Lower-carb diet found to be better than a lower-fat one in pregnancy

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Pregnancy is a time when many women become a bit more focused on what they are eating. I recently had a conversation with a newly-pregnant women who was also a type 1 diabetic (a condition in which natural production of insulin is inadequate, necessitating the injection of insulin). She has found her way to a doctor who had advised her to eat a low carbohydrate diet which had been very successful in terms of controlling her condition and in reducing her need for insulin. Now she was pregnant, one of her questions was if it was safe to eat such a diet.

I, at the time, was not aware of any specific science on this. I did, however, point out that a low-carbohydrate diet was, essentially, no different from the sort of diet we as a species ate for the vast majority of our time on this planet. Plus, we do know of indigenous populations who eat relatively low amounts of carbohydrate who do not appear to have specific issues with regard to pregnancy or the subsequent health of their newborn.

This week saw the publication of a study in which a low-carbohydrate diet was tested in overweight or obese pregnant women [1]. Half of the group were randomised to eat a ‘low glycaemic load’ diet (45 percent of calories in this diet came from carbohydrate, with 35 and 20 per cent coming from fat and protein respectively). The other half was assigned to a ‘low fat diet’ (55 percent of calories in this diet came from carbohydrate, with 25 and 20 per cent coming from fat and protein respectively).

The chief outcome measured in this study was birth weight, and there was no difference here. However, the women who ate the lower carb diet had babies with larger head circumferences and had longer pregnancies too (both generally taken to be good things). Risk of pregnancy lasting less than 38 weeks was much lower in this group too.

In addition to this, the women eating the lower carb diet experienced, compared to the low-fat group, improvements in several markers of disease including levels of unhealthy blood fats known as triglycerides and an inflammatory substance known as C reactive protein. These changes would be expected to translate into a reduced risk of disease, particularly cardiovascular diseases such as heart disease and stroke.

The results of this study suggest that, overall, lower carbohydrate diets have benefits during pregnancy for both the mother and her child.


1. Rhodes ET, at al. Effects of a low–glycemic load diet in overweight and obese pregnant women: a pilot randomized controlled trial. Am J Clin Nutr (October 20, 2010)

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