Fiber and fat slows down digestion
Agreed. Oatmeal helps digestion. The soluble fiber in oatmeal especially aids digestion and reduces constipation. Oatmeal is not quickly digested, and it is not recommended for the 24 hours before a colonoscopy.
I don’t think anyone says oats are “easy to digest”. If you look at food items that you should be eating before a colonoscopy for example it’s mainly stuff like white rice, white pasta, white bread, etc because these are things that are quick and easy to digest and won’t leave behind any difficult to digest grains/seeds/fiber/oats/etc.