Be sure to read the ingredients before buying cat food. A good quality cat food should have a few key ingredients that make it delicious and healthy. The first ingredient is fat, which is a flavor enhancer. Fat is also important because it transports nutrients to cells and acts as a secondary energy source in times when protein is not in sufficient supply. Ideally, fat should account for 20 percent of your cat's diet. The next two ingredients are proteins and carbohydrates. These two elements are vital to the body's metabolic functions.