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Chugging water

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Dietitians recommend staying hydrated all day long. "A lot of times we mistake hunger for hydration," says Shapiro. "For dieters, it's important to stay hydrated because then you'll know when you're hungry."

You can over-hydrate, but it isn't common, says Joy Dubost, RD, an American Dietetic Association spokesperson. Serious overconsumption can lead to a life-threatening condition called hyponatremia (symptoms include nausea, headache, and confusion).

The Institute of Medicine recommends women consume 2.7 liters and men 3.7 liters daily (about 11 and 15 glasses of water a day, respectively).

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