IBS in the crosshairs

Up to 45 million Americans have a condition that people affected may only reluctantly mention: irritable bowel syndrome, or IBS. Despite its prevalence, IBS is still somewhat mysterious when it comes to who gets it — two-thirds of patients are women — and why.

But scientists are steadily peeling this proverbial onion, with newer treatment approaches targeting pathways that appear to be involved in the cramping, bloating, gas, diarrhea, and/or constipation that disrupt patients' everyday lives.

Marked by chronic belly pain and altered bowel habits, IBS is categorized into three types according to which symptoms dominate: diarrhea (IBS-D), constipation (IBS-C), or a combination. It's one of the most common gastrointestinal conditions, affecting up to 15% of Americans, according to the International Foundation for Gastrointestinal Disorders.

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. But that label is problematic, Harvard experts say.

"To say nothing's wrong is just wrong, because clearly something is different," says Dr. Anthony Lembo, a gastroenterologist at Harvard-affiliated Beth Israel Deaconess Medical Center. "It's just that our standard clinical testing can't show it."

Compelling effects on daily life

The causes of IBS remain frustratingly unclear, but symptoms are believed to stem from any of a wide range of factors. Among them:

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 — show a higher rate of IBS," Dr. Lembo says.

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.

At best, 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.

"All the data show the suffering is pretty significant," Dr. Lembo says. "It's a disorder we know can really debilitate people."

Tailoring treatments

For the first time, IBS treatment guidelines, updated in June 2022 by the American Gastroenterological Association, steer doctors on how to personalize patients' treatment with a widening assortment of medications.

Over-the-counter options — including fiber supplements, laxatives (in limited amounts), and anti-diarrheals — can help control symptoms. But recent years have brought an influx of IBS-specific drug options that don't just address symptoms, but instead target specific biochemical or cellular pathways to slow food movement through the bowel or push fluids into the intestine to soften stools and speed their passage. For IBS-D, these drugs include alosetron (Lotronex) and eluxadoline (Viberzi). For IBS-C, they include lubiprostone (Amitiza), linaclotide (Linzess), plecanatide (Trulance), and tenapanor (Ibsrela).

The antibiotic rifaximin (Xifaxan) appears to benefit the gut microbiome, suppressing "bad" organisms that contribute to IBS symptoms, says Dr. Lawrence Friedman, assistant chief of medicine at Harvard-affiliated Massachusetts General Hospital and chair of the Department of Medicine at Newton-Wellesley Hospital. "It's one of the more exciting newer developments," he says.

Doctors are also tapping older drugs for new purposes. Various antidepressants can alter nerve signal activity in the intestines or lessen pain in IBS, Dr. Lembo says.

While a variety of medications can help relieve symptoms, effective IBS management depends on 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. Meanwhile, peppermint oil supplements, taken as coated tablets, can ease bloating and pain.

"Many people also figure out that lactose can be a trigger and if they drink a glass of milk or consume other dairy products, their symptoms worsen," Dr. Lembo says. "But sometimes it's more subtle than that. Even drinking a glass of diet soda can cause gas and bloating."

For those in whom gas and bloating are severe, 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. Dr. Lembo suggests eliminating FODMAPs temporarily and then slowly adding each food back into your diet to pinpoint the worst offenders.

Over all, Dr. Friedman says, "the spectrum of treatments has expanded. We have more tools to work with and there's a higher likelihood of success, but there may still be an element of trial and error involved."

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