I agree, Man is designed to eat meat, veggies, nuts, some fruit and to drink good, clean water. When I follow this plan I feel great and stay healthy, when I stray I fall apart at the seams. (I'm learning.)
What would happen if you put a Tiger shark on a tofu diet? Or a cow on a liver and onions diet? They would get sick and fat, be subscribed Lipitor and then die.
I've never known a healthy vegan and I have known a few. They've all been gaunt, weird and weak. We weren't created to be weak.