Task: Question Generation
Input (English): Foods that are claimed to be negative in calories are mostly low-calorie fruits and vegetables such as celery, grapefruit, lemon, lime, apple, lettuce, broccoli, and cabbage. There is no scientific evidence to show that any of these foods have a negative calorific impact. Celery has a thermic effect of around 8%, much less than the 100% or more required for a food to have ``negative calories''. A stalk of celery provides 6 calories to the body, but the body expends only half of a calorie digesting it. Even proteins, which require the most energy to digest, have a thermic energy of only 20%--30%.
Output (English): is it true that celery has negative calories?