You (and everyone, for that matter) should avoid soy extracts, that is, pills or powders that contain concentrated forms of soy, often referred to as soy isoflavones or soy protein isolates.
Anytime we try to extract and concentrate a substance from nature’s foods (such as beta carotene from carrots, or lycopene from tomatoes), the substance ends up having a completely different reaction in our bodies compared to the same substance in its original “package.” Sometimes, the reaction from these mega-doses in pills and powders may be the opposite of the reaction from food. These concentrated forms, in short, may be harmful rather than beneficial.
The good news
Soy foods appear harmless. Indeed, soybean foods like tofu, edamame, tempeh, and soymilk may actually decrease the risk of breast cancer’s return. In the landmark Shanghai Breast Cancer Survival Study published in JAMA (December 2009), researchers studied 5,042 female breast cancer survivors. They found that the more soy foods these women ate, the greater their chances of avoiding the recurrence of breast cancer. The less likely they were to die as well.
There are other major plusses to eating soy foods, particularly if you’re eating them instead of animal protein and fatty dairy products. Soy foods like tofu, soymilk, tempeh, and edamame can help lower your LDL “bad” cholesterol and total cholesterol – big benefits for heart health. Eating soy foods may also enhance weight loss, improve blood sugar control, and reduce insulin levels.
The preponderance of scientific literature indicates that the amount of soy foods recommended on the Pritikin Eating Plan (a maximum of 2 cups of soymilk a day and 1 to 2 servings of soy foods like tofu a day) should in no way increase your risk of breast cancer recurrence, and may in fact decrease risk.