I just joined this forum looking for answers to a hip problem and ran across your post. I, too have Crohn’s disease and am a runner.. or a semi-runner who runs when the disease isn’t active.
I think the reason you’re not finding a lot of information on pre/post diet is because it’s different with each person. I find that raw fruits and vegetables don’t do well for me. Yogurt is great for people with Crohn’s. It’s also a good energy boost both before and after workout as it has both a protein and carbohydrate combination.
I do well with PowerBars. If I’m doing a long run, over an hour, I will eat half a bar about halfway through the run. Seems to work well.
Most of what you’ll learn is going to be trial and error. But keep in mind, carbohydrates are very important. When combined with protein and a little fat, give you the nourishment you need to get through and long and heavy workout.
Good luck and if you have any more questions, let me know.