A new study explains why you crave junk food so fiercely when you're sleep-deprived.

Lack of Sleep Makes You Binge on Junk Food
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Pot smokers can blame marijuana for the munchies. For the rest of us, the problem may lie in a brain chemical called 2-AG (endocannabinoid 2-arachidonoylglycerol), which resembles chemicals found in cannabis and affects pain, pleasure, and appetite.

A new study published in the Journal Sleep found that our bodies usually have a low amount of this chemical overnight, and it rises during the day, hitting a peak in the early afternoon. But sleep-deprived folks experience higher levels of the chemical through the day, long past the usual 12:30pm peak.

In fact, tired subjects ate twice as much fat (in the form of snacks) compared to those who got eight hours of sleep. The study—led by Erin Hanlon, PhD, a research associate in endocrinology, diabetes and metabolism at the University of Chicago—focused on 14 healthy men and women in their 20s. The subjects spent four days at University's Clinical Research Center and either slept 7.5 hours or 4.2 hours. They all ate the same meals at 9am, 2pm, and 7pm. The sleep-deprived groups saw 2-AG levels rise to levels 33 percent higher than those who got a normal night's sleep—and the chemical remained elevated until about 9 p.m.

A related finding: The body requires about 17 calories to stay awake for an extra hour, which is about 70 calories over a four-hour period. But given the opportunity, sleep-deprived subjects ate 300 extra calories in a night-time binge.

The takeaway? Get sufficient sleep. And when you can't, avoid the vending machine at all costs. "If you have a Snickers bar, and you've had enough sleep, you can control your natural response," says Dr. Hanlon. "But if you're sleep deprived, your hedonic drive for certain foods gets stronger, and your ability to resist them may be impaired. So you are more likely to eat it. Do that again and again, and you pack on the pounds."