Earlier quoted context omitted.
I hope he doesn't damage himself Bad as it sounds, I hope he does. That would be the equivalent of "failing fast", I guess. Here's the worse outcome: he goes happily for some time, inspires some people to follow his lead, the group grows ... 5 or 10 years down the line - bam, they all end up with some irreparable damage to their health ...
What mechanism can you imagine that would produce such a nightmare scenario? Is there a fat-soluble (or otherwise stored) nutrient of which most human bodies contain a five to ten year supply? No I didn't think so. If Soylent Dude and his merry band of poor cooks can prove our current nutritional understanding wrong by dying five to ten years from now, then they should.
http://www.psychologytoday.com/blog/animals-and-us/201106/wh...
In her early 30's, Staci's health started going downhill. After twelve years of strict vegetarianism, she began to suffer from anemia and chronic fatigue syndrome, and she experienced stomach pains for two hours after every meal. "I was completely debilitated," she tells me. "Then I changed the way I ate."
The point here is not to bash vegetarianism, but to point out that it took her 12 years to develop health issues. And that's with vegetarianism, that is often considered a very healthy way to eat. So I would expect more potential hazards from something new, untried and untested.