Dogs eat cat food for a simple reason: dogs find cat food to be an appealing delicacy that is difficult to resist. If Rover is stealing Miss Kitty's food though, you may want to take some steps to discourage this behavior. While it's still nutrition, dogs are built differently than cats and therefore have different nutritional requirements. Not to mention, it's not nice for your dog to deprive your cat from needed nourishment, and secondly, consider the fact that cat food can cause problems to your dog, especially when consumed frequently or in abundance.