When you start eating after a fast your metabolism will be extremely sluggish. To "kickstart" your metabolism I suggest only eating until you have a feeling of not being hungry (not to be confused with full). You will not be able to eat much at all for awhile. Also excercising regularly after the fast will speed up your metabolism as well. In my experience you will be back to normal within a month. However, you want to keep a reign on your eating after that point and try not to overeat to the point of being full. Of course you also want to eat the correct foods.