Fact: Your body knows the difference
The thinking here is that you're apt to dive into a big bag of M&M's when what you really need is to swig H2O. Reality check: Snack attacks are usually due to any number of reasons (boredom, habit, stress) besides thirst. In fact, “studies in animals show that being thirsty may actually make you eat less during the day,” says Rolls.
You're unlikely to mix up true thirst and hunger because the sensations aren't even similar. “They feel different and are regulated by separate mechanisms in your body,” says Rolls. When you're low on fluids, your cell and blood volumes decrease, and you get an unpleasantly dry, tacky-feeling mouth. Hunger, on the other hand, is driven by gut hormones, nutrients and glucose, and it's heralded by stomach rumbles and a sensation of emptiness.
Bottom line: Look out for the thirst and hunger cues above, and drink or eat up as needed. (And if what you're really feeling is boredom or stress, take a stretch break or watch some kitten videos instead.)