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We all know we’re supposed to eat healthy portions. So why is it that a rough day at the office or even just the smell of chocolate-chip cookies can cause us to throw our best intentions out the window?

We tapped the nation’s leading experts for the unexpected reasons why so many of us overdo it—so you can break the cycle and prevent an unwanted pile-on of pounds.

1. You’re not getting enough sleep
Missing out on your zzz’s not only puts you in a mental fog, it also triggers a constellation of actual metabolic changes that may lead to weight gain. A lack of shut-eye harms your waistline because it affects two important hormones that control appetite and satiety—leptin and ghrelin—says Kristen L. Knutson, PhD, a research associate specializing in sleep and health at the University of Chicago’s Department of Medicine.

According to a study published in the Annals of Internal Medicine, people who slept only four hours a night for two nights had an 18 percent decrease in leptin (a hormone that signals the brain that the body has had enough to eat) and a 28 percent increase in ghrelin (a hormone that triggers hunger), compared with those who got more rest. The result: Sleep-deprived study volunteers reported a 24 percent boost in appetite. Short sleep can also impair glucose metabolism and over time set the stage for type 2 diabetes, Knutson notes.

How to get control:
When we’re exhausted, we hunger for just about everything in sight, especially if it’s sugary or high in carbs. That may be because these foods give us both an energy boost and comfort (since lack of sleep is a stressor), Knutson says. To quell the urge for fattening foods and still get the energy kick you need, reach for a combination of complex carbs and protein.

“If you’re feeling tired, you want carbs. But go for high-fiber carbs for long-lasting energy,” says Keri Gans, RD, a spokeswoman for the American Dietetic Association (ADA). “Fiber burns slower than simple sugars, and adding in some protein keeps you satisfied longer.”

At breakfast, have whole-wheat toast with egg whites or a high-fiber cereal with fruit and a yogurt. And for a food-free way to perk up during the day, take a 10-minute walk outside. You also can prevent uncontrollable cravings in the first place by prioritizing a good night’s sleep—get seven to nine hours a night in a slumber-friendly bedroom (one that’s as dark and quiet as possible and reserved for shut-eye and sex only).

A final tip: If you’re plagued by sleep problems, ask your doctor for a referral to a sleep specialist. Also, see Potential Side Effects of Sleeping Pills.

Next page: You’re sabotaged by stress