There are two forms of fiber: soluble and insoluble. Soluble fiber, which can be found in beans, fruits, and oats, dissolves in water. Soluble fiber is helpful for people who are experiencing diarrhea or constipation from irritable bowel syndrome (IBS). Insoluble fiber, which can be found in whole grains and vegetables, does not dissolve in water. Insoluble fiber tends to make stools looser, which can be problematic for people who already have diarrhea.
Fiber may trigger symptoms in some people with inflammatory bowel disease (IBD). Sometimes a low-fiber diet is recommended for people with IBD, especially during a flare-up or after surgery.