Really. There are foods that take more calories to eat than they provide, at least if you use the term food loosely. Celery, is a good example.
An 8-inch stalk of celery contains approximately 6 calories, but just digesting it will burn more than 6 calories, resulting in a negative caloric intake. Contrary to popular belief, chewing and swallowing the celery doesn't burn the calories, it's digesting the tough cellulose that expends the energy.
You can end up with negative calorie intake from cold diet drinks too. Your body burns calories warming the liquid up to body temperature--usually more than the few calories the drink contains. "Anybody for a cold one?" could be a dieter's rallying cry, but it won't work with beer.
Properly prepared cauliflower, cucumbers, spinach, and other veggies can cause your body to burn more calories than you ingest too. But celery with peanut butter or ranch dressing does not count as a negative-calorie food!