Yes. The colon reabsorbs water + a few salts back into the body, but all the nutrients will have been absorbed long since by the small bowel. People with diarrhoea-prominent IBS and ileostomies live a normal lifespan.
Diarrhoea caused by IBD is a different kettle of fish, because there you have an inflammatory component. The main danger of not treating IBD is that chronic inflammation could have long-term health consequences, far more so than the diarrhoea itself. In UC, the worst-case scenario is colon cancer. In Crohn's, the inflammation can go through all the layers of the bowel and cause strictures, abscesses and fistulas. Not to mention the systemic complications of inflammation such as fevers, anaemia, joint pain, increased blood-clotting etc.
Maybe in mild IBD none of the above might ever happen. But it is a gamble, and if you are newly diagnosed, mild disease might very well become severe disease over the next few years: mine most certainly did.
Post Edited (NiceCupOfTea) : 1/11/2014 8:59:54 AM (GMT-7)