If you want healthy then become a vegetarian. I went lacto veggie in 1983, then veggie in 1988, and finally vegan in 1989 (not raw...I just don't eat anything that has a brain or came from something that has a brain). I'm 55, but I have no problem keeping up with any average male in most sports...besting teens and twenties on many occations...after a couple of weeks of exercise (I sit on my butt too much as a computer engineer), and in 2007 after 5 years of solid study I earned a bachelor's degree in Computer Engineering with minors in Math, Physics, and Mechanical Engineering with many honor awards from CA State Univ - Sacramento which means my brain ain't in bad shape either.
I think the most significant metabolic change is that when I get hungry my stomach doesn't hurt...according to my research "hunger pains" are due to the meat eating bacteria that exist in a carnivor's intestines...when there's nothing for them to eat they will start eating the intestinal walls...gives a new meaning to Little Shop of Horrors doesn't it? Like the bacteria is saying, "Feed me or I'll eat you!"