Eating celery results in negative calories. True.

Celery has about 6 calories per 8-inch stalk, making it a dieter’s staple. Although it’s loaded with latent energy, the amount we are capable of extracting from it is negligible thanks to the plant’s cellulose composition. Its ingestion can result in negative calories, but it is a fallacy to believe that effect has to do with energy expended in chewing. Though chewing might feel like a somewhat strenuous activity, it burns about the same amount of energy as watching paint dry. It is the bodily energy devoted to the digestion of the green stalks that exhausts calories…

Yet as enticing as all this sounds, the dietary bankroll built by this approach would be very small, probably amounting to no more than a few dozen calories a day. In a world where it takes 3,500 calories to work off a single pound of fat, feasting on celery would make only the merest difference…

But in defense of celery, we note that even if it doesn’t contribute mightily to a caloric imbalance which serves to work waistline magic, those who are eating it aren’t eating something else. Sometimes the key to a successful reducing plan is not so much the ingestion of “good” foods as it is the avoidance of “bad” ones. And it’s hard to sneak a chocolate bar into a mouth that’s busy chewing celery. [Snopes]