A review of 34 randomised trials in PLoS Medicine has tested the standard first-line advice for polyendocrine metabolic ovarian syndrome (PMOS) — the condition long called polycystic ovary syndrome, or PCOS, recently renamed by an international consensus. Structured diet, exercise and behavioural programmes improved fasting insulin, and made regular menstrual cycles more likely, compared with minimal or no treatment. Their effect on body weight across all women was small, and the confidence interval included no effect at all. In women with overweight or obesity, weight did fall by about 2 kg.
What the review found
The team, from the Universities of Birmingham and Liverpool and Monash University, pooled 34 trials with 1,871 women. Programmes lasted at least two weeks and were compared with no treatment, usual care or brief unstructured advice. About a third of the trials (12 of 34) were rated at high risk of bias overall.
Across all trials, lifestyle programmes lowered fasting insulin by an average of 6.08 pmol/L (95% confidence interval 2.30 to 9.86 lower; 18 trials, 824 women), fasting glucose by 0.13 mmol/L (0.02 to 0.25 lower) and waist circumference by 2.38 cm (0.08 to 4.68 cm smaller). Women in the programmes had about four times the odds of regular cycles (odds ratio 4.03), but that figure rests on five trials and 237 women, and its interval runs from 1.16 to 14.05 — a range too wide to say whether the effect is modest or large.
Weight told a different story. The pooled difference was 1.97 kg (from 4.04 kg lower to 0.11 kg higher; 21 trials, 1,065 women), and body mass index did not change significantly. Only in the nine trials that enrolled women with overweight or obesity was the weight effect clear: 2.19 kg lower (1.02 to 3.35 kg), with little disagreement between trials. By type, exercise programmes did most for waist size and fasting insulin; diet programmes did most for fasting glucose.
When the 12 high-risk-of-bias trials were removed, only the fasting insulin result held (5.71 pmol/L lower, interval 1.83 to 9.60). The glucose and waist effects shrank and their intervals crossed zero.
How this fits
PMOS affects an estimated 10% to 13% of women of reproductive age and is tied closely to insulin resistance, which is why lifestyle change sits at the top of international guidance. This review broadly supports that position, but it reframes what the evidence shows. The consistent, robust benefit is metabolic — lower insulin — rather than a large change on the scale. That matters because weight loss is often presented as the goal. On these data, the insulin improvement in trials did not depend on much weight coming off, and in women without overweight the trials showed no weight effect at all.
The review did not compare lifestyle programmes with drugs. Women with PMOS and obesity are increasingly prescribed GLP-1 medications, and nothing here says how the two compare or combine; our research news covers those trials as they report.
What is not yet known
Heterogeneity was high for most outcomes — 90% for waist circumference and 86% for weight — meaning the trials disagreed with each other considerably, so the average hides a wide range of results. Many trials were small and short: interventions lasting over three months showed no clearer weight effect than shorter ones. Only one trial reported live births, and it found no significant difference (39.8% against 38.3%), so the review cannot say whether these programmes change fertility outcomes. The comparison group was minimal treatment, so the results show that a structured programme beats little or nothing, not which programme is best.
Sources: Olalere O, Koh MD, Crabb K, Ajijola O, Tariq S, et al. “The effect of lifestyle interventions in women with polyendocrine metabolic ovarian syndrome: A systematic review and meta-analysis.” PLoS Medicine 23(9): e1004887, published 23 September 2026. doi:10.1371/journal.pmed.1004887.
