THE QUESTION Soy-based foods contain isoflavones, which act in a manner similar to estrogen, a natural hormone that is thought to play a role in the growth of cancer cells. Should women with breast cancer, then, avoid foods containing soy?
THIS STUDY analyzed data on 5,033 women who had surgery for breast cancer. In the next four years, 534 of them either had a cancer recurrence or died of the disease. Women who consumed, on average, the most soy (more than 15 grams of soy protein a day) were 32 percent less likely to have had their cancer return and 29 percent less likely to have died of breast cancer than were women who took in the least soy (less than five grams a day). The benefits were the same whether the women had breast cancer that was estrogen-receptor-positive or -negative. There was also no difference noted between women being treated with tamoxifen and those not being treated with the drug.