Can adult cats eat kitten food?

Yes, of course. The nutritional needs of an adult cat and a kitten are the same, its just the amounts that should be fed to an adult or kitten that are different. For the most part, kitten and adult food from the same brand are the same, or at the very least, very similar in terms of ingredients and nutrients.

The biggest difference between the two is usually texture. Kitten food is usually softer in texture or has smaller pieces. Dry adult food pieces may be too big for a small kitten, but wet food can easily be mashed up in order to be eaten more easily. Some premium cat food brands are suitable for both adults and kittens and do not offer a "kitten" range.