Bile acid malabsorption (BAM) often occurs alongside collagenous colitis, it produces a similar form of diarrhoea. BAM can be diagnosed by use of a SeHCAT scan which is described in Symptoms topic of the Guts UK! website.
Thus, it is possible is bile acid is a noxious factor. This concept is supported by the fact that budesonide reduces bile acid malabsorption.