I'm hoping for some good answers to this question too. I was told by the vet that Timber was underweight also, and he was on Zupreem, which was the only pellet he would eat according to his previous owner. I've tried Harrison's, Oven Fresh Bites, other Zupreem flavors, roundybush to no avail. The only thing he WILL eat better is nutriberries. Not ideal I know, but I'm more concerned about getting his weight up right now.