In PCOS, the strongest nutrition evidence points to supplements, not diets

Polycystic ovary syndrome, or PCOS, is a common hormonal condition in women that often brings insulin resistance, raised testosterone and difficulty ovulating. Nutrition is usually the first thing women with PCOS are told to change, and a large number of meta-analyses have tested diets and supplements against its metabolic and hormonal features. What nobody had clearly established was how strong that evidence actually is, or which interventions deserve the most confidence. This umbrella review set out to grade the whole field in one place.

The reviewers searched PubMed, Scopus and Web of Science from inception to March 2021 for meta-analyses of randomised controlled trials testing dietary modifications or supplements in women with PCOS. Twenty-eight meta-analyses qualified, together reporting 40 different outcomes. Two investigators independently extracted the data, assessed the quality of each meta-analysis and rated the certainty of every finding, with a third investigator confirming their work.

No diet alone showed high-certainty benefits: lower carbohydrate, DASH and lower glycaemic index or load diets improved some body and metabolic measures, but only with very low to low certainty. Supplements fared better. Probiotics and synbiotics reduced fasting glucose, fasting insulin and insulin resistance with moderate to high certainty, while curcumin, fish oil, omega-3, vitamin D and inositol each improved blood sugar or blood fat markers with moderate certainty. Fish oil raised adiponectin with high certainty, probiotics and synbiotics lowered total testosterone with moderate certainty, and in subfertile women inositol increased ovulation rates with moderate certainty.

This flips the usual emphasis: dietary advice dominates PCOS conversations, yet the graded evidence currently favours specific supplements for metabolic and hormonal outcomes. That does not mean diet is useless, only that the trials behind diet-only approaches are weaker and less certain. The review also leaves open whether these improvements in markers translate into longer-term outcomes such as fertility beyond ovulation, or reduced diabetes risk. Better designed diet trials could still change the balance.

For women managing PCOS, this is a reason to know that the evidence behind different nutrition strategies is not equal. Supplements such as probiotics, inositol, fish oil, vitamin D and curcumin currently carry more certain trial support for blood sugar and hormone markers than any diet pattern tested. It is information for a conversation with a clinician rather than a plan to follow. Individual needs vary, and certainty about blood markers is not the same as certainty about symptoms or fertility.