Negative calorie foods ??

Hey all, Ive heard and known of the "Negative foods", where you eat these foods and its sooo low in calories that it takes more calories to digest and such that in the end your burning more calories than eaten, makin it a negative calorie food. With that said, I just want your thoughts and comments about this. Thnx a bunch, Robert =)

I have heard of celery being one of these foods, but didn't know if it was true. Looking forward to hearing other's comments on this! Lori