We Eat a Lot More When We’re Tired

Love it or hate it, sleep is an essential (and substantial) part of your life. When we don’t get enough rest, we start to break down—and so do our eating habits. A new meta-analysis [PDF] published in the European Journal of Clinical Nutrition found that sleep-deprived people ate hundreds more calories per day than they did when they were well-rested.

Researchers at King’s College London pulled data from 11 different sleep and eating studies on a total of 172 people. All of the studies involved an experimental group, in which people were kept awake for part of the night, and a control group, whose participants were allowed to get the sleep they needed. The participants’ energy intake—that is, how much they ate—and output (any physical exertion) were then tracked for the next 24 hours.

Unsurprisingly, sleep-deprived people did not exercise more than the well-rested. But they did eat more, averaging 385 calories over their typical daily intake. They weren’t just any calories, either; participants specifically sought out foods high in fat and protein. Their carbohydrate intake did not change.

What was behind these snoozy munchies? The research team can’t say for sure. Previous studies point to two potential culprits: our brains and our hormones. One 2013 report found that the brains of sleep-deprived people responded more urgently to pictures of fattening food, inspiring cravings even when the participants were full. And even as their snack-lust peaked, the participants experienced a drop in activity in the region of the brain associated with careful decision-making. They really didn’t stand a chance.

Other experiments have found that sleep deprivation can lead to an imbalance in the so-called hunger hormones leptin and ghrelin, which can trick the body into believing that it’s starving.

The takeaway from the latest study, say its authors, is that weight gain is complicated. Diet and exercise are crucial factors, but they don’t operate in a vacuum.

“Reduced sleep is one of the most common and potentially modifiable health risks in today's society in which chronic sleep loss is becoming more common,” senior author Gerda Pot said in a statement. “More research is needed to investigate the importance of long-term, partial sleep deprivation as a risk factor for obesity and whether sleep extension could play a role in obesity prevention."