Soyfood forms of phytoestrogens have been consumed in moderate amounts for centuries in Asian cultures with no adverse effects. Soyfood sources are recommended as part of a therapeutic and prophylactic diet instead of isoflavone supplements because the foods contain all the potential anti-cancer agents ingested by these protected populations with lower rates of breast cancer. The risk of breast cancer increases with age, and studies indicate that there is a genetic risk factor as well. Other possible risk factors include weight gain, physical inactivity, high fat intake, alcohol consumption, pesticide or chemical exposure and induced abortion. Soyfoods may be a contributing factor to the lower incidence of breast cancer among Japanese and Chinese women.
American women have five times the rate of breast cancers.
Isoflavones are currently the most intensively researched soy phytochemical with respect to breast cancer, although there is a growing body of literature supporting protease inhibitors as anticarcinogens. The average intake of soy protein in the Southeast Asian diet ranges from 10 to 50g per day in contrast to 1 to 3g per day consumed by Americans. This translates to 20 to 80 mg of isoflavones consumed per day by Asian women compared to American women, whose intake is less than 5mg per day. In light of the above, it is not recommended that post-menopausal women with estrogen responsive tumors consume high doses of isolated isoflavones. There are a number of concerns regarding commercially prepared soy isolates as nutritional supplements.