I would avoid crunches and anything taxing to your abdominal, but I do exercise with mild-cronic ulcerative colitis, I've had it for 10 years. I ran a lot in highschool and continue to do so as long as my energy is good and I am not ill. Keep your exercise regimen simple to start, allow your body time to adjust to the new activity, and gradually add-in other aspects. I really enjoy pilates for muscle strength and long-distance running for cardio, but I've also done spinning (which targets every body area while being lenient to your abdominals). Good luck, work out when you feel well and sleep when you're tired - that's a biggie, too!
