I could argue we are actually carnivores capable of imperfectly digesting an omnivore diet. You'll remain in perfect health eating just meat through gluconeogenesis, whereas carbohydrate foods are the root cause of most dietary issues. We can eat carbs and work with it but those foods are not optimal to the human body.
This is what I think also. Look at the digestive issues some plants give us. Like beans fermenting instead of digesting, and corn if not chewed well.
That goes against all the convention ‘wisdom’ of the four food groups, food pyramid, etc. But its a very interesting thesis and I am wondering if there are serious studies to show that. I have a family member who decided to go vegan several years back and I think she has suffered immune issues as a result, or at least partially as a result of that decision. I have been gently trying to persuade this person to reconsider the vegan lifestyle for health reasons.