A mild favorable effect of soy protein with isoflavones on body composition--a 6-month double-blind randomized placebo-controlled trial among Chinese postmenopausal women.

BACKGROUND: In vitro and animal studies suggested that soy protein and isoflavones promote weight and body fat loss. However, clinical trials in humans were few and the effects remained uncertain.

OBJECTIVES: To examine whether soy protein with isoflavones and isoflavone extracts exert beneficial effects on body composition among postmenopausal women.

DESIGN: A double-blind randomized placebo-controlled trial was conducted among 180 postmenopausal Chinese women with mild hyperglycemia. After a 2-week adaptation, participants were randomly assigned to one of the three arms to receive 15 g soy protein and 100 mg isoflavones (Soy group), or 15 g milk protein and 100 mg isoflavones (Iso group), or 15 g milk protein (placebo group) on a daily basis for 6 months.

RESULTS: We observed a mild but significant favorable effect of soy protein with isoflavones on the changes of body weight (BW), body mass index, and body fat percentage relative to isoflavone extracts and milk protein after 6-month supplementation. The mean differences of BW between the Soy and the Iso groups were -0.75 kg (95% CI: -1.363 to -0.136, P=0.017), and between the Soy and the placebo groups were -0.60 kg (95% CI: -1.209 to -0.019, P=0.047). The mean difference of change percentage in body fat percentage between the Soy and the Iso groups was -3.74% (95% CI: -6.88 to -0.60%, P=0.02), and between the Soy and the placebo groups was -2.54% (95% CI: -5.69 to 0.12%. P=0.08).

CONCLUSIONS: Six-month supplementation of soy protein with isoflavones had a mild favorable effect on body composition in postmenopausal women.