In my vet practice over the years I've been asked this question several times.
People want to be sure they are feeding their cat a healthy, nutritious diet that will help them have a wonderful and active life. (And I couldn't agree more!)
This response is what I give:
Cats prefer meat and do best with a canned or semi-moist diet. These diets are high in protein and fat, and usually less than 5% carbohydrates, which is ideal for a cat. Dry food is usually very high in carbohydrates which contribute to excessive weight gain.