What Is Ibs - Irritable Bowel Syndrome: Digestive Disorders

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What is IBS?

IBS usually begins in your late teens, 20s, or 30s. You're a relatively healthy person; then one day you begin to suffer intermittent cramps in the lower abdomen. You have to move your bowels more often than usual, and when you have to go, you have to get to a toilet right away. Your stools are loose and watery, possibly containing mucus. Sometimes, you feel bloated and full of gas.

After a while, the cramps return, but this time when you try to go to the bathroom, nothing happens. You're constipated. And back and forth it goes — diarrhea, then constipation, and pain and bloating in between. Some people with IBS alternate between constipation and diarrhea, while others have one without the other. Irritable bowel syndrome is the catchall term for this mixed bag of symptoms.

It's a common disorder, with no known cause. The most frequently reported symptom is pain or discomfort in the abdomen. People with IBS generally feel their pain subside after a bowel movement or passing gas. But they also may feel that they haven't fully emptied their rectum after a movement.

While some patients have daily episodes or continuous symptoms, others experience long symptom-free periods. These patterns make it hard to know whether someone has IBS or some occasional complaint that's part of the bowel's normal response to stress. Whether it is IBS usually depends on its frequency. The formal criterion for diagnosis is that symptoms have occurred for 3 of the preceding 12 months.

There's no organic basis for IBS. That is, there's no physical abnormality or disease at the root of the problem. And doctors don't regard IBS as a forerunner of more serious diseases, such as ulcerative colitis, Crohn's disease, colon cancer, or stomach cancer (see "Irritable bowel syndrome: What else could it be?").

IBS is a disorder in the functioning of the intestinal tract. Some experts suspect that it involves disturbances in the nerves or muscles in the gut. Others believe that abnormal processing of gut sensations in the brain may hold the key, at least in some cases. In addition, IBS can be triggered by a bout of gastroenteritis (stomach or bowel inflammation). Low-grade bowel inflammation may persist in these patients indefinitely, thereby leading to IBS. Other possible causes of IBS include emotional upset, stress, or other psychological factors.

Moving things along

Because the spasmodic pain associated with IBS seems to emanate from the colon, researchers have concentrated on this part of the GI tract, searching for any irregularities. The findings, thus far, have been inconsistent.

Colon motility (the contractions of the intestine's muscles and the movement of its contents) is controlled by nerves and hormones and by electrical activity in the colon muscle. The electrical activity acts like a pacemaker, similar to the mechanism that regulates the heartbeat. Movement of the colon propels the contents slowly back and forth, but mainly in the direction of the rectum. A few times a day, strong contractions move down the colon, pushing the contents ahead, and sometimes resulting in a bowel movement.

Some researchers have found that the colon muscle of a person with IBS begins to spasm after only mild stimulation. The colon seems to be more sensitive than usual, so it responds strongly to stimuli that wouldn't affect other people. Sometimes, the spasms lead to diarrhea; other times, to constipation. But some studies show that most of the time, colonic motor activity is no different for IBS patients than for anyone else.

Heightened sensitivity

Another possible explanation for these bothersome symptoms is that people with IBS have a heightened awareness of the inner workings of their gut. In several well-known experiments, balloons were inflated in the sigmoid colon, rectum, and small intestine of subjects. Those with IBS generally had a much lower threshold of pain than the healthy volunteers. Scientists believe that this lower pain threshold may be related to the dispatch of nerve signals from gut to brain.

Hormone and dietary factors

Hormones produced in the GI tract, such as cholecystokinin and motilin, have also been suspected of triggering IBS symptoms through their effects on bowel motility, but studies have not been definitive. Women with IBS often have more symptoms during their menstrual periods, suggesting that changes in reproductive hormones can increase IBS symptoms.

Certain medicines and foods trigger spasms in some people. Sometimes the spasm delays the passage of stool, leading to constipation. Chocolate, dairy products, or large amounts of alcohol are frequent offenders. Some people simply can't tolerate certain dietary substances — for example, lactose (a sugar found in milk), fructose (a sugar found in fruit and used as a sweetener), or sorbitol (an artificial sweetener) — and develop bloating and diarrhea as a result. Lactose intolerance is distinct from IBS, but the symptoms can overlap. Caffeine causes loose stools in many people, but is more likely to affect those with IBS. Bran and wheat flour may increase IBS symptoms. On the other hand, some believe that a lack of dietary fiber may contribute to IBS. Fat in any form (animal or vegetable) is a strong stimulus of colon contractions after a meal and can also contribute to IBS symptoms.

Stress and emotion

Stress is known to stimulate colon spasms in people with IBS. The process is not completely understood, but scientists point out that the intestines are controlled partly by the nervous system. Some studies have shown significantly higher stress levels among people with IBS compared with healthy individuals. And stress reduction or relaxation training or counseling has helped relieve IBS symptoms in some people.

Despite the influence of emotions, there's no evidence that IBS is an "imaginary complaint"; the symptoms are real and troublesome enough in many cases to warrant attention. But it does appear to have a psychological component. In other words, the gut-brain connection (see "The gut-brain connection") is very real. An emerging theory related to this connection focuses on the neurotransmitter serotonin. Neurotransmitters are chemicals that transmit messages between nerve cells. Like the brain, the gut produces serotonin, which in turn acts on nerves in the digestive tract. Some research suggests that IBS patients who suffer mainly from diarrhea may have higher levels of serotonin in the gut, while those with constipation-predominant IBS have lower levels.

Studies have found considerably higher rates of psychiatric problems among IBS patients than among healthy people or those with structural bowel diseases. Some 42%–61% of patients with functional bowel disorders who are seen in gastrointestinal clinics also have a current psychiatric diagnosis — usually anxiety or depression, according to one report.

Still, formal psychiatric care has not proved especially helpful for treatment of IBS, although sessions with a good therapist may help some patients manage their illness better. And such sessions could uncover and treat a problem with depression, for example, which may be either a cause or a result of the IBS.

Last updated:	August 21, 2007