On a 6 day fast I will lose 12 to 14 lbs, 8lbs of that is food still going through my gut 1 or 2 lbs is water and actual body fat lost is around 4lbs.
As soon as I start to eat again, the weight increases. I think its 4000 calories roughly in a pound of body fat, thats hard to burn 8000 calories a day lol.