Poor Bear, glad to hear he's okay though. See I have a lab and gaining weight has never been a problem for her (it's genetic she gets it from my side of the family
). I have to agree changing foods would likely just cause trouble. If it's kibble do they sell canned, you could maybe add a bit of the same brand canned to his food. Of course you then risk him turning his nose up at the kibble when you stop the canned. I've heard great things about satin balls too but never had to use them.