All I'll say is keep him on good food. Iams, Maximun Nutrition, Science Diet. the premium stuff. Not only does it take less to fill them (the cheap stuff is made mostly of ground corn and corn is not digestable so it doesn't fill them up) you have less to scoop and they stay much healthier.
Even the big name brands will use Corn meal, cround corn as a first ingredient. check the ingredient list. first listed is what is most in it. Even some lamb/Chicken and rice will have ground corn as the first ingredent.