The biggest difference between cat food and dog food is the amount of protein in cat food. Cats are strictly carnivorous, meaning their bodies are meant to eat meat, meat and only meat. Believe it or not, dogs are omnivores, so their bodies are equipped to digest meat and plants, and they actually need plants to keep healthy. Cat food, even kibble, has an incredibly high protein content which both makes it delicious to your dog, and may upset his stomach.