Polycystic ovary syndrome (PCOS) affects up to 10 percent of women of child-bearing age and is a major cause of infertility. Insulin resistance is part of the syndrome, which also includes ovarian cysts, excess male hormones, and a lack of ovulation.

Weight loss is known to help reduce PCOS symptoms, but the optimal type of diet for women with this condition has not been clear, according to researcher Jennie C. Brand-Miller, PhD, of the University of Sydney, Australia.

So Brand-Miller and her colleagues asked 96 overweight and obese women with PCOS to follow one of two diets without any particular type of calorie restriction. One diet consisted of low-glycemic foods, and the other was a conventional “healthy” diet with similar levels of vitamins and minerals. The women were asked to stay on these diets for either 12 months or until they lost 7 percent of their body weight.

About half of the women dropped out of the study, leaving 29 on the low-glycemic diet and 20 on the conventional healthy diet. Among women who remained in the study, those following the low-glycemic diet had greater improvements in their blood sugar levels (based on an oral glucose-tolerance test). Women who also took metformin had a greater benefit in blood sugar levels.

Seventy-six percent of the women had irregular menstrual cycles when they began the study. The regularity of menstrual cycles improved in 95 percent of women eating a low-glycemic diet, compared with 63 percent on the conventional diet.

In addition, fibrinogen levels decreased in women eating the low-glycemic diet, indicating an anti-coagulant effect of the diet. Fibrinogen levels increased in the other women.

Reference: Marsh KA, Steinbeck KS, Atkinson FS, et al. Effect of a low glycemic index compared with a conventional healthy diet on polycystic ovary syndrome. American Journal of Clinical Nutrition, 2010: doi 10.3945/ajcn.2010.29261.