There is no average size for bowel movements, according to Cleveland Clinic. Size, shape and consistency vary significantly among individuals. People should be concerned if they notice variations from their typical routines that do not go away quickly.
For instance, a change to very narrow stools sometimes indicates colon cancer because the disease causes intestinal changes, Cleveland Clinic explains. Another difference to check out is blood in the stool. This has several possible causes, including polyps, colorectal cancer, hemorrhoids and anal fissures. In certain cases, frequent diarrhea is a result of Crohn’s disease or ulcerative colitis. At the other extreme, constipation problems are sometimes brought on by narcotic pain medicines, iron supplements, dehydration or reduced activity level, reports WebMD.