I prefer to think of the macronutrient ratios of hunter-gatherers for inspiration. The body really can do fine on a wide variety of staple foods. There are pathways for both carbohydrate metabolism and fat metabolism and I think it prudent to train both pathways for efficiency. People eat everything they can find. Always have. Just stick to what they've been finding in the wild - and you're miles ahead of the rat race.
I'm a high-fat guy, but I'm also of European and Native American descent, with tendencies toward the autism spectrum - so ketosis is a happy place for me. That might not be true for everyone, so to assert "the body" has a "preferred" source is preposterous.
Steak, eggs, potatoes - fruits, nuts, berries and forage. Coconut milk and potent herbs and spices. Tea instead of coffee now and teeny amounts of kelp daily. Let's see how this does! Not really had dairy much, and gut seems better for it.