Heehee.
But not proven by you. You just took it as true on someone else's authority, didn't you? Don't you know you're not supposed to do that? ;)
It's *so* proven you, yourself believe it to be a proven fact.
Believing in something isn't the same as knowing it, now is it, Dom? You're supposed to be able to rationally know these things, but you don't. You read it somewhere, or your parents told you, or you learned it in school, but you don't really know it, and you certainly can't prove it - you just took it on authority, or on faith.
It's okay - so it's not humanly possible to be the sort of objectivist that Rand says you should be. So what? It's not the end of the world...
As it happens, I really do know two certain people: a sickly person who eats properly (according to modern nutritional ideas), and a healthy person who does not eat properly (ditto).
From this, I must conclude that your position vis a vis "good" vs. "bad" health is not objectively true in and of itself. We must conclude that this "objectivist" claim is at best incomplete.