A study published last week in the journal Obesity may make you question whether you really want to rely on the Atkins or South Beach diets to reach your New Year’s Resolution goals.
It is widely believed that low-carbohydrate, high-fat diets support weight loss in most individuals and indeed, there is a good amount of research to back this claim. Despite this, few studies have examined the after effects of a low-carb diet, particularly once normal eating is resumed.
In a new study, scientists had rats consume either a regular high-carb diet or a low-carb, high-fat diet for sixteen days. After this period the diets were switched and rats were maintained on the opposite diet for another sixteen days. Both diets included the same number of calories, so the only difference between the groups was the relative percentage of macronutrients.
As you might expect, while the rats were fed a low-carb, high-fat diet they lost weight compared to rats on a regular diet. Interestingly, however, despite this loss of body weight there was little to no loss of fat, and therefore the rats that lost weight had a relatively higher body fat percentage than the rats fed a normal diet.
The low-carb rats also had lower energy expenditure (exercise and calorie burning) than rats on a normal diet, and the decrease persisted even when the animals were returned to a normal diet. This is consistent with reports of exhaustion in humans undergoing very low-carb diet regimens.
Furthermore, animals that were temporarily put on a low-carb diet regained more weight than animals that were never fed a low-carb diet. This suggests that short term exposure to a low-carb diet increases risk of weight gain compared to no dieting.
Uh oh.
According to this research it is possible that a low-carb diet may actually cause you to gain weight in the long run. How very unfortunate.
But while these results are compelling, do not go stocking up on pasta just yet. First remember that these are rats, not humans. The way scientists change the composition of a rat’s diet is by giving them different pellets of bizarre lab food with various proportions of “nutrients.” This is not the way humans eat (assuming you don’t spend too much time in GNC), nor can it ever reflect a healthy human diet. It would be great if they could put the rats on a diet of seasonal fruits and vegetables, whole grains, legumes and fatty fish, but that is not the way animal research works. This is something to keep in mind whenever you hear about nutrition studies.
Also, nutrition research using rodents rarely distinguishes between the qualities of different macronutrients. For example, did the “high-fat” diet contain mostly saturated fat, trans fat, monounsaturated fats, polyunsaturated fats or all of the above? A similar question can be asked about the quality of carbohydrates, but it is difficult to imagine high-quality carbohydrates coming in pellet form. A huge body of scientific literature suggests that the quality of different macronutrients is far more important to health and weight than relative proportions of refined macronutrients.
Protein is another question mark in this study, which the authors acknowledge. The low-carb diet they used was not high in protein like a typical Atkins style diet. However, their findings were similar to studies that did use higher protein content and their animals were fed sufficient protein to maintain normal body growth, so the effect of protein on their findings is likely to be small. Their goal was to examine the effect of extreme carbohydrate restriction, and this was accomplished.
Regardless of this study’s imperfections, the results shine an interesting light on our current understanding of how relative proportions of dietary macronutrients effect body composition, long-term body weight and metabolism.
Have you experienced weight gain after going off a low-carb diet?
UPDATE: This article is also available at Synapse.
Tags: body fat, low-carb, Obesity
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