b4d1ced9_sity_of_Michigan_Health_System__Why
[Recommendation] Stay tuned about soy [Why] 
The commonly held belief that eating soy foods will protect against breast cancer is far from proven. Asian countries in which soy consumption is high generally have a low incidence of breast cancer. However, the dietary habits in these countries are so different from diets in high-risk countries that attributing protection from breast cancer specifically to soy foods on the basis of this evidence alone is premature.79 Similarly, within a society, women who frequently consume tofu have been reported to be at low risk of breast cancer.80 Consumption of tofu might only be a marker for other dietary or lifestyle factors that are responsible for protection against breast cancer. Genistein, one of the isoflavones found in many soy foods, inhibits proliferation of breast cancer cells in test tube studies. Most animal studies report that soybeans and soy isoflavones protect against mammary cancer.81 However, the protective effect in animals have occurred primarily when soy has been administered before puberty.82 If the same holds true in humans, consuming soy products in adulthood might provide little, if any, protection against breast cancer. The findings of several recent studies suggest that consuming soy might, under some circumstances, increase the risk of breast cancer.83 , 84 , 85 , 86 , 87 When ovaries were removed from animals—a situation related to the condition of women who have had a total hysterectomy—dietary genistein was reported to increase the proliferation of breast cancer cells.88 When pregnant rats were given genistein injections, their female offspring were reported to be at greater risk of breast cancer.89 Although premenopausal women have shown decreases in estrogen levels in response to soy consumption,90 , 91 proestrogenic effects have also been reported.92 When premenopausal women were given soy isoflavones, an increase in breast secretions resulted—an effect thought to elevate the risk of breast cancer.93 In yet another trial, healthy breast cells from women previously given soy supplements containing isoflavones showed an increase in proliferation rates—an effect that might also increase the risk of breast cancer.94 The commonly held belief that consuming soybeans or isoflavones such as genistein will protect against breast cancer is, therefore, far from proven.95 , 96 , 97 , 98 , 99 Possibly, consuming soybeans in childhood may ultimately be proven to have a protective effect.100 Doing the same in adulthood, however, may have very different effects.101 , 102 , 103 , 104 , 105 Some scientists, at least under some circumstances, remain hopeful about the potential for soy to protect against breast cancer. These scientists recommend consumption of foods made from soy (such as tofu), as opposed to taking isoflavone supplements. Several substances in soybeans other than isoflavones have shown anticancer activity in preliminary research.106
Breast Cancer Prevention (Holistic) | University of Michigan Health System