They sell rat food, it comes in a canister or a bag and it is shaped like square blocks. I fed my rats "Exact hamster food" mixed with Lafebers Nutri Berries (a bird food) and an occational baby carrot. They should get a well known brand of rat or hamster food and watch the amount of veggies you give them. Too many veggies can lead to diarrhea. Avoide any types of lettuce and celery, as they have too much water and will cause diarrhea.

Cat food may be OK as an occational treat, but the protien is too high as a main rat diet. They should not get cat food, they should get either hamster food or rat-specific food (rat blocks).