Written by Jessica Patella, ND. In reviews, consumption of soy isoflavones in postmenopausal women improved blood sugar, insulin and body weight.
Could soy isoflavones supplementation help reduce body weight? Research points to yes, in postmenopausal women (1). After menopause, weight gain and central obesity tend to occur with hormonal changes, which also alter glucose levels and insulin resistance (1). With these changes, there is also an increased risk of cardiovascular disease, which hormone replacement therapy has been shown to help (1,2,3). The downside is the controversial effects of hormone replacement therapy, which has led many women in search of alternatives (1).
A recent meta-analysis of 31 different research studies, supported findings that soy isoflavone supplementation could help postmenopausal women with weight loss, glucose metabolism and insulin resistance (1).
Body Weight
A total of nine randomized controlled trials with 528 participants were examined. The dosage of soy isoflavone supplementation varied from 40mg to 160mg and the duration varied from 8 weeks to 1 year. A significant difference in the reduction of body weight was found (WMD*, -0.515; 95%CI: -0.895 to -0.134; P=0.008) in the postmenopausal women with soy isoflavone supplementation. Additionally, soy isoflavone supplementation was shown to reduce body weight significantly in a shorter duration (less than 6 months) instead of a longer duration (greater than 6 months), and at a lower dose (less than 100mg) instead of a higher dose (greater than 100mg). Soy isoflavone supplementation was also more effective in normal or overweight women (BMI less than 30) compared to obese women (BMI greater than or equal to 30) (1).
Blood Glucose
A total of eleven clinical trials with 601 postmenopausal women supplementing soy isoflavones and 581 postmenopausal women taking a placebo control were examined. The dose of soy supplementation ranged from 40 mg to 160 mg and the duration varied from 3 months to 2 years. Overall, no significant results were detected (WMD, -0.143; 95%CI: -0.294 to 0.009; P=0.065). However, when comparing the longer duration (greater than 6 months) to the shorter duration (less than 6 months), participants supplementing soy over a longer duration had lower blood glucose. The lower dose (less than 100mg) also appeared to be more effective than the higher dose (greater than 100mg) (1).
Insulin
A total of eleven trials with 581 postmenopausal women supplementing soy isoflavones and 561 controls were examined. Overall, significant reductions in fasting insulin were found in the participants supplementing with soy isoflavones, compared to the controls (WMD, -0.940; 95%CI: -1.721 to -0.159; P=0.065). When examining the data further there was a significant difference in fasting insulin levels in the normal weight and over weight women (Body Mass Index (BMI) less than 30) compared to the obese women (BMI equal to or greater than 30) (1).
In conclusion, soy isoflavone supplementation seems most effective in reducing body weight in normal or overweight women with a lower dose of soy (less than 100 mg) in the shorter term (6 months or less). In regards to blood glucose levels, a lower dose (less than 100mg) over a longer duration (6 months or more) was most effective. Soy isoflavone supplementation was also found to reduce fasting insulin levels, these reductions were more prominent in normal weight and overweight women, compared to obese women. Larger studies are still recommended to further clarify results (1).
*Weighted Mean Difference (WMD): In a meta-analysis, when study results measured using the same scale are being combined, the difference between two means, weighted by the precision of the study.
Source: Zhang, Yun-Bo, et al. “Soy isoflavone supplementation could reduce body weight and improve glucose metabolism in non-Asian postmenopausal women—a meta-analysis.” Nutrition 29.1 (2013): 8-14.
© 2013 Elsevier Inc. All rights reserved.
Posted April 19, 2013.
Jessica Patella, ND, is a naturopathic physician specializing in nutrition and homeopathic medicine and offers a holistic approach to health. She earned her ND from Southwest College of Naturopathic Medicine in Tempe, AZ, and is a member of the North Carolina Association of Naturopathic Physicians. Visit her website at www.awarenesswellness.com.
References:
- Zhang Y-B, et al. Soy isoflavone supplementation could reduce body weight and improve glucose metabolism in non-Asian postmenopausal women. Nutrition (2012), doi:10.1016/j.nut2012.03.019.
- Tufano A, et al. Anthropometric, hormonal and biochemical differences in lean and obese women before and after menopause. J Endocrinol Invest 2004; 27 648-53.
- Sumino H, et al. Effects of hormone replacement therapy on weight, abdominal fat distribution, and lipid levels in Japanese postmenopausal women. Int J Obes Relat Metab Disord 2003; 27:1044-51.
