Those late night cram-a-thons in college, the all-nighters you’ve pulled to meet a deadline at work—they’ve just never felt quite right unless you had heaping piles of chips, Taco Bell, cookies, and soda by your side, right? Stress, a lack of sleep, and deliciously terrible food choices are a threesome as inextricably linked as squats, deadlifts, and bench presses, and that’s not just because college students are known for cheap eats. A lack of sleep is directly responsible for a series of changes in the body and brain that quite literally drive you toward the junk food aisle.
Two studies have shed a lot of light on this time-worn truth. The first, from Columbia University and New York’s St. Luke’s Roosevelt Hospital Center, looked at 25 volunteers when they were getting a healthy 8 hours of sleep per night and again when they had been limited to 4 hours. In both cases, the volunteers were shown images of unhealthy foods like pepperoni pizza, cheeseburgers, and cake, alongside healthier foods like fruit, veggies, and oatmeal.
But the experiment was more complex than simply asking which foods the volunteers wanted the most, which is how some other studies have found a link between sleeplessness and junk food cravings. Subjects were actually hooked up to functional magnetic resonance imaging (fMRI) machines that tracked blood flow in the brain. The results were clear: On low sleep, brain networks associated with craving and reward—areas which might be characterized as more “base” and focused on short-term deliciousness over long-term health—were much more active, particularly when shown images of junk food.
The study’s authors hypothesized that when we’re low on sleep, we’re low on energy, so we may be naturally inclined toward high-energy (read: high calorie) foods. Lead researcher Marie-Pierre St. Onge told CNN that “the restricted-sleep brain reacts to food stimuli as though it (were) food deprived.”
The second study, conducted at the University of California at Berkeley, also used fMRI machines to show that sleep-deprived individuals—in this case, 23 students who had gone without sleep for 24 hours—have a heightened fondness for unhealthy food as compared to their well-rested selves. But this study also found that when subjects were sleep-deprived, the areas of their brains involved in using information and making rational, thoughtful decisions showed diminished activity.
Although they had slightly different results, the two studies are two sides of the same coin: A lack of sleep makes you less rational and more interested in short-term desire and immediate reward. And when you think about it, that’s the crux of the obesity epidemic: the deliciousness of unhealthy food provides a much more immediate reward than the long-term benefits of healthier food, like a trimmer waistline and a lower risk of chronic disease.
One might even argue that humanity’s difficulty with prioritizing long-term over short-term goals is the cause of most of our problems—so why make that challenge even harder with crummy sleep? A solid night’s rest keeps your wits about you, helps you think clearly, and literally stimulates your brain into making better, more rational decisions. Hit the hay and wake up wise: it’s the smart choice to make, for your waistline and your overall well-being.
 Shechter A, et al. Alterations in sleep architecture in response to experimental sleep curtailment are associated with signs of positive energy balance. Am J Physiol Regul Integr Comp Physiol. 2012 Nov 1;303(9):R883-9.
 Greer, SM et al. The impact of sleep deprivation on food desire in the human brain. Nat Commun. 2013;4:2259.
 Goldstein AN, et al. Tired and apprehensive: anxiety amplifies the impact of sleep loss on aversive brain anticipation. J Neurosci. 2013 Jun 26;33(26):10607-15.