I've heard recently that the causality for heart disease actually goes the opposite way than everyone assumed. The body's response to inflamed arteries is to lay down a layer of fatty plaques to protect the arteries from further damage. The fat deposition is the effect of the inflammation, not the cause, and now researchers are trying to understand just what the real cause is.

...which just goes to show how complicated causation vs. correlation is in real science. It was a pretty obvious conclusion that clogged arteries would cause heart disease...except that it's both obvious and wrong.