Regularly we are asked by our patients if eating soy increases their risk of developing breast cancer. Isoflavones, found in soy, are plant estrogens. And high levels of estrogen have been linked to an increased risk of breast cancer.
However, it is important to note, whole food sources of soy don’t contain high enough levels of isoflavones to increase the risk of breast cancer. Therefore eating a moderate amount of soy foods won’t increase risk of cancer.
We advise avoiding concentrated soy supplements entirely, but do recommend one to two servings a day of organic whole soy foods. A serving is a cup of soymilk or one half-cup of tofu, tempeh, edamame or soy nuts. At those amounts you’ll get the benefits of soy without the theoretical risks of taking in too many of the plant estrogens.
In fact, many studies show diets rich in whole soy foods actually reduces the risk of breast cancer in women! Soy contains protein, isoflavones and fiber, all of which provide many protective health benefits.
by 
