There was recently a post here on HN that relates to this. As a UC sufferer I found it very interesting.

> How the Gut's "Second Brain" Influences Mood and Well-Being (2010) (scientificamerican.com)

https://news.ycombinator.com/item?id=7957057

It has often been noted that "stress or feelings of anxiety, guilt or resentment seem to trigger the symptoms":

http://www.mckinley.illinois.edu/handouts/irritable_bowel_sy...