I've always been irritated that so much dog food is composed of stuff like corn and wheat flour. When have you ever seen any species of canine grazing in a field? They are carnivores. Recent genetic studies have proved that the domestic dog is not merely a close relative of the wolf, but in fact is a wolf, albeit a subspecies brought about through controlled breeding. Canis familiaris is now Canis lupus familiaris. And if you've ever watched nature documentaries about wolves, they are all about being carnivores.
Cats are even more meat-dependent. I don't know how anyone could get a cat to eat vegetable matter. They don't even have the ability to taste sweetness, because duh they're meat eaters.
I think this is why so many people have found success in the so-called Cave Man Diet. Primitive man ate meat and unrefined plant matter like fruits and berries.