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Mental Drain and Weight Gain

Thinking too hard and sleeping less can leave you reaching for high-calorie snacks that pack on the pounds.

Why is it that a big bowl of pasta calls out at you from the fridge when you're tired, stressed out, or working late? Though exhaustion can certainly wear down willpower and make comfort foods seem like a well-deserved luxury, there's more to the connection between fatigue and overeating than meets the eye. Researchers are uncovering why a little bit of fatigue can lead to a lot more nibbling.

Circadian Rhythm and (Diet) Blues

We definitely snack more when we're sleepy. A University of Chicago study found that after two weeks of sleep restriction, normally healthy eaters ate an average of 200 more calories a day, all in snacks. These munchies were often high in carbohydrate content and were usually consumed between 7p.m. and 7a.m.—the worst time, waistband-wise, for needless eating.

Late-night chow downs were also a habit among mice whose internal clocks were disturbed. With their circadian rhythm out of whack, the mice slept little, snacked when they should have been sleeping, and put on weight even when they were given the same food choices as normal mice. Diet and sleep is a two-way street however, suggests a Northwestern study.

Mice fed a high-fat diet slept poorly when compared with their healthy eating equivalents; this suggests that poor eating and poor sleeping might form a self-perpetuating cycle. A six-year Canadian study showed that over-sleepers and under-sleepers—people who slept nine hours or more as well as people who slept seven hours or less—put on more weight than peers who slept between seven and nine hours.

What's going on with your appetite when you're sleep-deprived? The answer lies partly in the body's chemical messengers. When sleep is disturbed—even for just two consecutive nights—your body makes more ghrelin, a hormone that stimulates appetite, and less of its counterpart, the appetite controlling leptin. Chemical changes aren't the only factor in play however. And a lack of sleep isn't the only snack-boosting factor.

Freshman Fifteen Reexamined

Overtaxing the brain can spark overeating in the same way that sleep-deprivation can. After a 45-minute session of cognitive work, college students given access to a buffet lunch ate 250 more calories on average than students who spent that 45 minutes listening to music. This suggests that even a simple cramming session is enough to cause an immediate increase in caloric consumption, a frightening prospect for students and workaholics alike.

While chemical changes appear during sleep-deprivation, this immediate increase in eating was not accompanied by any changes in appetite markers. Then why the post-test chow down? Researchers hypothesize that we instinctually reach for food, especially carbs, when fatigued because they are the most accessible form of energy. Since carbohydrates spike blood sugar and boost short-term energy, that bowl of pasta looks mighty good. But you're not carbo-loading for a marathon, you're just trying to stay awake. Unfortunately, those working away at cognitive tasks don't burn any more calories than their counterparts who are chilling out. It's no surprise when that bowl of pasta shows up on the scale.

Finally, Take a Break

Getting more sleep is a great way to curb a tendency to snack too much. And during those inevitable moments of fatigue, instead of going for a candy bar-induced energy boost, get your blood pumping with jumping jacks or a set of push-ups. Or just take a few deep breaths: The flood of oxygen to your brain acts as a natural energy boost (that's why we yawn when we're tired). It's rest your brain is craving, not last night's leftovers.