Low-GI diets improve insulin, cholesterol and testosterone in PCOS

Polycystic ovary syndrome affects far more than the ovaries: women with PCOS commonly show insulin resistance, unfavourable blood lipids and raised androgens alongside menstrual and reproductive disruption. Lifestyle change, particularly diet, is recommended as the first-line therapy, yet beyond eating fewer calories the guidance has been vague about what kind of diet actually helps. The glycaemic index ranks carbohydrates by how sharply they raise blood glucose, and lower-GI eating is a plausible fit for a condition driven partly by insulin resistance. This review pooled the trial evidence to help update the international PCOS guideline.

The researchers systematically searched MEDLINE, Cochrane, Web of Science and Scopus through 30 October 2019, with a confirmation check on 25 March 2020, for randomised controlled trials of at least 8 weeks comparing lower glycaemic index or glycaemic load diets against higher ones in women with PCOS. Ten trials with 403 participants qualified: eight tested low-GI diets and two tested low-GL diets. The primary outcome was insulin resistance measured by HOMA-IR, alongside fasting insulin and glucose, blood lipids, body measurements and androgen status, pooled using random-effects models.

Lower-GI diets reduced HOMA-IR by 0.78 compared with higher-GI diets, and also lowered fasting insulin, total cholesterol, LDL cholesterol, triglycerides, waist circumference by 2.81 cm and total testosterone. Fasting glucose, HDL cholesterol, body weight and the free androgen index did not change significantly. The two low-GL trials produced some contradictory results and could not be pooled, so they were described only narratively. Notably, the improvement in the primary insulin measure came with substantial disagreement between the underlying studies, which tempers confidence in its exact size.

The findings support the idea that carbohydrate quality matters in PCOS beyond calorie counting, and the authors suggest they conceivably support including low-GI diets in the dietary management of the condition. This extends earlier lifestyle evidence that had focused mainly on energy restriction. What remains untested is whether these shifts in blood markers and waist size translate into the outcomes women with PCOS care most about, such as more regular ovulation, improved fertility and lower long-term cardiovascular risk. The authors explicitly call for further trials on those endpoints.

For anyone managing PCOS, this is a reason to think about which carbohydrates you eat, not only how much you eat overall. Lower-GI eating moved insulin resistance, cholesterol, waist size and testosterone in a favourable direction across pooled trials, even though body weight itself did not budge. It is equally worth knowing what this evidence does not yet show: an effect on cycles, fertility or heart disease has not been demonstrated, so the marker improvements are encouraging rather than conclusive.