What kind of food should a cat eat?

Cats are obligate carnivores. This means the main ingredient of a cat's diet must be meat. Cats cannot synthesise several amino acids such as Taurine, so get all their nutritional needs from raw meat, organs and bone. Without meat, a cat would develop heart, eye and possibly kidney problems; they should not be on a vegetarian diet, or on a diet that has a large amount of grains or cereals.

The best possible foods for a cat is raw meat, bones and organs. However, if this is not possible, then premium brands of cat food are the next best thing as they supply everything a cat needs. Premium brands often have a high named meat content (labelled as Chicken, Turkey, Tuna, etc.) as the first, or first three ingredients. This is the best food you can feed your cat. It is wise to keep away from cheaper cat foods that have grains, corn, cereals and glutens on the Ingredients list - these are used to bulk out the foods and have no nutritional value to a cat whatsoever.
Wet food with these specifications are much easier to find than in dry food.

The amount of moisture in cat food is also very important. Dry food contains no moisture, so is quite dehydrating. Cats are notoriously bad drinkers because they have evolved to get all their needed moisture from their prey (their ancestors were cats that lived in very dry and arid environments where water was hard to come by), so therefore have a low "thirst drive" and will not often seek out water on their own. This is a trait that has been passed down over the thousands of years.

Canned or pouched food has anywhere between 60% to 80% water. Seeing as in the wild a cat's prey is around 65%-75% water, wet and raw food provides a cat with more than enough water each day.