There may be a reason why you crave fries and other greasy foods the morning after a crazy night out: When you sleep poorly (it's inevitable after drinking a ton), sleep deprivation messes with your brain in a way that amps up your appetite for high-fat foods, according to new research recently published in the journal Scientific Reports.
In the study, researchers tracked 34 sleep-deprived men in a sleep lab for five days and four nights, monitoring them around the clock to observe what they ate. On the first night, everyone slept for eight hours, but they weren't permitted to sleep a wink during the next three nights. The researchers also monitored 12 guys who slept regularly throughout the study, and they administered daily MRI scans to monitor everyone's brain activity.
The sleep-deprived participants ate about 1,000 extra calories at night when they were awake. By day, they ate about the same number of calories as they'd eaten after a full night's rest, which means they didn't eat less to make up for the overnight surplus. Obviously, if you're awake for more hours, you have more hours to be hungry. But researchers noticed something more surprising: Sleep deprivation changed the kind of foods people ate. They consumed more calories from fat and fewer calories from carbohydrates.
The brain scans revealed why: Sleep deprivation super-charges the brain's "salience network," which connects sensory stimuli—like high-fat foods that look and smell delectable—to signals of pleasure, which ultimately guide your behavior. (Not surprisingly, obese people's brains tend to function this way on the regular, according to previous research.)
While eating some dietary fat is a good thing (and some people don't eat enough of it), fatty foods tend to contain more calories than carb- or protein-rich foods. Overdo it on the fries, and you could eat too many calories, overall. You know what happens next: Your body doggy-bags the leftover calories and stores them as fat, which can affect your health, not to mention your waistline.
But that's not the only problem: Experts already know that people who consume their calories late at night also tend to have a tougher time maintaining or losing weight, says study co-author Hengyi Rao, Ph.D., an assistant professor at Perelman School of Medicine at University of Pennsylvania. Because sleep deprivation promotes late-night eating, this can cause a vicious cycle.
That said, it'd be remiss not to mention that everyone in this new study had a penis. And researchers say men overeat to a greater degree than women during sleep loss. (Ha!) Still though: Sleep = good for everyone. Skimp on it, and you'll likely pay the price—in extra flab.
This article originally appeared on Cosmopolitan.com. Minor edits have been made by the Cosmo.ph editors.