A two-year study failed to find that isoflavones alleviate hot flashes. However, because of the limitations of the study design, the findings are of little relevance. The FDA recommends that hot flash studies show efficacy within 4 weeks, that specific data on the number of hot flashes and severity of hot flashes be recorded, and that participants have at least 50 hot flashes per week. In the current study, neither specific data on frequency nor severity were provided. Rather, the investigators used a general questionnaire about whether vasomotor symptoms were bothersome and the data were only reported at baseline and then after one year. Also, the participants were asked to recall their degree of bother over the past month. Additionally, few women were bothered by symptoms. The primary focus of the study was to evaluate the effects of isoflavones on bone health, not hot flashes. Finally, because the study intervened with soygerm even in the high isoflavone group, subjects only ingested about 15 mg of genistein per day. A meta-analysis published early in 2012 found 19 mg is needed for efficacy.
Amato et al. Menopause 2012