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.
In brief: Probably. Celery is mostly fiber and water with little food content. It has been estimated that the calories expended in preparation, eating and digesting celeray are higher than the amount ingested by eating celery. Thus you can loss calories whilst filling yourself as long as you eat plain celery. Nothing untoward can come from eating celery.