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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 women’s 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 day—also
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.
Additional Resources and References
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