We essentially did a vegan diet and then worked our way back up to meat to see the effects it would have on our health. What many don't understand about vegans and vegetarians is that there are lots of sources of protein. The only thing we found in the pure vegetable diet that we had to supplement was B12. There are other vitamins and minerals that are not as easy to get from veggies than from meat if you don't eat the right veggies, nuts, grains, etc., but I think a lot of people's understanding of veganism comes from what they've heard throughout their lives about eating meat to get your protein, which, of course, was pushed by the meat industry.
McCoy can do just fine on a vegan diet as long as he makes sure he's eating the right things to support his activity level, even if he has to take some supplements for some of it.