The effect of dietary soy supplementation on hot flushes.

OBJECTIVE: To assess the effect of daily dietary supplementation of soy protein isolate powder on hot flushes in postmenopausal women. METHODS: We carried out a double-blind, parallel, multicenter, randomized placebo-controlled trial of 104 postmenopausal women. Fifty-one patients (age range 48-61 years) took 60 g of products containing 40 g of isolated soy protein [corrected] daily and 53 patients (age range 45-62 years) took 60 g of placebo (casein) daily. The study lasted 12 weeks. Using analysis of covariance, we analyzed changes from baseline in mean number of moderate to severe hot flushes (including night sweats) during treatment. RESULTS: Soy was significantly superior to placebo (P < .01 in reducing the mean number of hot flushes per 24 hours after 4, 8, and 12 weeks of treatment. In particular, women taking soy had a 26% reduction in the mean number of hot flushes by week 3 and a 33% reduction by week 4 (P < .001 by the Wilcoxon exact test). By the end of the 12th week, patients taking soy had a 45% reduction in their daily hot flushes versus a 30% reduction obtained with the placebo (P < .01). The overall rates of adverse effects were similar for soy and casein-placebo. Twenty-five patients dropped out of the study: 11 in the soy group and 14 in the placebo group. Gastrointestinal side effects were the most common cause of premature withdrawal from the study (seven patients in each group). CONCLUSION: Soy protein isolate added daily to the diet substantially reduced the frequency of hot flushes in climacteric women.