Written by Jessica Patella, ND, from The Journal Nutrition, 2012.
Can a soy supplement help reduce weight? Research in postmenopausal women suggests that it can. Weight gain and abdominal obesity are common after menopause because of hormonal changes that also affect blood sugar and insulin resistance, increasing cardiovascular risk. Hormone replacement therapy appears to help, but its controversial adverse effects have led many women to seek natural alternatives.
A review of 31 recent studies supports findings that soy supplements may help postmenopausal women with weight reduction, glucose metabolism and insulin resistance.
Body weight
Nine randomized controlled trials with 528 participants were reviewed. Soy doses ranged from 40 to 160 mg and study durations from eight weeks to one year.
Weight reduction differed significantly in postmenopausal women taking soy. Supplements appeared to significantly reduce weight over shorter periods (under six months), with lower doses (under 100 mg) more effective than higher doses (over 100 mg). They were also more effective in normal-weight and mildly overweight women (BMI below 30) than in heavier women (BMI at least 30).
Blood sugar
Seven clinical trials included 601 postmenopausal women taking soy and 581 taking placebo. Doses ranged from 40 to 160 mg, and durations from three months to two years.
No significant overall differences appeared between groups. However, women taking soy longer (over six months) showed lower blood sugar than those taking it for shorter periods. Lower doses (under 100 mg) also appeared more effective.
Insulin
Seven clinical trials included 581 postmenopausal women taking soy and 561 controls. Fasting insulin decreased significantly with soy. A closer analysis showed a significant difference in fasting insulin in normal-weight or mildly overweight women compared with women with more marked excess weight (BMI over 30).
In conclusion
Soy supplements below 100 mg for under six months appear effective for weight reduction in normal-weight or mildly overweight women.
For blood sugar, a dose below 100 mg per decilitre for more than six months showed greater efficacy. Soy also reduced fasting insulin more effectively in normal-weight or mildly obese women.