If you break a fast in the middle of a healing crisis, you have an unhealed wound that will stay with you until you do another fast. The body opens up old wounds to repair them and if you don't let your body finish the job, the wound remains open. If he read a book on fasting (or was supervised), he'd know never to break a fast during a healing crisis.
This is why most experts say to start with short fasts and ideally do your first fast supervised.