I've got a slew of digestion issues and some metabolic problems (first ulcer at age 13). Pertinent info I've learned:

1) Diarrhea is a hell of a way to lose weight.

2) Treating your diet like a controlled scientific experiment does wonders. For about a year I never at more than 2 - 4 ingredients per meal (an ingredient being a single, unprocessed, whole food). That was a tough year, and my diet remains restricted due to what I learned, but the health I've earned is invaluable. What helps me is to think of food as a source of fuel, not pleasure.