Soy isoflavones and glucose metabolism in menopausal women: A systematic review and meta‐analysis of randomized controlled trials

Scope The aim of this meta‐analysis was to investigate whether soy isoflavones, a type of phytoestrogen, would affect glucose homeostasis in menopausal women. Methods and results Studies concerning about the relationship between soy isoflavone treatment and glucose metabolism were searched on MEDLINE and WEB OF SCIENCE (updated through April 2015) and EMBASE (1990–April 2015). Seventeen randomized controlled trials (RCTs) with a total number of 1529 menopausal women were identified for meta‐analysis. Soy isoflavones were found to show great significance for the improvement of glucose metabolism, though marked heterogeneity was found between studies. The overall results showed that the average difference in fasting blood glucose values between women assigned to soy isoflavones and women in placebo groups was −0.22 mmol/L (95% CI: −0.38 to −0.07 mmol/L) under a random‐effects model. In addition, the effect of soy isoflavones on insulin was also significant: −0.43 μIU/mL (95% CI: −0.71 to −0.14 μIU/mL), as was the effect on homeostasis model assessment insulin resistance (HOMA‐IR): −0.52 (95% CI: −0.76 to −0.28). Conclusion Although the results displayed a significant tendency in favor of soy isoflavones, it appears that genistein alone played an important role in improving glucose metabolism due to its low heterogeneity.