The major thing that sets kitten food apart is that it often has extra protein. Food for seniors can differ in a number of ways: - The individual pieces may be smaller, making them easier to digest. - Can contain fewer calories (as older cats are less active, they tend to put on weight faster) - Sometimes the amount of phosphorus in senior food is lowered, which can be beneficial for cats with kidney problems. - Food for seniors may contain extra meat to improve the smell. This helps by making the food more appealing to older cats that are losing their sense of smell.