I have those amalgams, can't afford to get rid of them yet. I think to expect a 13 year old to have the discipline to fast maybe is being too optimistic and she is still growing. I have visions of her talking to others saying mom put me on a fast. No food whatsover. People don't understand in general so you have to be careful there imho. If you found someone qualified to supervise maybe, but they are thin on the ground and would be expensive.