This is a question that puzzles me but the answer is probably known by those with a permanent ileostomy ......
UC often comes with watery stools that leads to weight loss and lack of nutrients.
What is the difference with the watery stools with a permanent ileostomy? Isn't everything moving just as fast as with UC, meaning weight loss and lack of nutrients?
I understand that more water than usual needs to drank and more salt consumed for the fact the colon isn't there to do that job.
To some extent the small bowel adapts and takes over the colon's role - it learns to absorb more water for example. (Though not as much as a healthy colon would.) The kidneys also adapt to some exent as well by becoming more efficient at conserving salt and water.
Secondly, food doesn't spend that long in the small bowel even in a healthy person - about
3-4 hours, maybe. It spends most of its time in the colon. For people with ileostomies, food doesn't travel through the small bowel any faster than before, unless they have lost some of their small bowel (often due to Crohn's).
The vast majority of people with ileostomies are not malnourished or underweight. However, it's not quite as simple as saying they are as healthy as people with intact colons on average, because that's not true either. Having IBD seems to complicate the matter still further. For example, even after colectomy bone loss is still common amongst ex-UC folks.
I couldn't actually find the article I wanted, which was published in the 2016 omnibus edition of the Ilestomy Association journal, so here's one I've posted before. It's about
j-pouch patients but I don't think that matters much - pretty much everything in it can be applied to ileostomates as well. www.ncbi.nlm.nih.gov/pmc/articles/PMC3424428/