Objective: The aim of this study was to evaluate whether a standard dose of 40 mg of soy isoflavones prescribed in routine clinical practice for treatment of menopausal symptoms has some influence on glucose homeostasis in postmenopausal women with insulin resistance (IR).
Methods: A total of 116 postmenopausal women with IR were randomly assigned to a group of Mediterranean diet and physical exercise (control group) or a group of Mediterranean diet, physical exercise, and daily oral ingestion of 40 mg of soy isoflavones (soy isoflavones group). Anthropometric measures, Kupperman Index values, Cervantes Scale score, and blood samples for glucose, insulin, lipid profile, creatinine, uric acid, homocysteine, folic acid, vitamin B12, selenium, and estradiol were determined at baseline and at intervals of 6, 12, 18, and 24 months.
Results: Mean homeostasis model assessment of IR (HOMA-IR) values remained unchanged from the baseline in the control group but steadily decreased in the soy isoflavones group at 6 months (P = 0.042). There were no statistically significant differences between both groups in mean HOMA-IR scores at baseline, but statistically significantly lower values were found in the soy isoflavones group at 6 months (P = 0.009), 12 months (P = 0.011), 18 months (P = 0.018), and 24 months (P = 0.012). Changes in HOMA-IR values were also clearly related to body mass index (P < 0.001), abdominal circumference (P < 0.001), and treatment (P = 0.044) when a linear regression analysis was carried out.
Conclusions: Daily intake of 40 mg of soy isoflavones together with a Mediterranean diet and exercise reduced IR in postmenopausal women who had IR in the first place. It was significantly better than lifestyle changes alone. If corroborated, this may be a useful intervention for these women.