Data from nine randomized clinical trials indicated that, for doses of soy isoflavones from 40 to 160 milligrams per day, supplementation was associated with significant reductions in body weight in both short and longer term studies.
Writing in Nutrition, scientists from Harbin Medical University in China report that isoflavone supplements were also associated with improvements in glucose metabolism, compared with control groups.
“Soy isoflavone supplementation could reduce body weight and improve glucose metabolism significantly with soy isoflavone supplementation compared with the placebo control group in non-Asian postmenopausal women,” they wrote.
“Furthermore, shorter supplement duration could significantly reduce body weight, whereas longer supplement duration could reduce blood glucose remarkably. Moreover, it is more effective to reduce body weight and fasting insulin level with soy isoflavone supplementation in normal weight than obese women.”
Isoflavones are well known phytoestrogens - active substances derived from plants that have a weak estrogen-like action.
Isoflavones from soy have been reported to provide a number of health benefits, including the promotion of heart health and the maintenance of bone health in post-menopausal women.
They have also been studied for their role in cancer prevention and slowing down the aging process in peri-menopausal women, and have proved to be a popular alternative to hormone replacement therapy for those wishing to control menopause symptoms without resorting to drugs.
In order to confirm the potential heart benefits of soy isoflavones, the researchers performed a systematic review and meta-analysis of the effects of isoflavone supplementation on various cardiovascular disease risk factors, including body weight, and glucose and insulin levels in non-Asian postmenopausal women.
The researchers pooled data from nine studies for body weight (528 participants), 11 studies for fasting glucose (1182 participants), and 11 studies for fasting insulin (1142 participants).
Results showed that soy isoflavone supplementation was associated with significant reductions in all three measures, compared with placebo groups in non-Asian postmenopausal women.
In addition, shorter term supplementation was effective to reduce body weight, and the lower doses were more effective for body weight reductions, they said.
“Our results are statistically robust and yield important conclusions,” they wrote. “A previous meta-analysis made by Reynolds et al. [Am J Cardiol, 2006, Vol. 98, pp. 633–640] has already found that isoflavone could improve blood fat levels. Hence, dietary isoflavone supplementation may have a potential beneficial effect with regard to atherogenesis and diabetes. However, large and well-designed studies along with high-quality scores are also recommended.”
Published online ahead of print, doi: 10.1016/j.nut.2012.03.019
“Soy isoflavone supplementation could reduce body weight and improve glucose metabolism in non-Asian postmenopausal women—A meta-analysis”
Authors: Y-B. Zhang, W-H. Chen, J-J. Guo, Z-H. Fu, C. Yi, M. Zhang, X-L. Na