Ask Dr. K: A little about iodine and your thyroid gland

DEAR DOCTOR K: I have irritable bowel syndrome. Can you explain what has caused it?

DEAR READER: The honest answer is we don’t know what causes irritable bowel syndrome (IBS). Over the past 20 years, we’ve discovered some clues and developed some new treatments.

IBS is a common condition. Symptoms include abdominal pain, diarrhea and/or constipation, bloating, gassiness and cramping. (On my website,, I’ve posted criteria that doctors look for when diagnosing IBS.)

No physical abnormality has been yet identified in people with IBS. For example, the walls of the large and small intestine appear normal. However, researchers have reported some abnormalities in how the intestines function.

Normally, the intestines move digested food progressively downward to the rectum, where a bowel movement removes it from the body. For that to happen, the walls of the intestine must squeeze down in a coordinated way. In many (but not all) patients with IBS, the movement of the intestinal walls is not well-coordinated.

Whether these abnormalities in how the intestines work explain the symptoms of IBS, however, remains uncertain. In fact, it’s likely that IBS is not a single disease, but rather a set of symptoms that stem from a variety of causes.

Some possible causes of IBS symptoms include:

— Infection. A bout of infectious gastroenteritis (stomach or bowel inflammation) may sensitize the gut in a way that leads to IBS symptoms.

— Overgrowth of intestinal bacteria in the small intestine. This may contribute to common symptoms in some patients, and antibiotic treatment may improve some symptoms.

— Unusual bacteria in the large intestine. In all of us, the large intestine is filled with trillions of bacteria, of thousands of different types. Some experts speculate that IBS may be influenced by the types of bacteria in the large intestine.

— Colon activity. Some research has found that muscle in the wall of the large intestine (colon) can become more sensitive than usual; it goes into spasm after only mild stimulation.

— Heightened sensitivity. Another possibility is that people with IBS have a much lower threshold for pain than people without IBS.

— Hormones produced in the GI tract, which affect movement of the bowels, may also trigger symptoms. Women with IBS often have more symptoms during their menstrual periods. This suggests that levels of reproductive hormones also affect IBS symptoms.

— Dietary factors. Certain foods can trigger IBS symptoms. Common culprits include cabbage, broccoli, legumes and other gas-producing foods, caffeine, alcohol, dairy products, fatty foods, raw fruits, and foods, gums and beverages containing sorbitol, an artificial sweetener. These foods contain substances called FODMAPs. It’s a matter of trial and error to determine which foods trigger your symptoms. Eliminate one food at a time to see which ones give you trouble.

— Stress and emotion. Stress stimulates colon spasms in people with IBS. Stress reduction, relaxation training and counseling can help relieve symptoms in some people.

I’ll bet that, like many illnesses, IBS has multiple physical causes and can be made worse by stress.

Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.

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