Hard food packages do not mention starch or sugar. You have to subtract the protein, fat, fiber, taurine, etc to realize they are too heavily reliant on that corn or brown rice for kitty sustenance.
Again the Chicken model offers an alternative. Roast a chicken and enjoy it for your self and Rupert. No fish. Beef or pork if he takes it. They all love turkey. But, I never had luck with ground products. Even cooked to taste.
G'luck.
Moi
Lucky Rupert. Too bad about his long winters.