Fish oil did nothing for insulin resistance in PCOS

Polycystic ovary syndrome is closely tied to insulin resistance, which is why many women with the condition look to diet and supplements for help. Omega-3 fatty acids, the EPA and DHA found in fish oil, have been reported in several studies to improve insulin resistance in various diseases, so it is natural to assume the same benefit would carry over to PCOS. Fish oil is cheap, widely sold and heavily marketed for metabolic health, which raises the stakes for knowing whether it actually works in this group. Until this review, the effect of EPA and DHA supplementation on insulin resistance in PCOS remained unclear.

The authors searched MEDLINE, PubMed Central and EMBASE for English-language publications up to December 2015, looking for randomised controlled trials that tested omega-3 supplements against placebo for insulin resistance in women with PCOS. Out of 1202 papers screened, only three trials met the criteria, together covering 72 women given omega-3 and 73 given placebo. Doses ranged from 1.2 g to 3.6 g per day, and the trials ran for 6 to 8 weeks. Results were pooled as mean differences using a random-effects model, with standard checks for disagreement between the studies.

The primary result was a null. Omega-3 supplementation produced no significant improvement in insulin resistance compared with placebo, with a pooled mean difference of 6.18 that did not reach statistical significance. The same held for HOMA-IR, a standard calculated measure of insulin resistance, where the pooled difference was 0.276 and again not significant. Neither outcome moved in a way that could be distinguished from chance. The authors concluded that omega-3 supplementation may not have a beneficial effect on insulin resistance in women with PCOS.

This finding complicates a tidy story. Omega-3 fatty acids have shown promise for insulin resistance in other conditions, and the assumption that PCOS would respond the same way was plausible but untested. This pooled analysis suggests the benefit may not transfer, at least not at these doses and durations. The evidence base is very thin, though: three trials, around 145 women in total, and follow-up of two months at most. Whether higher doses, longer supplementation or larger samples would change the answer remains an open question.

For a reader with PCOS weighing up the supplement aisle, this is a reason not to expect fish oil to move the needle on insulin resistance specifically. The pooled trial evidence, limited as it is, points to no effect on the standard measures. That says nothing about other reasons people take omega-3, and it does not rule out a benefit that short, small trials simply could not detect. It does mean that any confident marketing claim linking fish oil to better insulin sensitivity in PCOS is running ahead of the evidence.