Studies have found that soy protein may reduce the risk for certain cancers, including breast, colon, and prostate cancer.
According to a study in the Journal of the American Medical Association, 5,042 women who were previously diagnosed with breast cancer participated in the Shanghai Breast Cancer Survival Study over a four-year period. The study reported that women who regularly consumed soy products, such as soymilk, tofu, or edamame, had a 32 percent lower risk of recurrence and a 29 percent decreased risk of death, compared with women who consumed little or no soy.
And it's not just breast cancer. According to a review of 14 studies published in the American Journal of Clinical Nutrition, increased intake of soy resulted in a 26 percent reduction in prostate cancer risk for men. (Note: no decrease in testosterone was found in men who consumed soy; that myth can be laid to rest.)
Why should soy products reduce cancer risk? Most research has focused on phytoestrogens found in soybeans (phyto means "plant”). Some researchers have suggested that these compounds somehow block the effects of estrogens.