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B.A., Harford, Connecticut, October 2015
A: Whole soy foods like tofu, tempeh, edamame, soy milk, and soy nuts contain many important nutrients and phytonutrients that have been shown to be beneficial to our overall health. These whole soy foods are a good source of protein, fiber, potassium, magnesium, copper and healthy fat as well.
The concern with soy and cancer comes from the fact that soy contains isoflavones, which are phytoestrogens that in some ways mimic the action of estrogen. However, these phytoestrogens are many times weaker than the estrogen made in human bodies. According to the American Institute for Cancer Research and American Cancer Society, research has shown that moderate consumption of whole soy foods appears safe for both breast cancer survivors and the general public. Moderate consumption of whole soy foods, or 1-2 servings per day, does not increase cancer risk, and may actually lower the risk of cancers of the breast, prostate, and other cancers. One serving is one cup of soy milk, a half cup of cooked edamame or soy beans, or one ounce of soy nuts.
That being said, research is lacking in regard to high doses of soy in supplements like soy protein isolates. Since less is known about their effects on health, isolated soy compounds or soy supplements should be avoided if that is a concern. Avoid foods made from soy protein powder, soy protein isolate (as you mentioned), or isolated soy protein (read the ingredient list to look for these). These forms of soy are often found in nutrition bars, soy protein powder, many high protein breads and cereals and vegetarian "meat-less" options, such as certain brands of veggie burgers or soy hot dogs.
Soy lecithin, extracted from soy-bean oil, is often used in numerous foods, like chocolate to help keep ingredients emulsified. Many food labels will list a soy-based emulsifier like lecithin. The amounts are generally minute and don't contribute a substantial level of phytoestrogens. Products with soy lecithin do not need to be avoided because they have such minor amounts.