What causes very long, tortious colon with slow colonic transit, per sitzmarks (over half left in 5 days)? does psyllium fiber cause redundant colon?

Yes: Fiber is healthy for general health and is helpful with colon function (i.e. Constipation). However, as with all good things there is another aspect. One side effect of a high fiber diet is enlargement and elongation of the colon. This can result in side effects like colon malrotation or torsion. Please know a low fiber diet leads to diverticula formation and the increased risk of diverticulitis.

Dr Korona agreed

Usually this is: Caused by chronic constipation and long term laxative abuse. Sometimes it is just genetic. Unless the bowel flips over on itself and obstructs or if dietary/ fluid management fail to resolve the constipation, surgery is not indicated.