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[Text: QQs: Do negative-calorie foods exist?]

Michael: It seems like a good idea: Food stores energy, what we call calories, but our bodies use calories to process food. So what if some foods have so few calories that we actually burn calories by eating them?

You’ll often hear people going on about these so-called negative calorie foods, celery, for example. But even though it’s theoretically possible, no known foods have negative calories. Including celery. You need calories for everything your body does, eating included. The process of chewing, swallowing, digesting, and absorbing food takes energy, in addition to the calories your body uses just keeping you alive.

The form of calorie burning that happens when you digest food is known as diet-induced thermogenesis, and on average, it uses up to 10 percent of the total calories your body burns each day. But even though your body needs to use energy to break down food, the whole point of eating, in an evolutionary sense, anyway, is to gain as much energy as possible, so you don’t use very much energy when you eat.

When your body digests fat, it burns up to 3 percent of the calories in that fat. It uses 5-10 percent of the calories in carbohydrates, and up to 30 percent of the calories in protein. And that’s the case for all foods, including celery. Sure, celery has a lot of water and indigestible, and therefore calorie-free, fiber, but your body also doesn’t use much energy to move that water and fiber through your system, since it isn’t digesting it. And celery also has carbohydrates, sugar, and a little bit of protein.

A large stalk of celery has about 10 calories, and you’d probably use around 2 calories to digest that stalk, meaning that you’d gain about 8 calories by eating it. So, celery is a very low-calorie food, and probably a good choice for a snack if you’re trying to eat fewer calories. But you can’t get rid of the calories you gain from eating a slice of chocolate cake by munching your way through a pile of celery stalks.

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