Celery is probably the most notorious "negative-calorie" food (that’s not actually a thing, by the way). What’s meant by the commonly used term? “There's this thing called the 'thermogenic effect of food'—in short, your body burns calories digesting the food you eat," says Angela Lemond, R.D.N., a spokesperson for the Academy of Nutrition and Dietetics. "But it really varies by person and genetics." So, yes, it could take more energy to digest than you’re actually getting from the veggie, which is where its reputation as a negative- or zero-calorie food comes from.