I was a vegan for a while when I was in my late teens-early twenties. Now I'm 52 and have been "paleo" for 4 years. All my "numbers" as measured by medical science are perfect. Also, when I gave up grains, beans, dairy, sugar, and industrial seed oils, several lingering health issues disappeared, such as seasonal allergies (a.k.a. "hayfever"), afternoon tiredness/sluggishness, mental fogginess, and bowel issues. Never felt better.

Granted, I'm not perfect all the time: I still drink a beer every now and again, and sometimes eat corn and rice products. I stay away from wheat/gluten foods, however, as I am clearly intolerant.