High GI diet leads to reduced fat-burning and increased fatness in mice

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As a general rule, scientists, doctors and dieticians subscribe to the view that when it comes to weight management, ‘a calorie is a calorie’. Essentially, this means that weight loss is the aim, we need to consume fewer calories than we burn, and as long as we do, then the form that these calories come in is irrelevant. Actually, as I pointed out in a blog post a few weeks ago, there is some evidence that the type of calories (irrespective of the number of calories we consume) we ingest may influence weight control. This blog post highlights a mouse study which found that low-carb diet brought about a similar level of weight loss similar to that seen in mice eating a standard diet of significantly lower energy content.

More recently, I noticed another mouse study which suggests that not all types of calories are created equal when it comes to effects that relate to body weight. In this study, mice were fed with diets of either high or low-GI (fast or slow sugar-releasing nature respectively) [1]. In each case, the mice were fed the same number of calories.

Feeding the mice the high-GI was found to down-regulate fat burning (fat oxidation) in the body compared to the low-GI diet. This difference was noted as early as three weeks after the experiment started. And as time went on, this effect appeared to contribute to other differences as well, namely higher body fat levels, as well as levels of fat in the liver.

Now, remember, the number of calories fed to these mice was the same. So, any differences between groups were the result of the dietary composition. Basically, the higher GI diet was found to reduce the metabolism of fat and lead to increased levels of fatness. It should perhaps be borne in mind that higher GI foods tend to cause more insulin secretion than lower-GI ones. This is relevant, as insulin has effects which impair fat metabolism while encouraging fat manufacturing by the body.


1. Klaus IF, et al. Impairment of fat oxidation under high vs low glycemic index diet occurs prior to the development of an obese pehnotype. Am J Physiol Endocrinol Metab 24 Nov 2009 [epub ahead of print]

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