Losing sleep might make it harder to lose body fat

Even when cutting calories helps people lose weight, they may have a harder time getting rid of excess body fat if they don’t get enough sleep, a small experiment suggests.

Over eight weeks, researchers asked 15 overweight and obese adults to focus only on cutting calories and another 21 participants to both cut calories and get less sleep. Dieters in the sleep-restriction group lost about an hour of rest on each weeknight and then got an extra hour of shuteye on Saturdays and Sundays.

By the end of the experiment, people in both groups had lost about 7 pounds (3.2 kilograms). But in the sleep-restriction group, people lost less fat tissue and more lean muscle.

“People who want to lose weight, and lose fat in particular, need to avoid sleep loss during the week because you cannot make up for lost sleep on weekends,” said Kristen Knutson, a sleep researcher at the Northwestern University Feinberg School of Medicine in Chicago who wasn’t involved in the study.

“Of course, calorie restriction and exercise are both very important for weight loss and weight maintenance, but these results among others suggest that sleep also needs to be considered,” Knutson said by email.

Sleep deprivation has long been linked to an increased risk of becoming overweight or obese, and inadequate sleep has been linked to difficulties with weight loss, Xuewen Wang of the University of South Carolina in Columbia and colleagues note in the journal Sleep. Wang didn’t respond to emails seeking comment.

Most of the participants in the current study were women, and more than half were African-American. They were 45 years, old on average, and had a body mass index (a measure of weight relative to height) in the obese range.

Before the experiment, people in the sleep-restriction group said they consumed an average of about 1,775 calories a day, and during the experiment they cut back to an average of 1,454 daily calories. In the other group, people started out on about 1,575 calories a day and cut back to about 1,389 calories during the experiment.

Without sleep restriction, people typically got about 7 to 7.5 hours of sleep each night before the experiment and continued to do so once the experiment started.

In the sleep restriction group, people got about 6 to 6.5 hours of sleep on weeknights and about 8 to 9 hours of sleep nightly on weekends.

All of the participants picked up prepared lunches and dinners for four days each week and received sample meal plans and help from a registered dietician.

Among the people who didn’t cut back on sleep, a much larger proportion of the weight lost was in the form of fat rather than muscle mass: For half of this group, at least 83 percent of the weight they lost was fat tissue and less than 17 percent was lean tissue.

The people on sleep restriction tended to lose a higher proportion of lean tissue: For half of this group, at least 39 percent of the weight they lost was lean muscle and no more than 58 percent was fat.

One limitation of the study is that researchers relied on participants to count calories and accurately recall and report everything they ate and drank instead of having their intake measured by researchers for an exact calorie count.

Even so, the results add to evidence that good sleep habits may be a key ingredient for weight loss, said Marie-Pierre St-Onge, a nutrition researcher at Columbia University Medical Center in New York City who wasn’t involved in the study.

“Drastically cutting sleep has been shown to increase food intake and now there is increasing evidence that sleep loss can have counter-productive effects for weight management,” St-Onge said by email.

Ideally, people trying to lose weight should get about 7 to 8 hours of sleep each night, St-Onge added. More sleep than this isn’t necessary to lose weight, but people who typically get less than this may want to start getting more rest if they’re overweight or obese.

“If sleep is inadequate, this may be a reason for the extra weight,” St-Onge said. “To promote better sleep at night, shut down electronic devices a few hours before bedtime, dim room lights, avoid caffeine and other stimulants in the evening, set a cool bedroom temperature, reduce noise and get some exercise during the day.”