IBS can cause periods of diarrhea or constipation in different people. Mine was diarrhea.

Fiber can firm up loose stools and help diarrhea.

Diverticulitis is even worse. balloons leading off of the sigmoid colon that get filled with feces and cause pain and infection. (Diverticulitis) If they burst it causes peritonitis, infection in the abdominal cavity. Doctors recommend removal of the last 18" of colon as the only cure.

Plenty of fiber will prevent Diverticulitis from developing and help it if it is already present.

If you already have Diverticulitis, avoid eating popcorn. Warnings about eating seeds and nuts are false