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Sleep might help dieters shed more fat


woman sleeping, which might be key to helping body lose extra fatLaying up for a solid night's sleep might not sound like the best recipe for weight loss, but loads of research has pointed to the importance of sufficient shut-eye to losing weight. And a small new study shows that not getting enough sleep might severely cut into people's ability to lose extra fat. 

Researchers found that if dieters got a full night's rest, they more than doubled the amount of weight lost from fat reserves. So even though subjects lost about as much weight when they were sleep deprived as when they were well-rested, only about a quarter of the weight lost during the short sleep period was from fat. Tired-eyed dieters also reported feeling hungrier than they did when they had gotten enough sleep. Results of the study were published online October 4 in Annals of Internal Medicine.

"Cutting back on sleep, a behavior that is ubiquitous in modern society, appears to compromise efforts to lose fat," Plamen Penev, an assistant professor of medicine at the University of Chicago and study co-author, said in a prepared statement. Study subjects lost about 55 percent more fat when they got ample sleep at night.

For the study, 10 overweight volunteers (ages 35 to 49 with a mean body-mass index of 27.4 kilograms) started a personalized diet plan that reduced calories (to an average of about 1,450 per day) but maintained a sedentary lifestyle. For two weeks, subjects reported to the lab to spend 8.5 hours a night in bed (with an average sleep time of about seven hours and 25 minutes), and during a second two-week period—either three months before or after the 8.5-hour nights—the same volunteers were allowed only 5.5 hours a night in bed (with an average sleep time of five hours and 14 minutes).

During both study sessions, the subjects lost about three kilograms each. Nearly half of that (1.4 kg) was from fat when the volunteers were sleeping long, but less than a fifth (0.6 kg) of the lost weight was from fat when they got less than six hours of sleep. The rest of the weight was fat-free body mass, which includes other components such as water or muscle, and is generally not the target of those seeking to lose weight.

Food cravings and metabolism are controlled in part by hormones, such as ghrelin, which stimulates hunger and lowers energy use. And when the study subjects were getting less than six hours of sleep a night, their ghrelin levels rose from 75 nanograms per liter to 84 ng per liter. Levels remained steady when subjects got plenty of rest. The volunteers were on the same tightly controlled low-calorie diet during both phases of the study, and the weight- and fat-loss difference between adequate sleep and too little sleep might otherwise be even more pronounced, the researchers behind the study speculated.

So despite any extra calories a person might burn while burning the midnight oil, losing sleep is hardly the best way to lose fat, this study suggests. "If your goal is to lose fat, skipping sleep is like poking sticks in your bicycle wheels," Penev said. "One should not ignore the way they sleep when going on a diet." Plenty of other research also suggests that getting enough sleep is also crucial for good long-term health in general.

Image courtesy of iStockphoto/Mari

The views expressed are those of the author and are not necessarily those of Scientific American.

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