Ask a Doctor: Why do I have irritable bowel syndrome?


Q: Why do I have irritable bowel syndrome?

A: People with irritable bowel syndrome, or IBS, suffer from recurrent abdominal pain related to having bowel movements – whether it’s diarrhea, constipation or both.

There’s probably no single reason a person may develop IBS, which affects about 15 percent of the U.S. adult population. Instead, different triggers in different people can cause issues along the brain-gut connection. When smooth communication between the brain and gut deteriorates, it changes how people’s bowels move, as well as how they perceive and process pain – ultimately leading to the constellation of symptoms we call IBS.

Here are a few reasons you might have IBS.

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We carry trillions of microbes in our guts, known as the microbiome, that influence our health. One of the most important influencers of our microbiome is our diet, and many people with IBS find their symptoms worsen after ingesting certain foods such as dairy or some fruits.

In IBS, people tend to lose some of the beneficial bacteria such as Lactobacillus and, in turn, gain some of the problematic ones. Studies have shown that making dietary changes to avoid trigger foods can improve IBS symptoms as well as alter the microbiome.

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The strongest-known risk factor for IBS is gastroenteritis, or an acute infection of the gut that results in a few days of bad diarrhea and vomiting. Studies have found that the infection can cause long-term inflammation in the gut, leading to IBS. That damage remains well after the virus or bacteria has left the system.

Gastroenterologists are also investigating whether covid-19 is linked to IBS. In one study, roughly half of covid patients initially reported gastrointestinal symptoms such as diarrhea, vomiting and abdominal pain. A year after getting covid, people have higher rates of IBS than those who didn’t get covid.

As the pandemic evolved, there were several factors at play besides the virus in possibly triggering IBS: the psychological stress of illness (and living through a pandemic), and the various medications, including steroids, often used during treatment that may have impacted the microbiome.

IBS is often a lifelong condition. But with IBS that develops after an acute infection, most people can expect a gradual recovery after months or years.

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Major life stressors go hand-in-hand with IBS-symptom intensity, and people who have experienced traumatic life events have a higher risk of developing IBS.

Famous studies conducted on rats have shown that being separated from a mother in infancy as well as experiencing irritation in the colon shortly after birth can lead to changes in the neurons that control pain perception in the gut as adults.

Emotional, physical or sexual trauma early in life can predict the development of IBS, especially for women. Traumatic events in adulthood also increase your risk.

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Studies have shown that if you have a close relative with IBS, such as a sibling or a parent, then you have an increased chance of having IBS yourself. There’s also genetic data supporting the idea that IBS is, in part, sex related: Women tend to be more affected than men.

But genetic research has just started to unpeel the mystery of which genes may play key roles in why IBS happens. Several studies have implicated tiny variations in the genes responsible for serotonin and its signaling pathways. The overwhelming majority of the body’s serotonin, sometimes dubbed the “feel-good” hormone, is actually found in the gut, where it helps regulate bowel movements, secretions and sensations.

Other large studies have revealed that mood disorders share a genetic origin with IBS – and may be why medications that are commonly thought of as anti-depressants or anti-anxiety also help IBS symptoms.

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The gravity hypothesis

A recent hypothesis proposed by gastroenterologist Brennan Spiegel at Cedars-Sinai Medical Center in Los Angeles suggests that gravity – or rather, our bodies’ inability to manage it – could be the unifying problem behind IBS. The idea is that Homo sapiens evolved to compensate for the gravitational force around us.

Our guts, for instance, are not haphazardly clumped at the bottom of our bellies in a big pile. Instead, our bodies have a system of connective tissue tethers that holds them up in an array against gravity, allowing for the smooth passage and processing of nutrients.

But for some people, according to Spiegel, those suspension systems are more susceptible to becoming overstretched. When that happens, in theory, kinks occur that block the flow of stool, and it can cause bacterial overgrowth and a heightened sensitivity of the nerves in the gut. It’s perhaps part of why interventions that strengthen our body’s natural anchors – such as yoga and other forms of exercise – are beneficial in treating IBS.

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There is no single cure for IBS. Discussing possible triggers can sometimes help your doctor treat your condition, whether it’s with medication, brain-gut psychotherapy or changes to your diet.

As a gastroenterologist, I know how reluctant people can be to discuss their poop with a stranger. But believe me, we’ve heard it all. And while the reason you have IBS may be outside your control, taking the first steps to get the help you need is.

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Dr. Trisha Pasricha. PHOTO:

Trisha S. Pasricha is a gastroenterologist at the Massachusetts General Hospital Center for Neurointestinal Health and a medical journalist.



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