Updated: Dec 7, 2020
Polycystic ovarian syndrome (PCOS) is a complex endocrine condition which can causes distressing symptoms including irregular periods or no periods at all; difficulty getting pregnant; excessive hair growth; acne and thinning hair.
Many of the symptoms of PCOS are caused by excessive androgens - the male sex hormones. Both the adrenal glands and the ovaries can secrete too much of these male sex hormones, but why they do this is not fully understood. There may be some internal factors within the ovary which cause it to secrete more androgens, but there are external factors too. Of critical relevance to nutrition and lifestyle is the role of insulin.
Insulin resistance is more common in women with PCOS than women without PCOS. In most of the population, insulin resistance is linked with overweight and obesity. However, insulin resistance is also observed in lean women and adolescent girls of a “healthy” weight (body mass index of 18.5 to 25kg/m2) with PCOS, suggesting that it is an inherent clinical defect unrelated to weight gain. Insulin resistance is a problem because it can lead to the pancreas producing even more insulin to compensate for the insulin resistance. Too much insulin is called hyperinsulinaemia (literally: too much insulin in the blood). Too much insulin does two particular things which are especially detrimental to PCOS - first it makes the adrenal cortex and ovaries produce more androgens like testosterone- and it also reduces the amount of a steroid binding hormone produced by the liver. Steroid binding hormone globulin (SHBG) usually binds testosterone and reduces its activity in the body. In PCOS, low SBHG is associated with many of the health problems observed in PCOS such as type 2 diabetes, glucose intolerance, obesity, infertility, and cardiovascular disease.
Since insulin plays such a large part in causing the hormone disruption in PCOS, lifestyle management aims to reduce insulin. Critically, insulin is produced in the fasting state (ie when you have not eaten) and also following food or drink intake. For the management of PCOS it’s not known whether the fasting insulin or the after meal insulin is most important. So the safest bet is to address both.
The after-meal insulin is the easiest to change with diet. Low-carbohydrate diets can lower the insulin concentration after a meal though it’s not known how low a person needs to go because there aren’t many studies which measure the insulin after a meal. Nevertheless, a good place to start could be reducing the amount of starchy-carb by about half - and replacing the rest with non-starch vegetables like courgettes, peppers, spinach and broccoli. Replacing refined carbohydrate with higher-fibre less processed alternatives including quinoa, brown rice, kidney beans and lentils can also lower insulin after a meal.
On the other hand, fasting insulin is less related to food intake and may be more difficult to change, even with low-carbohydrate diets. There is some evidence that high fibre diets can lower fasting insulin when compared with refined starch diets.
Switching a meal pattern towards a “big breakfast/small dinner” approach lowers insulin, and improves androgens and SHBG in women with PCOS compared to “small breakfast/big dinner” and this type of dietary pattern is safe to follow and unlikely to have any detrimental effects.
Weight loss is also an important approach for management of PCOS in women who are overweight or obese as weight loss lowers both fasting and after meal insulin. In clinical practice, personalising the diet based on a patient’s preferences is key to ensuring a good quality of life, enjoyment of food and sustainability. Based on the data we have available on reducing carbohydrate and increasing fibre - integrating these approaches into a weight loss programme based on a patients’ tastes and food preferences should be first-line.
We often get a lot of questions about newer approaches to managing PCOS such as time restricted feeding. The truth is we do not have good data yet on whether these approaches could be effective for PCOS, but some studies are underway. Many investigators are urging caution about intermittent fasting and time-restricted feeding as many of the studies have important flaws; and the overall results are not always positive. Similarly, promise has been shown by a dietary supplement called inositol but as with all unregulated supplements it is difficult to know which type of supplement might be effective. Better standardisation and quality trials would help with understand how useful inositol could be in helping women with PCOS.