Friday, January 13, 2017

Does exercising in the fasted state prevent weight gain?

The Study
Twenty-seven healthy male volunteers were overfed 30% of their body’s calorie needs for 6 weeks. During this overfeeding period, the men were randomized into one of three groups. Group #1 exercised early in the morning, before eating any breakfast. Group #2 ingested carbohydrate before and during their morning exercise. Group #3 was a control group that did not exercise. The two groups that exercised trained with identical programs (360 minutes of cycling and running per week). At the end of the 6 weeks, the control group gained 6.6 lbs. The group that exercised after breakfast gained 3.1 lbs. The group that exercised in the fasting state gained only 1.5 lbs. Journal of Physiology 2010; 588.21: 4289-4302.

Take Home Message
This is a very interesting study suggesting that exercising on an empty stomach may somehow protect us from weight gain. However, there is a major problem with this study that prevents us from drawing this conclusion with confidence. The study does not accurately measure, and does not provide for the reader, the number of calories these subjects consumed each day. The text of the article mentions that the energy intake in all groups was similar. This statement simply means that they were not significantly different statistically. It does not mean they were identical.

The difference in weight gain between the two groups was 1.6 pounds over 6 weeks, which equates to 133 calories per day. It may just be that the fasting group ate a tiny bit less than the breakfast group. The problem is that we don’t know what the difference was in calories per day. Therefore, it is impossible to conclude that exercising on an empty stomach has an impact on weight gain. However, this study has certainly generated an interesting hypothesis that should be tested with an intervention more sensitive to the caloric consumption of the participants. At the very least, this study shows us that exercising for an hour a day helps to prevent weight gain when overeating.

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