DESCRIPTION (provided by applicant): Vasomotor symptoms (VMS), including hot flashes and night sweats, affect the majority of menopausal women. Since the results of the Women's Health Initiative were publicized, many women and their health care providers no longer wish to use hormone therapy for VMS. Soy isoflavones have been marketed for reducing VMS, but data are inconclusive as to their effectiveness. Although isoflavones are structurally similar to estrogen and thus bind to estrogen receptors, results from randomized controlled trials of both soy foods and supplements have been mixed. Given the pharmacokinetic characteristics of soy isoflavones, in particular the half-life (approximately 8 hours), dosing frequency may be critical to their effectiveness in reducing VMS. In addition, no intervention study of VMS has examined whether participants are equol producers. Equol, daidzein's active metabolite, may affect the efficacy of daidzein in reducing VMS intensity. We propose to conduct a small pilot randomized placebo-controlled trial under the R21 mechanism of 180 menopausal women with moderate to severe VMS to examine a range of doses (total daily dose of 100 mg/day and 200 mg/day) and three dosing frequencies (1, 2, and 3 times a day) of capsules containing the primary isoflavones found in soy (daidzein and genistein). Outcomes will include feasibility and preliminary dose evaluation. For feasibility aims we will: 1) assess our ability to recruit and retain participants; 2) measure adherence to capsules and to completing symptoms diaries; 3) modify and test a daily symptoms diary that is more complex than previously used; and 4) test the feasibility and utility of identifying equol producer status. For preliminary dose evaluation aims we will examine VMS as they relate to: 1) isoflavones by dose amount and dose frequency; 2) equol producer status; and 3) in a subgroup, steady state concentrations. These data will provide essential information for optimal study design, methods of data collection, and total daily dose and dosing frequency for a larger, more definitive randomized controlled trial.