Soy Nutrition Institute
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Mar 30, 2012

Isoflavones, Weight loss and Glycemic Control

Zhang YB, Chen WH, Guo JJ, et al. Soy isoflavone supplementation could reduce body weight and improve glucose metabolism in non-Asian postmenopausal women-A meta-analysis. Nutrition 2012.

OBJECTIVE: The objective of this study was to conduct a systematic review and a meta-analysis to confirm the effects of soy isoflavone supplementation on body weight, fasting glucose, and insulin level in non-Asian postmenopausal women. METHODS: We searched the PubMed, EMBASE, and Cochrane databases up to October 2010 for randomized controlled trials regarding the effects of isoflavone supplementation on body weight, fasting glucose, and insulin level. Pooled estimates and 95% confidence intervals (CIs) were calculated by the fixed-and-random-effects model. RESULTS: Nine studies with 528 participants for body weight, 11 studies with 1182 participants for fasting glucose, and 11 studies with 1142 participants for fasting insulin were included, respectively. Significant reductions were found in body weight [weighted mean difference (WMD), -0.515; 95%CI: -0.895 to -0.134; P = 0.008), glucose level (WMD, -0.189; 95%CI: -0.344 to -0.033), and fasting insulin level (WMD, -0.940; 95%CI: -1.721 to -0.159) with soy isoflavone supplementation compared with placebo control group in non-Asian postmenopausal women after adjusted by unpublished studies. Furthermore, isoflavone supplementation in shorter duration (<6 mo) could significantly reduce body weight (WMD, -0.506; 95%CI: -0.888 to -0.124; P = 0.009) and longer duration (>/=6 mo) could significantly reduce blood glucose in postmenopausal women (WMD, -0.270; 95%CI: -0.430 to -0.110; P = 0.001). Meanwhile, more reduction in body weight was observed in the lower dose subgroup (dose < 100 mg). Moreover, it is more effective to reduce body weight and fasting insulin level with soy isoflavone supplementation in normal weight (body mass index < 30) than obese (body mass index >/= 30) women. CONCLUSIONS: This meta-analysis showed soy isoflavone supplementation could be beneficial for body weight reduction, glucose, and insulin control in plasma. Large and well-designed studies are recommended to confirm this conclusion.

Comment

The findings of this meta-analysis suggest that soyfoods may have a role in helping to control the diabesity epidemic. There are a number of strengths to this research; for example, the authors evaluated study quality and identified possible sources of bias.  However, in many of the studies included in this meta-analysis, body weight and glucose and insulin control were secondary endpoints.  When this is the case, it is not possible to draw definitive conclusions about the effects on these endpoints.  Also, this research did not separately analyze the effects from studies that intervened with isoflavone supplements and those that used isoflavone-rich soy protein.  Therefore, while the results of the meta-analysis are intriguing, larger and longer clinical trials specifically designed to evaluate the endpoints in question are needed before reaching conclusions.