If you're craving more calories after a sleepless night of work or play, it's no coincidence: Researchers from the University of Pennsylvania found that just a single sleepless night can hack your brain's response to food the next day, making you crave more of it than normal.
Dr. Hengyi Rao and his colleagues studied a group of 40 healthy people aged 21 to 50 who followed a pretty regular sleep schedule of six to eight hours a night. After sleeping soundly in a lab for about nine hours one night, Rao chose a group of them to stay awake on the second night then compared what both sleep and no-sleep groups ordered and ate from a menu. The team also took regular brain scans throughout the process. The sleep-deprived group ate almost 1,000 more calories than they usually would after the night of no sleep. They also ordered a lot more fat and less carbs than those who got sleep.
MRI scans revealed activity in the brain correlated with these new cravings; there was increased activity in what Rao calls your brain's salience network. According to Rao, losing sleep can hijack this pathway, which is known to influence your decision-making and behavioral responses. "Findings from our study have important implications for people who do not sleep at night, such as those who work the evening shift, night shift, rotating shifts, or other employer-arranged irregular schedules," says Rao. "Unfortunately, currently we do not know how to reverse the negative effects of sleep loss on brain function and eating behavior," other, of course, than to get more sleep.
The findings build on previous research about the possible neural mechanisms behind obesity and over-eating: Past studies show certain pathways in the brains of obese people are stimulated when they anticipate high-calorie food, compared to the lean and healthy. More work needs to be done on the subject, but now we know a little bit more about what external factors could be influencing these pathways. Of course, the study was limited in that it only looked at one night of sleeplessness rather than the effects of ongoing chronic sleep problems, but Rao thinks the same mechanisms for craving would be at play. And interestingly, if a messed up sleep schedule hijacks your diet, another study found it might also work in reverse: Changing your diet could actually put your circadian clock — or your body's sleep-wake cycle — back on track.