28 yrs old, male. do narrow stools always indicate colon cancer or are there other reasons? no blood in stool. bloating and gas.

Not always: No, thin or narrow stools do not always indicate presence of colon cancer, but that is one of the causes. Partial bowel obstruction or other tumors can cause this as well, but these are worst case scenarios. Irritable bowel syndrome can also be a cause. If this happens sometimes it's ok. Consistent stools like this should be evaluated further by your doctor, especially if it's a change for you.

No – but what's up?: And narrowed caliber of stool can be commonly associated with colon carcinoma in any age group. It relates to the relative constriction of the rectum prior to evacuation. Other conditions include rectal stenosis, a sizable rectal polyp, or other conditions serving to narrow and constricted the normal sized stool. Best let a gastroenterologist evaluate you by colonoscopy and anoscopy.