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Diet, Metformin and PCOS

The recommendations based on international evidence -based guideline for the assessment and management of polycystic ovary syndrome 2018 (1)

PCOS creates an insulin resistant state and can have significant metabolic effects. There is a huge amount of information of decreasing weight and its impact of reducing the symptoms and the biochemical aspects of PCOS. What is less know is whether dietary interventions are effective for improving weight loss, metabolic, fertility and emotional wellbeing.  Whether specific dietary composition in lifestyle intervention is successful is controversial though it is marketed extensively.

Having reviewed the recent evidence which reviewed outcomes from a high protein diet to a high carbohydrate diet no evidence was found for the majority of anthropometric, metabolic, fertility and emotional well being; ie. the type of diet was not found to be effective in these studies.  However it was found that regardless of the type of diet, diet aimed at reducing weight was of benefit to women with PCOS.  Two large systematic reviews showed that there was no benefit with a specific diet and hormone level changes as well as insulin changes did not predict response . It was noted that weight loss was possible and patient complaint with low fat diet and reduced energy diets, though adding different micronutrient content seemed unjustified  (2,3).

Is metformin alone, or in combination, effective for management of PCOS?

Metformin is a low cost, readily available medication that has been extensively used as an insulin sensitiser for over seven decades in DM2 and for several decades in PCOS. Insulin resistance is documented on clamp studies in 75% of lean women and 95% of overweight women and addressing this has underpinned the use of metformin in PCOS. Metformin is currently widely used by women with PCOS, yet the efficacy of metformin in terms of improving clinical outcomes remains uncertain. Side effects do cause concern, and metformin use in PCOS is generally off label.

In PCOS, evidence indicates that metformin is effective overall in improving weight but I suspect that this is mainly due to the side effects of metformin; nausea, vomiting and diarrhoea!


  1. International evidence-based guideline for the assessment and management of polycystic ovary syndrome 2018 :http://www.monash.edu/medicine/sphpm/mchri/pcos
  2. Johnston, B.C., et al., Comparison of weight loss among named diet programs in overweight and obese adults:a meta-analysis. JAMA, 2014. 312(9): p. 923-33.
  3. Gardner, C.D., et al., Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: The dietfits randomized clinical trial. JAMA, 2018.319(7): p. 667-679.



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