Soy isoflavones improve insulin sensitivity without changing serum leptin among postmenopausal women

To investigate the effect of a soy isoflavone extract over insulin sensitivity and plasma leptin levels.

Eighty postmenopausal women were randomly assigned to participate for 24 months either to a physical exercise and Mediterranean diet program (Control group: CG) or this intervention plus a daily oral intake of a soy isoflavone extract (Soy isoflavone group: SIG). Anthropometry, body composition analysis, blood biochemistry, menopausal symptoms and health-related quality of life were assessed at baseline and every 6 months.

Sixty-five women completed the protocol with no differences found among groups at baseline in age and time since the menopause. At month 24, body mass index (BMI) was lower in the SIG as compared to the CG. Fat mass, glucose, insulin, HOMA-IR, tumor necrosis factor-α (TNF-α), Kupperman Index and Cervantes Scale values significantly decreased in the SIG as compared to baseline and to CG values. Kupperman scores and serum TNF-α levels significantly decreased in both studied groups. No changes in plasma leptin levels were observed after 24 months within and between groups. When analysis was stratified according to BMI values, changes in the aforementioned parameters displayed a similar trend; however, the impact over glucose, insulin and HOMA-IR values was more evident among obese women assigned to the SIG.

Diet, physical exercise and a daily oral intake of soy isoflavones exerted a beneficial effect on the homeostatic model in postmenopausal women which was not related to significant changes in plasma leptin levels, despite a decrease in TNF-α, fat mass and Kupperman values.