I don't have personal experience with this, but my best friend's Chow-Husky mix was diagnosed with IBD and the solution after extensive work with her vet was to put him on a diet with hydrolyzed protein (protein that has already been broken down, basically). She did a lot of online research on the available brands and settled on Purina HA, which doesn't have that nasty artificial preservative you want to avoid (its name escapes me at the moment). The ingredients are pretty gross when you read them, and the kibble looks like big Sugar Pops, but Hajime has been doing great on it for years -- no stomach issues, plenty of energy, etc. There are treats made in the formula too, as she has to be religious about not giving him anything else (except some PB for a pill he takes for another condition).