Reviewed by Dr. Clement J. Cheng
Irritable Bowel Syndrome (IBS) is a common disorder of the intestines that leads to crampy pain, gassiness, bloating, and changes in bowel habits. Some people with IBS have constipation (difficult or infrequent bowel movements); others have diarrhea (frequent loose stools, often with an urgent need to move the bowels); and some people experience both. Sometimes the person with IBS has a crampy urge to move the bowels but cannot do so.
Through the years, IBS has been called by many names--colitis, mucous colitis, spastic colon, spastic bowel, and functional bowel disease. Most of these terms are inaccurate. Colitis, for instance, means inflammation of the large intestine (colon). IBS, however, does not cause inflammation and should not be confused with another disorder, ulcerative colitis.
The cause of IBS is not known, and as yet there is no cure. Doctors call it a functional disorder because there is no sign of disease when the colon is examined. IBS causes a great deal of discomfort and distress, but it does not cause permanent harm to the intestines and does not lead to intestinal bleeding of the bowel or to a serious disease such as cancer. Often IBS is just a mild annoyance, but for some people it can be disabling. They may be unable to go to social events, to go out to a job, or to travel even short distances. Most people with IBS, however, are able to control their symptoms through medications prescribed by their physicians, diet, and stress management.
What Causes IBS?
The colon, which is about 6 feet long, connects the small intestine with the rectum and anus. The major function of the colon is to absorb water and salts from digestive products that enter from the small intestine. Two quarts of liquid matter enter the colon from the small intestine each day. This material may remain there for several days until most of the fluid and salts are absorbed into the body. The stool then passes through the colon by a pattern of movements to the left side of the colon, where it is stored until a bowel movement occurs.
Colon motility (contraction of intestinal muscles and movement of its contents) is controlled by nerves and hormones and by electrical activity in the colon muscle. The electrical activity serves as a "pacemaker" similar to the mechanism that controls heart function. Movements of the colon propel the contents slowly back and forth but mainly toward the rectum. A few times each day strong muscle contractions move down the colon, pushing fecal material ahead of them. Some of these strong contractions result in a bowel movement.
Because doctors have been unable to find an organic cause, IBS often has been thought to be the result of emotional conflict or stress. While stress may worsen IBS symptoms, research suggests that other factors also are important. Researchers have found that the colon muscle of a person with IBS begins to spasm after only mild stimulation. The person with IBS seems to have a colon that is more sensitive and reactive than usual, so it responds strongly to stimuli that would not bother most people.
Ordinary events such as eating and distention from gas or other material in the colon can cause the colon to overreact in the person with IBS. Certain medicines and foods may trigger spasms in some people. Sometimes the spasm delays the passage of stool, leading to constipation. Chocolate, milk products, or large amounts of alcohol are frequent offenders. Caffeine causes loose stools in many people, but it is more likely to affect those with IBS. Researchers also have found that women with IBS may have more symptoms during their menstrual periods, suggesting that reproductive hormones can increase IBS symptoms.
