Great advice above. If it happens everytime, it's probably something food related. Maybe it's the surface you run on? Just a thought, but my training partner can only run on the trails or she has serious bowel/stomach problems. It's the surface that causes her agony- on the trails or soft surface she's fine- but put her on pavement or concrete and it's trouble-central down there. Doc said it's the pounding on the hard surface that "shakes things about" (obviously that's not the medically accurate explanation- just my summary). It's nothing she eats, just the surface she runs on. Probably isn't your problem, but again, just a thought.