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 medi-cal work-up reveals no apparent explanation for their repeated bouts of abdominal pain, bloating, diarrhoea or constipation.

In fact, irritable bowel syndrome, or I.B.S., is a real problem causing real symptoms, no matter how hard its sufferers may wish it gone. But unlike an infection or tumour, I.B.S. 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.

However, as medical science progresses, experts are beginning to find physical explanations for disorders that previously had no known biological cause. And recent research has revealed at least one likely explanation for the symptoms: an infection in the digestive tract that triggers a localised allergic reaction in the gut.

As Dr Marc E. Rothenberg wrote in The New England Journal of Medicine in June, “Patients with I.B.S. often report that their symptoms started at the time of a gastrointestinal infection.”

Dr Rothenberg, director of the division of allergy and immunology at Cincinnati Children’s Hospital Medical Center, US, 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 I.B.S., including diarrhoea and abdominal pain.

The researchers then showed that a similar immune response occurred in 12 patients with I.B.S. when common food allergens like gluten, wheat, soy or milk were injected into the rectum. Every patient with I.B.S. had a localised reaction to one or more of the allergens, but only two of eight people without I.B.S. 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 I.B.S. 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 I.B.S. may one day find lasting relief.

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 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 it?

It 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 diarrhoea or constipation or both. The disorder affects more women than men and is common in people under 50. 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 I.B.S. Cognitive behavioural therapy may benefit some, 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 I.B.S. and improve patients’ quality of life.

What foods to avoid?

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 to spicy or fatty foods, coffee or alcohol.

NYTNS