Hi Linda, the Science Diet food is less calories per cup and a lot more fiber than Merrick so that would account for why he is hungry and pooping all the time. The one thing I would suggest is to put him back on the FortiFlora for a few days while you are changing back to Merrick. Even though he was eating Merrick before, there is a good possibility if you change the food too fast he will get diarrhea again and the FortiFlora should help prevent that. Since he is on medication for the rest of his life, it would probably help him to have the FortiFlora a couple of times a week, or give him a little kefir or yogurt a few times a week.
