I think there are two main philosophies at play. Either you give the gut bulk through eating fiber, or you eat foods to maintain a fast transit time. I lean toward the transit time approach by eating plenty of easy to digest simple carbs. Personally I've never felt better.

I think eating hard-to-digest, crappy proteins(like all the protein added to shakes, bars, etc)... paired with fermentable bulk fiber... is actually the recipe for inflammation, irritation and colon cancer.