Kittens have different dietary needs than adult cats and need to eat food specifically designed for kittens. According to the ASPCA, kittens require more energy than adult cats. Kitten food is designed to provide the proper amount of protein and nutrition to meet energy needs.
According to Pet Place, a kitten can safely begin eating adult cat food when it reaches 80 to 90 percent of its adult weight. Typically, kittens reach adult weight at around 9 months of age. It is best to introduce adult food gradually over the course of a week or so. Feeding increasing amounts of adult food while reducing the amount of kitten food is a good strategy to accomplish the change from kitten food to adult cat food.