May inhibit tumor growth,
limonene help cells dispose of
GARLIC, Allium May make it easier for body to
ONIONS, compounds excrete carcinogens or block
SCALLIONS reproduction of tumor cells
SOYBEANS, Isoflavones, May help prevent colon cancer
DRIED BEANS phytosterols and reduce risk of breast or
YELLOW AND Carotenoids, Contains antioxidants, which
ORANGE such as may block damage to cell
VEGETABLES beta-carotene DNA
DATA: CENTER FOR SCIENCE IN THE PUBLIC INTEREST; BARBARA LEVINE, PhD