I have been feeding both my cats with Natural Balance for years but, when they both developed urinary problems, I took my vet's advice and switched to Science Diet C/D, transitioning them from their old food. The first day they had the C/D exclusively the older female became lethargic and whiny, has diarrhea, and threw up five times before 1PM. The younger male cat couldn't stop eating it, and he already has a mild weight problem. I have never liked Science Diet because I felt it wasn't very good quality, but I didn't expect it to do this. I'm looking for a new food.