Natural estrogens from soy are associated with a decreased risk of breast cancer. However, don't load up on soy milk and cheese, which can cause a low thyroid. Use edamame (soy been pods) and tofu, in moderation, as they do in Asia.
This review and meta-analysis of 8 studies looked at the association between dietary soy intake and risk of breast cancer. Studies conducted among relatively high-soy-consuming Asian populations found that subjects consuming at least 20 mg per day isoflavones had a 29% reduced risk of breast cancer and those consuming approximately 10 mg/day had a 12% reduced risk relative to those consuming less than or equal to 5 mg/d isoflavones. Meanwhile, studies conducted among relatively low-soy-consuming Western populations did not find a protective effect of soy intake. The authors conclude, "Thus, the evidence to date, based largely on case-control studies, suggest that soy food intake in the amount consumed in Asian populations may have protective effects against breast cancer."
"Epidemiology of soy exposures and breast cancer risk," Wu AH, Yu MC, et al, Br J Cancer, 2008; 98(1): 9-14.
Jacob Teitelbaum, M.D. is one of the world's leading integrative medical authorities on fibromyalgia and chronic fatigue. He is the lead author of four research studies on their treatments, and has published numerous health & wellness books, including the bestseller on fibromyalgia and chronic fatigue syndrome From Fatigued to Fantastic! and his newer The Fatigue and Fibromyalgia Solution. Dr. Teitelbaum is one of the most frequently quoted fibromyalgia experts in the world and appears often as a guest on news and talk shows nationwide including Good Morning America, The Dr. Oz Show, Oprah & Friends, CNN, and Fox News Health.