Two-week dietary soy supplementation has an estrogenic effect on normal premenopausal breast

An association has been reported between consumption of a high soy diet and a low incidence of breast cancer within populations of Southeast Asia. Phy toestrogens present in soy act as partial estrogen agonists or antagonists and can inhibit breast cancer cell proliferation in vitro. The effect of 14 -day dietary soy supplementation with 60 g (45 mg isoflavones) on the norma l breast of 84 premenopausal patients was determined. Serum concentrations of the isoflavanoids, genistein, daidzein, and equol, were raised in patien ts after soy supplementation (P less than or equal to 0.025). Nipple aspira te (NA) levels of genistein and daidzein were higher than paired serum leve ls, both before (P < 0.001 and P = 0.001, respectively) and after soy suppl ementation (P < 0.001 and P = 0.049, respectively); however, there was no s ignificant increase in NA isoflavone levels in response to soy. NA levels o f apolipoprotein D were significantly lowered and pS2 levels raised in resp onse to soy supplementation (P less than or equal to 0.002), indicative of an estrogenic stimulus. No effect of soy supplementation on breast epitheli al cell proliferation, estrogen and progesterone receptor status, apoptosis , mitosis, or Bcl-2 expression was detected. In conclusion, short term diet ary soy has a weak estrogenic response on the breast, as measured by nipple aspirate apolipoprotein D and pS2 expression. No antiestrogenic effect of soy on the breast was detected.