Sleep deprivation feels as bad as it looks. Too little—as well as too much—shuteye can wreak havoc on your body. A morning glance in the mirror isn’t your only confirmation that this is true. New science is emerging that connects the amount you snooze with the amount of weight you gain.

“At one point, scientists started to realize that the obesity epidemic and the trend of people sleeping less were not occurring independently,” says Namni Goel, Ph.D., associate professor of psychiatry, Pearlman School of Medicine Division of Sleep and Chronobiology at University of Pennsylvania. It appears that when the hours we log at night are too little, hormones, metabolism, insulin sensitivity, decision-making skills, and waistlines pay the price.

How exactly does sleep debt affect the scale? When people don’t catch enough high quality zzz’s, the hormones regulating hunger, leptin and ghrelin, go haywire. Leptin is a hormone produced in fat cells that inhibits hunger and jumpstarts fatty tissue into burning energy. Levels plummet when you get less than seven hours of sleep a night, making your stomach feel empty even when it’s not. The hormone ghrelin is produced primarily in stomach cells, and levels rise with sleeplessness, stimulating hunger, slowing metabolism, and decreasing the body’s ability to burn fat. At the same time, there’s a rise in insulin resistance, a precursor for diabetes, and the stress-hormone cortisol, which can lead to excess abdominal fat. Even one night of sleep deprivation can set these into motion.


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Neurological research also shows that the sleep-deprived suffer from poor decision-making and higher level functioning, and on top of that, the brain’s reward receptors light up. A combined lack of willpower and a hyperactive reward center leads to an insatiable hunger for everything a person shouldn’t eat—cookies, ice cream, chips—before bedtime.

“There are consistent findings that most sleep-deprived people go for fats and carbs for late-night snacks,” says Goel, adding that there’s no definitive research as to why we crave these two food groups more than any other. “Everything comes together. Hormones that tell you you’re hungry with no satiety shut-off, consuming an extra 400 to 500 calories during a time of night when your energy expenditure is low and your body can’t process the food as well, and eating food high in fats and carbs.”

“There are consistent findings that most sleep-deprived people go for fats and carbs for late-night snacks,” says Goel, adding that there’s no definitive research as to why we crave these two food groups more than any other.

Even sleeping too much comes with its own risks. Epidemiological studies have shown that more than nine hours of sleep each night has been linked to an increased risk of obesity, cancer, and not enough activity. Though sleep extension studies are hard to implement because asking someone who normally sleeps the recommended seven to eight hours a night to add two hours to their sleep schedule isn’t always possible.

It’s equally as difficult to study people who say they don’t need more than four hours of sleep per night. Though Goel says researchers see an increase in slow wave brain activity during the time they sleep, it’s still not equal to the typical eight hours.


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“When we look at the performance of people in sleep-deprivation studies who say they are ‘used to’ four hours of sleep, we can see that they are not,” says Goel. “There’s no correlation between how people say they’re doing and how they’re actually doing. We’ve found those same people usually take a nap during the day or need stimulants like caffeine to substitute the sleep loss. And when we allow them to sleep in the study, they sleep 10 hours.”

If you’re unable to sleep regular hours because of shift work, a new baby, or an overwhelming class load, all is not lost. Goel says there are simple things you can do to keep from gaining weight. First, don’t eat after 7 p.m., even if you don’t go to bed until 11 p.m. or midnight. Feeding your body the amount of calories it needs during the day means your body doesn’t require those extra calories at night. If you’re feeling hungry in the evening, snack on healthy options like carrots or apples. Fruits and vegetables break down easily and won’t add significantly to your calorie intake. And when possible, make up for any sleep loss through naps or getting to bed earlier the next night. The more regular your schedule—sleeping and eating—the more likely your scale’s needle will stay put.

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