Can Food Fend Off Tumors?

Eating right to prevent heart disease may seem complicated and confusing, but it's a breeze compared with trying to design an anticancer diet. Cardiovascular disease is relatively simple; it's the result of normal bodily processes taken to the extreme. Cancer, by contrast, involves changes in the programming of DNA within the nuclei of individual cells. Beyond that, heart disease is an illness that affects a single organ system, while cancer is dozens of different diseases that target body parts as radically different as the brain, breast and bone.

That being the case, it's no surprise that the relationship between diet and cancer is still largely a matter of educated guesswork--and in many cases, the guesses have turned out to be wrong. Take the much publicized link between high-fat diets and breast cancer, for example. Women who live in Western countries, where high-fat diets are the norm, tend to have high breast-cancer rates. Even more telling: women of Japanese ancestry who live in the U.S. get the disease six times more often than their grandmothers and great-grandmothers in Japan. Yet a huge recent study of 90,000 women has refuted the breast cancer-fat link. Fat has also been suggested as a trigger for colon, prostate and bladder cancers--but there's no hard evidence that cutting fat will reduce your risk for any of these diseases.

A similar process of educated-guess-and-error led people to load up on the nutritional supplement beta carotene in the early 1990s. Scientists noted that those who eat lots of fruits and vegetables tend to get less cancer and speculated that carotenoids--the same antioxidant substances that seem to protect against heart disease--were responsible. In particular, they focused on beta carotene, the most abundant and common carotenoid, as the most likely to prevent cancer.

Yet a series of targeted studies in Finland and the U.S. showed that beta carotene supplements don't ward off cancer at all. This doesn't mean that a diet rich in fruits and vegetables doesn't reduce the risk of cancer, says Harvard's Walter Willett, or even that carotenoids aren't protective. But, he concludes, "it looks like taking beta carotene in high pharmacological doses is not the right thing to do."

The same sort of logic may apply to tomatoes and prostate cancer. Studies have shown that men who eat cooked tomatoes in various forms have a lower incidence of malignancy. The reason may be lycopene, another of the carotenoids, which is released when tomatoes are heated--but no one knows for sure, and even the tomato-prostate link isn't absolutely firm.

Another substance found in fruits and vegetables, though, does seem to have a protective effect against one form of malignancy: dietary fiber clearly reduces the risk of colon cancer. That link is sufficiently well established that the National Cancer Institute recommends that Americans increase their average daily fiber intake.