What Causes Irritable Bowel Syndrome?

Q: I suspect my abdominal discomfort, bloating and irregular bowel movements are due to irritable bowel syndrome. What causes that?

A: At best, irritable bowel syndrome (IBS) is inconvenient, forcing people to shape their schedules around their bathroom needs. At worst, it can be incapacitating, causing extreme distress and controlling people’s ability to work and travel.

IBS is what doctors call a functional bowel disorder, since it affects the way the digestive system works but isn’t due to any apparent structural problem. The cause of IBS remains frustratingly unclear, but symptoms are believed to stem from any of a wide range of factors. Among them:

Possible causes of an irritable bowel

Changes in the gut microbiome

This array of microbes in the gut is influenced by what we eat and drink as well as by illness. About 10% of people who develop a gastrointestinal infection, whether viral, bacterial or parasitic — even COVID-19 — show a higher rate of IBS.

Skewed intestinal muscle contractions

Normally rhythmic, these contractions push food through the digestive tract faster or slower than normal in IBS patients.

Faulty nerve signals

Normal digestion relies on clear communication between the brain, gut, and nervous system. These signals are disrupted in IBS.

Pelvic floor problems

This is especially true for women whose pelvic muscles don’t relax normally, which can lead to chronic constipation.

Early life stress

This can include traumatic events during childhood.

Genetics

People with a family history of IBS are more likely to have it as well.

IBS is categorized into three types according to which symptoms dominate: diarrhea (IBS-D), constipation (IBS-C), or a combination.

IBS management starts with diet and life-style changes. For many people, avoiding trigger foods, eating more fiber, drinking plenty of fluids, exercising regularly, and getting sufficient sleep can help control mild symptoms.

Symptoms may also worsen depending on the foods you eat. Wheat, dairy products, citrus fruits, beans, cabbage and carbonated drinks are known culprits. For example, lactose intolerance that might not have been present earlier in life but may be an issue now.

For those in whom gas, bloating or diarrhea are the main symptoms, a low-FODMAP diet may help. FODMAPs (fermentable oligo-, di-, and monosaccharides and polyols) are foods that increase gas production. They include beans, onions, celery, carrots, raisins, bananas, apricots, prunes, Brussels sprouts, wheat germ, pretzels and bagels.

Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit www.health.harvard.edu.

©2024 Harvard University. For terms of use, please see https://www.health.harvard.edu/terms-of-use. Distributed by Tribune Content Agency, LLC.

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