I have seen a few people here mention that Water Fasting slows your metabolism.
I asked the fasting doctor and he said that is bs.
The reason they put weight on faster is that the body is cleaner and can get more nutrients out of food therefore requiring less food.
Eating the same amount as you did before a fast will cause you to gain weight faster, not because your metabolism has slowed, just because your body needs less food than it did before.