I know you have him on a hypoallergenic diet....... but just wanted to throw out there, there is a new rx diet called Metabolic Diet made by Hill's... we have seen AMAZING results with weight loss on this food, and better yet, cats (and dogs) LOVE it. Owner compliance is usually the hardest thing with getting pet's to lose weight.... this diet is a God-send to the vet med world for safe weight loss in pets. And it's not a "starvation" diet, either, like all of the other weight-loss or light diets on the market today.