Health

What causes IBS? Experts are beginning to untangle this perplexing condition

What researchers are discovering about irritable bowel syndrome could offer clues for treating it

IBS is the most frequently diagnosed gastrointestinal disorder. Illustration: Gracia Lam/The New York Times

Jane E Brody
Fri Aug 6 2021 - 06:00

No one with debilitating symptoms likes to be told “it’s all in your head.” Yet, this is often what distressed patients with irritable bowel syndrome hear, implicitly or explicitly, when a medical work-up reveals no apparent explanation for their repeated bouts of abdominal pain, bloating, diarrhea or constipation.

In fact, irritable bowel syndrome, or IBS, is a real problem causing real symptoms, no matter how hard its sufferers may wish it gone. But unlike an infection or tumor, IBS is what medicine calls a functional disorder: a condition with no identifiable cause.

Patients have no visible signs of damage or disease in their digestive tracts. Rather, the prevailing theory holds that overly sensitive nerves in the patient’s gastrointestinal tract send distress signals to the brain that result in pain and malfunction.

Common gastrointestinal ailments, such as IBS and functional abdominal pain, may actually be food-induced allergic disorders

However, as medical science progresses, experts are beginning to find physical explanations for disorders that previously had no known biological cause. For example, conditions like epilepsy, Alzheimer’s disease and migraine were once considered functional disorders, but are now known to have measurable physical or biochemical underpinnings.

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And recent research has revealed at least one likely explanation for the symptoms of IBS: an infection in the digestive tract that triggers a localized allergic reaction in the gut. As Dr Marc E Rothenberg wrote in The New England Journal of Medicine in June, “Patients with IBS often report that their symptoms started at the time of a gastrointestinal infection.”

Dr Rothenberg, who is the director of the division of allergy and immunology at Cincinnati Children’s Hospital Medical Center, explained in an interview that the infection can temporarily disrupt the layer of cells that normally lines the bowel. These cells form a barrier that prevents allergy-inducing proteins in foods from being absorbed. When that barrier is penetrated, people can become intolerant to foods that previously caused them no issue.

A study in mice published in the journal Nature in January showed how this might happen. After infecting the rodents’ guts with bacteria, researchers found that the microbes released toxins that initiated an allergic reaction in the intestines, sparking the immune system to create antibodies against specific dietary proteins. When those specific proteins were ingested from foods, an immune reaction caused the rodents’ stomach muscles to contract, mimicking the symptoms of IBS, including diarrhea and abdominal pain.

The emotional distress IBS can cause often results in depression and anxiety and may prompt others to think incorrectly that the bowel disorder is self-inflicted

The researchers then showed that a similar immune response occurred in 12 patients with IBS when common food allergens like gluten, wheat, soy or milk were injected into the rectum. Every patient with IBS had a localised reaction to one or more of the allergens, but only two of eight people without IBS reacted to any allergen. Unlike classic food allergies that can produce hives, swelling and other body-wide immune responses, the reaction to allergens in the study was detectable only in the colon.

In describing this intriguing research, Dr Rothenberg noted that “a great deal remains to be elucidated.” But he added that this and other related research suggests that “common gastrointestinal ailments, such as IBS and functional abdominal pain, may instead be food-induced allergic disorders”.

Such findings, the researchers wrote in the January study, hint at “new possibilities for the treatment of irritable bowel syndrome and related abdominal pain disorders,” offering hope that people with IBS may one day find lasting relief.

Such remedies would be a godsend for the 10 to15 percent of adults in the United States with IBS or other food sensitivities who experience gastrointestinal distress following a meal.

Therapeutic possibilities include high doses of antihistamines to counter patients’ sensitivities, as well as targeted treatments that block allergic pathways, Dr Rothenberg said. He added that there are now drugs in Phase 3 trials – the step before approval – that eliminate the immune cells, known as mast cells, that are responsible for initiating an allergic response in the gut.

How common is IBS?

IBS is the most frequently diagnosed gastrointestinal disorder. Although symptoms can vary from patient to patient, they commonly include cramping, abdominal pain, bloating, intestinal gas, and diarrhea or constipation, or both. The disorder affects more women than men and is most common in people under 50. The annual medical costs of the condition exceed $1 billion (€843 million) in the United States alone.

It’s a chronic condition that requires continual management strategies, like always knowing the location of the nearest bathroom or having to wear diapers when restroom access is limited. The emotional distress it can cause often results in depression and anxiety and may prompt others to think incorrectly that the bowel disorder is self-inflicted.

Can calming therapies help?

There is a known connection between the brain and the gut, and undue stress can certainly aggravate the symptoms of IBS. Cognitive behavioral therapy may benefit some patients, and many find it helpful to practice relaxation techniques like positive imagery, progressive muscle relaxation or meditation.

Yoga and other types of physical activity may also diminish symptoms of IBS and improve patients’ quality of life. One clinical trial involving 102 patients found that those who engaged in vigorous physical activity three to five days a week experienced reduced physical and psychological symptoms.

Another soothing technique that can be done anywhere, anytime, to help relieve pain and stress is diaphragmatic breathing, the opposite of sucking in your gut. Instead of pushing out the chest as the lungs fill with air, the diaphragm is pushed down toward the stomach, causing the belly to rise. Practice by placing one hand above your navel to feel your abdomen rise as you inhale slowly through your nose, and then retract as you exhale through your mouth.

Which foods should be avoided if i have

IBS?

Patients can also minimise their symptoms by avoiding the foods or drinks that seem to trigger them. Common troublemakers include wheat and other gluten-containing foods, dairy products, citrus fruits, beans, cabbage and related gas-causing vegetables, and carbonated drinks. People may also react badly to spicy or fatty foods, coffee or alcohol.

Some patients find dramatic relief from adopting a strict FODMAP diet that eliminates all fermentable starches and sugars, then gradually adding back one food at a time to determine which ones cause symptoms and are best avoided. The FODMAP diet favorably alters the population of microbes that live in the intestines, reducing gas-producing bacteria that thrive on fermentable foods. Details of the diet can be found at this website.

Some evidence suggests that prebiotics or probiotics may be another therapeutic option to manipulate the bacteria that dwell in the intestinal tract, though the findings are limited. In a recent review in JAMA Network, Dr Michael Camilleri, a gastroenterologist at the Mayo Clinic, reported that the probiotic Bifidobacterium longum reduced depression and improved quality of life for patients with IBS.