Walk through the pet supply store and you'll find a number of cat foods labeled "For Senior Cats." The ingredients list for these foods is slightly different than for the younger cats. Here are the important things to look for when picking out the best food for your aging cat. What Does and Does Not Change in the Older Cat's Body At all ages, a cat's body needs animal protein. It relies on the amino acids it gets from eating meat because it can't produce some of them itself.