Well, yeah, insulin sensing leads to adipogenesis. Since the PPAR agonists increase insulin sensitivity, you're going to become fatter if you continue overeating. This sort of brings us back to the root cause of most DM (overeating). And while some of the PPAR agonists kill people, it does not seem to be a class effect; pioglitazone looks OK. (CHF is a class effect of the thiazoladinediones, but it's a more balanced tradeoff with diabetes.)