My kitties eat Hill's Prescription Diet c/d because Mason has a bladder crystal problem, and HAS to have this, or the crystals will come back. It's too much of a hassle for me to try and feed the other 2 regular food, so to save money I mix the 20 lb bag with a 7 lb bag of super cheap Sport Mix. Mason is still getting the nutrition he needs and the other cats can eat the expensive stuff without making me go bankrupt!