Effects of high-dose isoflavones on metabolic and inflammatory markers in healthy postmenopausal women.

OBJECTIVE: After menopause, women experience changes in body composition, especially an increase in fat mass. In addition, advancing age, decreased physical activity, and increased inflammation may predispose them to develop type 2 diabetes. Isoflavones have been shown to improve metabolic parameters in postmenopausal women. However, the effect of isoflavones on adipokines/cytokines remains unclear. The purpose of this study was to evaluate the effect of high-dose isoflavones on inflammatory and metabolic markers in postmenopausal women.

METHODS: We measured glucose, insulin, and adipokines/cytokines in 75 healthy postmenopausal women who were randomized to receive 20 g of soy protein with 160 mg of total isoflavones (64 mg genistein, 63 mg daidzein, and 34 mg glycitein) or 20 g of soy protein placebo for 12 weeks. Women taking estrogen discontinued therapy at least 3 months before the study. The supplements were given in a powder form and consumed once daily with milk or other beverages.

RESULTS: Mean ages in the placebo and active groups were similar (P = 0.4). Average time since menopause was 9 years, and two thirds of the women underwent natural menopause. There was no significant difference in body mass index at baseline between the groups (placebo, 25.1 kg/m; active, 26 kg/m) and it did not change significantly during the study. At baseline, the placebo group had significantly higher levels of tumor necrosis factor alpha (P < 0.0001); otherwise, there was no difference in any other parameter. After 12 weeks of treatment, there were significant positive changes in tumor necrosis factor alpha levels within the placebo group (P < 0.0001) and adiponectin levels within the isoflavone group (P = 0.03). Comparison of pre-post change between the groups showed a small but significant increase in serum adiponectin levels in the isoflavone group (P = 0.03) compared with the placebo group. No significant changes were seen in any other parameter between the two groups.

CONCLUSIONS: Healthy, normal-weight postmenopausal women may not experience improvement in metabolic parameters when given high-dose isoflavones despite an increase in serum adiponectin levels. The role of isoflavones in obese and insulin-resistant postmenopausal women needs exploration.