Get Some Sleep to Lose Weight, Researchers Say

On a diet but not seeing results? Your sleep habits could be to blame. Getting too little sleep could prevent dieters from losing body fat, according to a study published today in the Annals of Internal Medicine. Researchers observed 10 overweight men and women ages 35 to 49 who slept in a sleep lab for two separate two-week periods; participants logged 5.5 nightly hours in one of the trials and 8.5 nightly hours in the other. The dieters lost the same amount of weight during each trial, but when they were sleeping fewer hours, they lost muscle, rather than fat. Sleeping 8.5 hours a night, meanwhile, was associated with losing mostly fat. When sleep-deprived, participants had high levels of the hormone ghrelin, which triggers hunger and promotes fat retention. "The bottom line is that if people are trying to diet and lose weight for health reasons, it makes sense to get a sufficient amount of sleep," study author Plamen Penev told The New York Times. "If they're not getting enough sleep as they diet, they may have higher levels of hunger and be struggling to adhere to the regimen."

Sometimes it's impossible to get enough shut-eye, but there are ways to feel less tired and regain lost energy.

Sure, we all know we're supposed to get seven or eight hours of sleep a night, but all of us skimp from time to time, getting, say, five hours one night and six hours the next. Those lost hours, though, can add up to a big sleep debt by the end of the week—the reason so many of us feel wiped out by Friday, writes U.S. News's Deborah Kotz. But here's a bit of good news: Researchers have found that sleeping in after a few days of missed sleep can help pay back that debt, nearly erasing any lingering sense of fatigue and mental fuzziness, according to a study published in August in the journal Sleep. "The brain has a built-in reflex that helps you sleep deeper and longer when you're sleep deprived," says study coauthor David Dinges, chief of the division of sleep and chronobiology at the University of Pennsylvania School of Medicine. "This recovery sleep seems to have a genuine benefit to restoring alertness."

Think you're doing fine on only six hours a night? Think again. Although Dinges hears this from folks all the time, he says it's true for only a small percentage of the population. Most of us actually need seven or eight hours of shut-eye to feel 100 percent the next day. "If you fall asleep watching TV or struggle to stay awake in a meeting," he says, "you're sleep deprived." And it's not just fatigue you feel but reduced brain function in terms of your memory, alertness, cognitive speed, and reaction time. "Some of us are so used to not getting enough sleep that we've forgotten what it feels like to be fully alert," Dinges adds.

How much recovery sleep you need to feel recharged depends on how much sleep you've lost. In the study, volunteers were deprived of about three hours of sleep a night for five consecutive nights before being allowed to sleep for up to 10 hours. Those allowed to sleep a full 10 hours felt nearly, but not quite, back to normal the next day. Probably a second night of recovery sleep or an afternoon nap, would have helped them feel fully restored, says Dinges. Also clear from the study was that getting the advised eight hours of rest after skimping all week wasn't enough to pay back the debt. Those in the study who got that amount still felt exhausted the next day. [Read more: Sleep Deprived? Here's How to Recover.]