moderato. adv. 1. (Music, other) at a moderate tempo. 2. (Music, other) (preceded by a tempo marking) a direction indicating that the tempo specified is to be used with restraint: allegro moderato.
While celery is a very low-calorie food, it likely doesn't provide you with negative calories. Mayo Clinic suggests that while it's theoretically possible for negative-calorie foods to exist, there are no reputable scientific studies that prove certain foods cause negative calorie effects.
It's not that the celery is difficult to digest, but rather it provides fewer calories than what is needed to digest it--so the overall effect is negative calories.. Keep in mind, the amount of calories you lose is very minimal. This is not the miracle diet food.