Q. What’s the latest on soy and breast cancer; is it okay to eat soy or not?
A. Probably. The effect of soy on breast tumors has befuddled experts for years. As research continues, contradictory and controversial findings continue to come in.
Soy Rich in Phytonutrients. Interest in soy as a cancer preventive began because women in Asian countries, where soy consumption is high, have lower rates of breast cancer than in the U.S., where soy consumption is low. The theory that soy might somehow help prevent cancer also makes a certain amount of biological sense.
Soy is rich in isoflavones, phytonutrients structurally similar to the hormone estrogen. The cancer prevention theory contends that isoflavones in soy bind to estrogen-specific receptors on cells, thus blocking real estrogen from attaching and preventing estrogen-dependent tumors.
A Dark Side to Soy? But while Asian data link soy intake to lower breast cancer rates, some animal and laboratory studies suggest just the opposite’that the isoflavones in soy actually encourage cancer cells to develop and existing tumors to grow. Moreover, recent animal research from the University of Illinois reveals that isoflavones may cancel the therapeutic effects of the cancer treatment tamoxifen.
Timing Is Everything. Some researchers believe isoflavones affect breast cancer risk depending, in part, on when in life they are consumed. A large soy intake during adolescence, when breast development occurs, may be protective. But soy later in life might stimulate tumor growth.
Food vs Supplements. The bigger question of safety may be whether you?re talking about foods or supplements. Much of the research that found isoflavones to be risky looked only at isolated isoflavones, not soy foods. That’s of concern, because those most at risk for breast cancer are postmenopausal women, the same group to which isoflavone supplements are marketed.
Whole soy foods are complex mixtures of several active components, not just isoflavones. So consuming whole soy foods, like edamame, soy nuts, tofu or soy milk, is very different from taking isoflavone supplements. Recent findings from a Japanese study of more than 30,000 women who were followed for more than seven years bolster that notion and ease safety concerns about soy foods. It found no link?positive or negative? between soy foods and breast cancer.
EN‘s Bottom Line. It’s increasingly clear that taking isoflavone supplements may not be a smart move. While the risk is not proved, EN advises against their use. Three to four servings a week of whole soy foods, on the other hand, are still healthful high-protein additions to your diet, even if they don’t prevent cancer.