 Does lack of sleep cause you to gain weight? Is there a connection between sleep and weight gain or weight loss? These next two videos will help answer that question. Population studies have found short sleep duration has been associated with obesity in both children and adults. Observational studies can never prove cause and effect, though. Maybe the obesity is leading to sleep loss instead of the other way around. Obesity can cause arthritis, acid reflux, and apnea, all of which can interfere with sleep. The relationship between obesity and sleep apnea, where you're breathing repeatedly, stops and starts throughout the night, may be explained by increased tongue fat, fat deposited inside the base of the tongue that may contribute to obstructing your airway when you sleep on your back. The reverse causation explanation of the link between obesity and inadequate sleep is bolstered by the finding that weight loss interventions can improve daytime sleepiness. Potential confounding factors also abound. For example, people with lower socioeconomic status often work less desirable hours, such as rotating or overnight shifts, or may live in noisier neighborhoods with poorer air quality, more crime. The link between inadequate sleep and obesity persists after controlling for these kinds of factors, but you can't control for everything. You can't know for sure if sleep deprivation leads to weight gain until you put it to the test. Have people pull an all-nighter and they get hungry and choose larger portions? Randomize people to shave even just a few hours to sleep off every night. They start eating an average of 677 calories more a day compared to the normal sleep control group. Other individual responses vary widely, anywhere from eating 813 calories less per day to as many as 1437 calories more. On average, studies found sleep deprivation led people to overeat by about 180 to 560 calories a day. Where strict people sleep, they also start craving unhealthier choices— more snacks, more foods that are fatty and sugary, strict people in a brain scanner after staying awake all night or after a few nights of 4-hour sleep, and their reward pathways light up brighter in response to high-calorie foods. Sleep deprivation bumps the levels of the chief endocannabinoid in the body, the natural chemical we synthesize that binds to the same receptors as the active ingredient in marijuana. This may help explain the nighttime nibbling. On the calories outside of the equation, some short sleepers may take the extra time to exercise. Others will be so sleepy they exercise less. The extra wakefulness may raise calorie expenditure up to about 100 calories a day, but if sleep-deprived individuals are overeating hundreds of calories, over time sleep deprivation may end up putting the wide in wide awake. With insufficient sleep inadvertently leading to such higher calorie intake, it's no surprise that 4 out of 5 studies involving as few as 2 to 5 nights of sleep restriction found an increase in body weight. In other words, if you sleep less, you may gain more. OK, but here's where it gets crazy. Even if you control calorie intake, you still lose more fat when you get more sleep. Overweight subjects, who normally got between 6 and a half to 8 and a half hours of sleep a night, were randomized to two weeks of either 8 and a half hours of sleep a night or 5 and a half hours of sleep, on the same calorie-controlled diet. Then the group switched and spent another two weeks in the opposite regimen, so they spent a month living in a lab so their diets and sleep could be totally controlled and monitored. And just looking at the scales, sleep duration didn't seem to matter. During both periods, they ate the same number of calories and lost the same amount of weight. But most of the weight lost while getting 8 and a half hours was fat, whereas most of the weight lost when only getting 5 and a half hours of sleep a night was lean body mass, same diet, but with more sleep. They ended up losing more than twice as much body fat, so you snooze, you lose fat.