This will be a double blind, Phase I, multiple dose clinical trial of orally administered soy isoflavones (PTI G-2535, 70% unconjugated isoflavones containing genistein, daidzein, and glycitein). This preparation will be referred to as soy isoflavones in this and all study related documents to more accurately reflect the study drug’s content. The multiple dose trial will last four months (112 days) and will include healthy, post-menopausal women as determined by FSH levels and lack of spontaneous bleeding for at least one year. After eligibility is determined, all potential subjects will ingest a soy shake to determine if they are producers of the daidzein metabolite, equol. We expect to find approximately 30% of our eligible subjects to be equol-producers as published in the literature. Equol producers will be defined as individuals with plasma levels >20ug/L; non-equol producers as those with <10ug/L 37. Individuals with intermediate equol values (> 10 ug/L to < 20 ug/L) will be excluded from the study. Stratified randomization will assign the subjects to one of the two groups, aiming for 30-40% equol producers in each group. Group 1 (20 subjects) will receive a dietary supplement containing 600 mg of genistein in two doses of 300 mg (as part of a soy isoflavones mixture) per day orally administered over an 84-day period. Group 2 (10 subjects) will receive a placebo supplement (excipients from the active formulation), orally administered over an 84-day period. These women will be recruited from the local population within the Research Triangle area. The study will be conducted at the UNC Hospital General Clinical Research Center (GCRC).