Effects of soy intake on sex hormone metabolism in premenopausal women

Studies suggest that phytoestrogens in soy products may impart hormonal eff ects that protect women against breast cancer. Limited research suggests th at intake of soy products high in isoflavonoid phytoestrogens affects sex h ormone metabolism, but it is unknown whether phytoestrogens in soy have any effect on menstrual function or serum sex hormones in women on common horm one therapies, such as oral contraceptives (OC). We studied the effects of soy in 36 premenopausal women, 20 of whom used OC. Subjects consumed their normal diet for two menstrual cycles and added a soy beverage containing 20 g of protein and 38 mg of total isoflavones to their usual diet for anothe r two menstrual cycles. No significant differences were observed in serum e strone, estradiol, sex hormone-binding globulin, dehydroepiandrosterone sul fate, prolactin, or progesterone concentrations with soy feeding in the non -OC or the OC group. No changes in menstrual cycle length or the urinary es trogen metabolite ratio of 2-hydroxyestrone to 16 alpha-hydroxyestrone were seen with soy feeding in the non-OC or the OC group. Levels of urinary est rogen metabolites were significantly different between the non-OC and the O C group. Thus soy consumption had no significant effect on the menstrual cy cle, serum sex hormones, or urinary estrogen metabolite ratio in premenopau sal OC or non-OC users.