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This is Scientific American — 60-Second Science. I'm Karen Hopkin.

Few things are more satisfying than sleeping late on weekends. But though the extra z's may improve your mood, they do not appear to improve your health. Because a new study shows that so-called "recovery sleep" cannot reset² the body's metabolic³ clock...and may actually lead to some serious health issues.

"Sleep loss can impact a range of physiological⁴ systems. It can increase our risk for cardiovascular disease, it can cause weight gain, it can decrease insulin sensitivity, so it can increase our risk of diabetes⁵...."

Christopher Depner, an assistant professor in the department of integrative physiology⁶ at the University of Colorado, Boulder⁷.

"And this can happen, d?epending on what you're looking at, this can happen as quick as just one or two nights of not getting enough sleep."

A lot of us shut off the alarm on Saturday and Sunday. But we go right back to b?urning the candle at both ends once the workweek begins.

"So we were really interested in how the sort of cycle of between insufficient⁸ sleep, weekend recovery sleep, insufficient sleep, can impact your risk of obesity⁹ and metabolic disease."

Depner and his colleagues invited volunteers to a nine-day snooze-a-thon. One group was allowed to get a full night's sleep. The next was kept to just five hours each night. And the third group went back and forth¹⁰, restricted to five hours of shut-eye during the workweek, allowed as much sleep as they wanted over the weekend, and then back to five hours for the last couple days.

The results?

"Well, the key findings from this study show that when we maintain insufficient short sleep schedules during a typical work or school week, we find that this leads people to eat more than they need and this leads to weight gain. And when they are eating more, they actually eat more predominantly after-dinner snacks. And this altogether also leads to reduce the ability for us to regulate our blood sugar levels."

Ken¹ Wright, professor of integrative physiology at U.C. Boulder. He's the senior author of the study, which appears in the journal Current Biology.

So it seems a loss of sleep leads to a spike¹¹ in snacking. But even more surprising, sleeping in on the weekend doesn't help—and even makes things worse.

"We found that after the weekend, when they went back to getting insufficient sleep during the work or school week, we found that their liver and their muscle insulin sensitivity or blood sugar regulation was reduced. And this is not something we had found in people who maintained chronic¹² insufficient sleep schedules. So it's possible that, yes, this is a worsening of the body's ability to regulate blood sugar for those specific tissues after the weekend."

So make a date with a pillow. And trade the sweets for sweet dreams.

Thanks for listening for Scientific American — 60-Second Science. I'm Karen Hopkin.