To get to that point, the doctor will take a complete medical history that includes a careful description of symptoms. A physical examination and laboratory tests will be done. A stool sample will be tested for evidence of bleeding. The potential for abnormal function of the colon is always present in people with IBS, but a trigger also must be present to cause symptoms. The most likely culprits seem to be diet and emotional stress.
Many people report that their symptoms occur following a meal or when they are under stress.
No one is sure why this happens, but scientists have some clues. Eating causes contractions of the colon. Normally, this response may cause an urge to have a bowel movement within 30 to 60 minutes after a meal. In people with IBS, the urge may come sooner with cramps and diarrhea. The strength of the response is often related to the number of calories in a meal and especially the amount of fat in a meal.