Does soy affect breast cancer risk?
Studies show that eating a moderate amount of soy foods does not increase risk of breast cancer — or other types of cancer. A moderate amount is considered one to two servings a day of whole-soy foods, such as tofu, soy milk and edamame. Soy contains protein, isoflavones and fiber, all thought to provide health benefits.
So where did the idea come from that soy increases breast cancer risk? Isoflavones, which are found in soy, are plant estrogens. High levels of estrogen have been linked to an increased risk of breast cancer. However, food sources of soy don't contain high enough levels of isoflavones to increase the risk of breast cancer.