More evidence (should you require it) that supports the notion that fat doesn’t induce diabetes, but carbs can

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Variously on the site in the past I have attempted to highlight the science (never mind the common sense) that if you have diabetes and want to control it (or don’t want to get this condition in the first place), the part of the diet that generally needs reigning in comes in the form of carbohydrate (not fat). Diabetes is principally a problem of carbohydrate metabolism right. So, it makes sense that carb is the part of the diet that, primarily, diabetics need to be wary of, no? The carbohydrates most worth fingering in this respect are those that tend to cause substantial rises in blood sugar.

How disruptive a food is with regard to blood sugar levels is mainly determined by two things: the speed and extent to which it releases sugar into the bloodstream (its glycaemic index or ‘GI’), and how much we eat of it. Together, these two factors can are called a food’s ‘glycaemic load’ or ‘GL’. Basically, the higher the glycaemic load, the worse a food is for us (especially if we have diabetes and struggle with maintaining blood sugar levels in the healthy range).

With this in mind, I read with interest a study which assessed the relationship between dietary carbohydrate and risk of type 2 diabetes in women [1]. The study, published this month in the American Journal of Clinical Nutrition, assessed the relationship between a number of dietary factors and diabetes risk in more than 85,000 women over a 20-year period.

One of the dietary elements focused on in this study is what the authors termed the ‘low-carbohydrate-diet’ score. Basically, the less carbohydrate and more protein and fat individuals ate, the higher their score. The authors used this as a proxy for an individual’s adherence to the sort of low-carb diets (e.g. Atkins/South Beach/Protein Power) that individuals may have adopted in an effort to lose weight and improve their health. The basic question being asked by this study was, are such diets safe? Previous work by the same group had found that low-carb diets were not associated with an increased risk of heart disease (though some will insist that they are) [2]. Now, the authors were looking for any evidence that low-carb diets increased the risk of diabetes.

The long and short of it was that once ‘potential confounders’ such as body mass index and activity were taken into consideration, individuals with a higher low-carb-diet score were not found to be at increased risk of diabetes. Personally, the only thing I find in any way surprising about this finding is not that low-carb diets are not linked with an increased risk of diabetes, but that they appeared not to be associated with a reduced risk of this condition.

One of the criticisms I would have of the ‘low-carbohydrate-diet’ score is that it is a relatively crude measure of dietary quality. For instance, while it gives us some idea of what proportion of the diet comes from carbohydrate, it tells us nothing of the quality of those carbohydrates. And eating a diet very rich in white bread is likely to bring about quite a different result from eating a diet rich in broccoli, after all.

Fortunately, this study question collected and presented enough data for a more detailed appraisal to be possible.

In fact, this study analysed data relating to the glycaemic load of the diet and risk of diabetes. This is a good thing as the GL tells us not so much how much carb there is in the diet: it gives a guide to how much the diet is likely to upset blood sugar levels (which is far more useful).

And when confounding factors were accounted for, individuals with the diets of the highest glycaemic load were found to be about 2½ times more likely to develop type 2 diabetes compared to those consumed diets of lowest glycaemic load.

Analysis also revealed no link between animal fat intake and diabetes risk, and those with higher intake of vegetable fat were found to be at reduced risk of diabetes.

So-called epidemiological studies of this nature cannot be used to prove that a high GL diet causes diabetes. However, these findings are consistent with this notion. They are also consistent with, well, common sense.


1. Halton TL, et al. Low-carbohydrate-diet score and risk of type 2 diabetes in women. Am J Clin Nutr 2008;87:339-346

2. Halton TL, et al. Low-carbohydrate-diet score and risk of coronary heart disease in women. New Eng J Med 2006;355:1991-2002

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