Some good comments in this thread, I really like where it is going. let me respond to each one that caught my interest,
I would have to agree with that to a certain degree, however species do evolve to have a specific diet, almost every animal is 'designed' or has 'evolved' to eat certain things and to not eat certain things.
Horses/deer/rabbits will eat meat if survival depends on it or even if the opportunity arises, but it is not optimal. Humans will almost eat anything in a life and death situation, but I am certain there is an 'optimal human diet', I don't know what it is but I am 110% certain that it does not involve flying out of season fronts and vegetables around the world.
Agree 110%, there are no essential carbs, or grains, there are however lots of essential amino acids and fats though.