Mostly, avoid poisonous things. Your body can, indeed, run well on starch. Should it? Nobody knows. I know if I were dropped in the woods today, I'd be eating tons of greens and medium-sized animals, some fruits and roots, and not much else. Extrapolate for different habitats and evolutionary history, and build your ideal diet on your ancestry and what you think they were best adapted to eat. And even then, with mutations abounding, it's still a roll of the dice.
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.