Low-GI diet helps women with PCOS, but is there something that might work better?

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Polycystic ovarian syndrome (PCOS) is a condition characterised by multiples cysts in the ovaries, but also other symptoms such as hirsutism (abnormal hairiness) and acne that may result from higher than normal levels of androgens (‘male’ hormones) in the female body. I wrote about this condition back in 2003 (see here), where I made the point that the best diet, generally speaking, was one based on low glycaemic index (low GI) foods – i.e. foods that release sugar relatively slowly into the bloodstream.

One of the rationales here is that women with PCOS tend to be insulin resistant. In other words, their insulin tends not to work so well. The chief function of insulin is to reduce blood sugar levels. So, if insulin isn’t working too well, it makes sense to avoid eating foods that cause spikes in blood sugar. Also, there is an idea that higher levels of insulin (common in insulin resistance) can stimulate androgen release. At the time, the idea of eating a low-GI diet was based on common sense and first principles. Recently, though, a group of scientists decided to test the merits of low-GI eating in the real world [1].

96 women started the study, and were assigned to either a low-GI diet or a ‘healthy’ diet. Both diets made half of their calories made up from carbohydrate. For each diet, calories contributed by protein and fat were the same too (23 and 27 per cent) respectively. The overall GIs of the two diets were 40 and 59 respectively. The study lasted for 12 months.

A number of measures were taken as part of the study including body composition, sex hormone levels, and blood sugar control (as assessed with an oral glucose tolerance test).

Compared to the group eating the standard diet, those eating the lower-GI diet saw significant improvement in the results of the glucose tolerance test, which would point to improved blood sugar control and insulin action.

Also, 95 per cent of women saw improvement in the regularity of their menstrual cycle, compared to 63 per cent of the other group. Overall, the lower-GI group did better, in other words.

This study provides some objective evidence that a low-GI diet has merit for women with PCOS. However, my advice for women with PCOS looking to improve their condition through diet is not to eat a low-GI diet, but to eat a low-carb one. The thing is, it is possible to eat a low-GI diet and still eat a lot of carb. And, in essence, the less carb someone eats, the less insulin they secrete and, in theory at least, the better the result.

I used to be a fan of low-GI diets (and still am, on some levels). However, over the years I’ve become convinced that for many, low-GI diets just don’t go far enough. This is not just true for PCOS, but for other issues too including excess weight and type 2 diabetes.


1. Marsh KA, et al. Effect of a low glycemic index compared with a conventional healthy diet on polycystic ovary syndrome Am J Clin Nutr 19 May 2010 [epub before print]

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