It depends on how you define "natural." In our hunter-gatherer days, it was very common to eat meat, and lots of it, since we did not have much caloric intake through plants alone. We see this today in certain tribal groups that still have that way of life.
That is to say, appealing to nature is not a good argument and is in fact considered a logical fallacy [0], because not all that is natural is good and not all that is unnatural is bad.
