That's funny, I was watching Food Detectives on the Food Network last night (shush) and they said that celery can be considered a negative calorie food. Celery only contains 8 calories, and you burn 5 calories by chewing, that plus the calories is takes to digest it is what makes it a negative calorie food. Or something like that.

But anyway, it's not enough to make a difference. Unless all you eat is celery, but that wouldn't be healthy.