Limited data are available evaluating the effects of soy isoflavones on metabolic status of patients with polycystic ovary syndrome (PCOS).

The current study was performed to determine the effects of soy isoflavones on metabolic status of patients with PCOS.

This randomized, double-blind, placebo-controlled trial was performed on 70 women diagnosed with PCOS according to the Rotterdam criteria who were 18–40 years old. Participants were randomly allocated into two groups to take either 50 mg/d soy isoflavones (n = 35) or placebo (n = 35) for 12 weeks. Metabolic, endocrine, inflammation, and oxidative stress biomarkers were quantified at the beginning of the study and after the 12-week intervention.

After 12 weeks of intervention, compared to the placebo group, soy isoflavone administration significantly decreased circulating serum levels of insulin (−1.2 ± 4.0 vs +2.8 ± 4.7 μ IU/mL; P < .001) and homeostasis model of assessment-estimated insulin resistance (−0.3 ± 1.0 vs +0.6 ± 1.1; P < .001) and increased the quantitative insulin sensitivity check index (+0.0009 ± 0.01 vs −0.01 ± 0.03; P = .01). Supplementation with soy isoflavones resulted in significant reductions in free androgen index (−0.03 ± 0.04 vs +0.02 ± 0.03; P < .001) and serum triglycerides (−13.3 ± 62.2 vs +10.3 ± 24.5 mg/dL; P = .04) compared to the placebo group. There was a significant increase in plasma total glutathione (+96.0 ± 102.2 vs +22.7 ± 157.8 μ mol/L; P = .04) and a significant decrease in malondialdehyde levels (−0.7 ± 0.8 vs +0.8 ± 2.3 μ mol/L; P = .001) by soy isoflavone intake compared with the placebo group. We did not observe any significant effect of soy isoflavone intake on other lipid profiles and inflammatory and oxidative stress markers.

Soy isoflavone administration for 12 weeks in women with PCOS significantly improved markers of insulin resistance, hormonal status, triglycerides, and biomarkers of oxidative stress.