Soy foods (tofu, edamame/soy beans, soy milk and yogurt, etc.) have been studied both in their ability to help prevent, or the possibility that they might promote, cancer in some people. While some studies show soy offers a protective effect against breast cancer, a few studies show the estrogen-like effects in isoflavones may be harmful for women with breast cancer. We do know that the phytoestrogens in soy foods are “anti-estrogens.” In other words, they may block estrogen from reaching the receptors - therefore potentially protecting women from developing breast cancer. However, at this point, American Institute for Cancer Research stresses that data on soy and breast cancer are not conclusive, and future studies will determine the direction of dietary recommendations.
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