What if veganism were unhealthy?

The following is an excerpt from an essay posted at the What's Wrong? blog:

I should say at the outset that I did not write this essay to convince you to be a vegan. Rather, I think a common objection to veganism raises an interesting philosophical question about killing in self-preservation or for the purpose of improving one’s life. Much has been written on killing in self-defense, but much less (to my knowledge) about the more general issue of killing a non-aggressor in order to preserve or improve one’s life.
A vegan diet is, for almost everyone, perfectly healthy. This doesn’t stop people from objecting to the claim that veganism is a moral requirement on the grounds that a healthy diet requires animal products. When I cover moral status and animal ethics in my bioethics and introduction to ethics courses, at least one student makes this objection each semester after being presented with arguments for the claim that most animals have moral status. Those of us who are not professional ethicists often have difficulty finding fault in such moral status arguments, and thus fall back on the health-based objection.[1] Clearly, then, the myth that veganism is unhealthy is as persistent and detrimental to the animal welfare movement as is the myth of “happy meat.”
Often, animal welfare advocates focus their energy on disabusing carnists of this notion.[2] They will point to the China Study[3], to their own years or decades long experience as a vegan, to the USDA’s and others’ remarks on vegan and vegetarian diets correlating with healthier individuals, to successful vegan professional athletes[4], and so on. This is all worthwhile and (somewhat) effective.
What I want to do, however, is consider what happens to the case for veganism if the health-based-objectors are correct. Suppose that being a vegan shaves a few years off of one’s life, keeps one from running as fast or as far, or lifting as much weight, as one otherwise might have had they consumed a diet which contained some meat, dairy, and eggs. What then?

See the rest here.