Study: Soy May Help Prevent Breast Cancer (dateline September 6, 2002)
Another small study shows that a diet rich in soy can help prevent breast cancer. The latest study, which involved researchers from the National University of Singapore, Cancer Research U.K. and the U.S. National Cancer Institute, found that women who consumed large amounts of soy had less suspicious breast density patterns on their mammograms that put them at a lower risk of developing breast cancer, compared to women who did not eat an abundance of soy. Though much research is still needed to better understand the effects of soy on breast cancer risk, this latest study provides more promising data that soy may help protect against the disease.
To conduct the study, Rupert W. Jakes of the Yu National Medical Research Council Clinical Trials and Epidemiology Research Unit in Singapore, along with British and American colleagues, combined data from two studies. The first study involved tracking the amount of soy ingested by a group of Chinese women in Singapore while the second study used mammography to study breast density patterns in women.
Of the 406 women between the ages of 45 and 74 who participated in both studies, Jakes and his colleagues found that those women who consumed large amounts of soy in their diets were 60% less likely to have specific patterns of breast density which have been linked with a higher risk of breast cancer. Breast density may make breast cancer more difficult to detect on a mammogram, which can lead to a later diagnosis of breast cancer.
According to the researchers, this is the first study to focus on mammographic data in conjunction with a soy diet. Currently, researchers are unsure how soy may work to protect against breast cancer risk. Jake and his colleagues suggest that soy may extend womens menstrual cycles. Fewer menstrual cycles over a lifetime have been associated with a reduced risk of breast cancer. Other research focuses more on the contents of soy. For instance, soy contains natural chemicals called phytoestrogens, which may work as anti-estrogens against breast cancer development, similar to the drug tamoxifen. The theory is that soy, like tamoxifen, blocks the hormone estrogen from binding to estrogen receptors in breast cancer cells. Since some breast cancer cells depend on estrogen for survival, a lack of estrogen starves these cells, causing them to die.
Much research on soy focuses on Asian women because the incidence of breast cancer is significantly lower in Asian countries where the consumption of soy is high, compared to Western countries, such as the United States, where soy intake is relatively low.
Soy is found in a variety of foods, including soybeans, soy burgers, soy hot dogs, soy chicken, roasted soy nuts, soy milk, soy bacon, tofu, tempeh, bean paste, and soy parmesan. Powder-based soy that may be added to fruit, water, and ice to make shakes are available in most health food stores. Unflavored soy powders may be added to a variety of liquids including lemonade, fruit smoothies, or soups. The average amount of soy recommended for women to help protect against breast cancer is 35 grams per dayalso the average amount Asian women consume per day. Sixty grams is the maximum amount of soy used in U.S. clinical trials involving breast cancer patients.
Research on the association between soy and breast cancer is relatively new and larger studies are needed to determine how, and the extent to which, soy may help protect against the disease. Other studies have shown that soy may provide additional health benefits. The U.S. Food and Drug Administration (FDA) recently granted approval to the use of soy food labels that contain a phrase equivalent to: "25 grams of soy protein daily can reduce the risk of coronary heart disease by lowering blood cholesterol levels." Studies also suggest that soy may help relieve menopausal symptoms, such as hot flashes, and protect against the bone-thinning disease osteoporosis. However, because some research shows that excessive soy intake may be harmful, women should talk with their physicians before using soy supplements or significantly increasing their soy intake to help protect against disease.