On Nutrition

If you’ve ever had a bout of food poisoning, “traveler’s diarrhea” or the stomach flu, only to have some of the symptoms stick around for the long haul — or crop up a few months after you thought you were better — you may have been baffled, frustrated and concerned. What may not have crossed your mind is that you suddenly developed irritable bowel syndrome.

Irritable bowel syndrome (IBS) is a chronic functional bowel disorder, which means that the problem is in how your bowels (intestines) function, but their structure remains normal. IBS causes abdominal pain with diarrhea, constipation or both, and affects around one in 10 people in the United States. While most people with IBS can’t pinpoint when their symptoms started, some people know exactly when it started — right after they were briefly out of commission with intestinal woes.

This type of IBS has a name: post-infectious IBS. It happens after an episode of what is technically called gastroenteritis, an inflammation of the intestinal lining caused by bacteria, a virus or another pathogen. Research suggests that as many as 30% to 40% of people who suffer from a sudden case of gastroenteritis go on to develop post-infectious IBS.

Many pathogens responsible for gastroenteritis can also cause post-infectious IBS, including norovirus and Giardia, a protozoa often found in contaminated food or water. It may also follow a case of traveler’s diarrhea where the exact culprit is unclear. Post-infectious IBS can persist for several months or even several years after the initial illness, although IBS triggered by norovirus generally goes away much sooner. There can also be a time lag between the initial infection and beginning of IBS symptoms — research suggests the chance of developing post-infectious IBS is high even three years after the initial illness — which makes it difficult to connect the dots.

How does something as common (albeit unpleasant) as food poisoning lead to IBS? The pathogen responsible for your illness can disturb both your gut microbiota and the lining of your intestine, activating the immune system and causing low-grade inflammation. It also increases intestinal motility — which basically means that what you eat and drink passes through you faster. All of this can cause diarrhea and other symptoms to hang around long after the pathogen is gone.

What’s behind your belly troubles? Eating for IBS

The risk of developing post-infectious IBS appears to be higher with severe cases of gastroenteritis, especially if symptoms include prolonged or bloody diarrhea, fever or weight loss, or if treatment with antibiotics was necessary. Experiencing depression, anxiety or stressful life events in the three months before the initial infection may prolong the IBS.

Because there’s no test for IBS, diagnosis starts with assessing current symptoms, and often requires eliminating more serious gastrointestinal diseases, such as inflammatory bowel disease (Crohn’s disease and ulcerative colitis) and celiac disease. The hallmark symptoms of IBS are abdominal pain for at least one day per week, on average, in the past three months, along with at least two of these criteria: a change in stool frequency, a change in stool appearance or pain related to defecation.

Post-infectious IBS will resolve gradually and spontaneously in most people, without treatment, but given that IBS can greatly affect quality of life, treatment is a good idea. IBS can be treated with prescription medication or with diet. The main dietary therapy is restriction of fermentable carbohydrates via a FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) elimination diet, followed by a reintroduction phase to see which FODMAPs are triggering symptoms.