digestive enzymes have been known by many to work. I don't know of any studies, I have seen minor ailments cured when someone couldn't properly digest a particular nutrient such as zinc from beef rather then overloading the person with 10 oysters.
If you get cramps when running you shouldn't try to rush the food through your system. If thats the case it was pointless to eat the food in the first place. Reduce your food intake to liquids before your run and eat well ahead of time. If it really annoys take note of how long before you run you eat each time and when you get cramps and when you don't. Then plan your meals accordingly.
As for fiber most people dont' recommend taking fiber before runs, or you'll be running to the stalls.