Standing in front of the vast selection of cat food available at pet-supply stores, you may feel you need a degree in feline nutrition to choose the appropriate food for your pet. Start narrowing down your choices by selecting from products appropriate for your cat's age. Many manufacturers have a food formulated for each stage of a cat's life: kitten, adult (regular and diet) and senior. Kittens, for example, need more protein and fat than adult cats, while older cats need fewer calories. 

If your cat has any health problems, this will affect your choice. An overweight cat can benefit from a diet food, but check with your vet before making a switch. If your cat is pregnant or has kidney or heart disease, your vet may suggest a special "prescription" diet available through the clinic. This may be temporary, although in some cases your cat will have to be on this food for the rest of his life. 

For the long-term health of your cat, a premium brand is worth the investment; ask your vet for some recommendations. You may want to alternate among a few of the high-quality brands, serving one kind for a couple of months, then changing to another. If your cat becomes so used to one type of food that it's all he'll eat, you'll be in a bind if ever it isn't available. But because cats' digestive systems can be delicate, radical changes of food may cause diarrhea. Introduce new food or alternate brands gradually, adding more of the new food while decreasing the proportion of the original food until the changeover is complete.