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Study Shows Lack of Sleep May Prevent the Loss of Fat

Oct. 4, 2010 -- If your diet isn't going as well as you had hoped, the problem may not be your food choices or exercise habits. It may be your sleeping habits. Sleep loss may hamper even your best attempts to lose weight, according to new research in the Oct. 5 issue of the Annals of Internal Medicine.

Overweight adults lost 55% less fat when they got 5.5 hours of sleep per night, compared with when they slept for 8.5 hours a night, the new study showed.

"Sleep loss can prevent the loss of fat and make the body stingier when it comes to using fat as a fuel," explains Plamen Penev, MD, PhD, an assistant professor of medicine at the University of Chicago. Instead, the body burns off lean body mass, he says. The weight loss may be the same at the end of the day, but people who get adequate sleep lose more fat than their counterparts who are sleep-deprived.

"The sleep loss slows the loss of fat and speeds the undesirable loss of lean body mass, which doesn't help the body burn energy or calories," he says. "Sleep loss is accompanied by an increase in hunger that makes it less likely that you could adhere to diet."

In general, "losing weight becomes a more difficult fight when you don't get adequate sleep," he tells WebMD.

Sleep Loss Impedes Dieting Efforts

The new study of 10 overweight adults was conducted in two, two-week intervals. Participants ate a low-calorie diet and were scheduled to sleep for 8.5 hours per night for two weeks and for 5.5 hours per night for two weeks. Researchers measured their weight loss, loss of fat, and fat-free body mass.

During the longer sleep intervention, participants on average got about 7 hours and 25 minutes of sleep per night, while they slept for 5 hours and 14 minutes during the shortened sleep intervention.

Men and women lost 55% less body fat and were hungrier at night during the 5.5-hour-sleep weeks, the study showed.

Participants lost about 6.6 pounds during each two-week intervention. The main difference was in terms of fat loss. During the two weeks where they got adequate sleep, men and women lost 3.1 pounds of fat and 3.3 pounds of fat-free body mass (which was mostly made up of protein). By contrast, men and women lost 1.3 pounds of fat and 5.3 pounds of fat-free mass when they slept for shorter amounts of time, the researchers report.

Participants saw close to a 10-point increase their levels of the appetite hormone ghrelin during the two weeks when their sleep was restricted to 5.5 hours per night. Ghrelin levels rose from 75 nanograms per liter of blood (ng/L) to 84 ng/L, the study showed.

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