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.
Your points also go the other way. You are worried about flying fruits and vegetables around (Most food is transported by sea and road). What about basically unlimited access meat 24/7. That seems just as unnatural as out of season fruit.
With caveman hunting equipment, meat would have been difficult to come by.
Most of us are hardly eating native meats either. The farmed animals we eat have originated from all around the world.