1. Creation viewpoint: If one takes the Bible literally, then it follows that all humans were vegetarian until the flood. In fact, Gen. 1:30 states that all creation ate vegetation. One could deduce also from the Bible that the carnivore/prey cycle is not God's original plan and that possibly it would be done away with in a paradise earth (Isaiah somewhere). So, it could be taken further that being a vegetarian today may be a bit of a moral issue and was a natural state of humans.
2. Evolution viewpoint: humans evolved from hunters. Humans were hunters and gatherers for eons. The only grains humans ate was what they found wild. Farming domesticated foods didn't occur for thousands of years. Humans evolved and existed by eating mostly animals and fish. They ate what vegetation they could find, but during the winters, they subsisted mostly on meat. Humans have not evolved any since Cro Magnon and therefore their bodies do much better feeding them what they evolved on: lots of meat and fish, fruits and vegetables.
So? What you choose to hold as true can influence your diet. It has made a difference in my dietary preferences going from one conviction to another.
Just some of my rambling thoughts. I don't intend this to be yet another creation/evolution debate; it's just a thought. Actually, it's covered in a few new books: The Omega Diet and The Omega Zone, for a couple.