The latest addition to an effective weight loss plan: a good night’s sleep.

Getting 8 instead of 5.5 hours of sleep a night appears to help promote weight loss, according to a new study in the Annals of Internal Medicine. The study was tiny – including just 10 participants – but its general conclusions are supported by other research.

“There’s a growing body of knowledge that’s relating short sleep with increased obesity and poor weight control,” said Dale Schoeller, professor of nutritional sciences at the University of Wisconsin, who helped design the study.

The research was conducted under very artificial conditions, with participants living in a lab and cut off from the world for two weeks. That’s why Schoeller is hesitant to brag about its key finding: Sleeping 2.5 hours more a night burns 400 extra calories a day – roughly as much as an hour of reasonably fast running.

“I don’t feel confident calling it 400 [calories]. I feel confident saying there’s a caloric advantage to getting enough sleep,” Schoeller said. “I could say maybe a couple of hundred [calories].”

Yes, you read that right: you can burn more calories by sleeping than by staying up late (and probably snacking).

The advantage to this study design, Schoeller said, was that researchers were able to carefully control the number of calories participants consumed, to be sure that both those who had short nights of sleep and those who stayed in bed for a full 8 hours ate the same amount. In previous research, Schoeller and his colleagues had shown that people who sleep less tend to snack more when given the opportunity.

Schoeller said he and his colleagues were surprised by their finding that short sleepers not only lost less weight but lost less weight from fat – which is bad for dieters. The body regains weight lost from protein and water faster than weight lost from fat, he said.

Everyday Health expert Dr. Caroline M. Apovian, director of the Nutrition and Weight Management Center at Boston Medical Center, said that these results – which she’d like to see confirmed by future research ¬ – suggest that lack of sleep alters the body’s hormonal balance.

“It could be that if you’re not sleeping, your body may think that it’s under stress, so it wants to restore your body fat. It might have to do with insulin resistance increasing, which leads to more storage of body fat,” she said.

In any case, the study and others like it are a reminder that being healthy involves more than just counting calories. The average American watches three to four hours of TV a night, said Apovian, also an associate professor of medicine at Boston University School of Medicine. Instead, she said, we should spend one hour of that TV time exercising (in front of the TV is fine) and another sleeping.