A few years ago, a 45-year-old schoolteacher with irritable bowel syndrome, whom I had treated with limited success for several years, called me, her voice filled with excitement. A friend in a local IBS support group had been put on a special diet and was feeling like a new person.

When my patient initially came to see me, she had all of the symptoms of IBS, the most commonly diagnosed gastro­intestinal disorder in the U.S. Over the previous few months, she had experienced intermittent bouts of severe abdominal pain with diarrhea that lasted several days, which alternated with episodes of constipation, gas, and bloating.

Diagnostic Dilemmas

Her symptoms posed a formidable diagnostic challenge because several other intestinal disorders mimic IBS. She hadn’t lost weight and didn’t have bloody stools, which might have signified a more ominous illness, such as colon cancer or ulcerative colitis. All of her routine blood tests were normal. Because she had recently been in India, I had her stools checked for parasites such as giardia, which can cause long-lasting symptoms. No such parasites were found.

Tests for celiac disease were also negative. To rule out nonceliac gluten sensitivity, the teacher tried a one-month gluten-free diet which brought no benefit. Her colonoscopy was normal. We were both hopeful when she improved on a lactose-free diet, only to see her symptoms return after a few weeks.

Because I was unable to pinpoint a disease to account for her symptoms, I was left, by exclusion, with a diagnosis of IBS, a disorder without a clear cause or good treatment. Despite decades of intense study, no biochemical or pathological marker for IBS has been found.

But two typical abnormalities have emerged. One is a heightened sensitivity to normal amounts of intestinal gas. The second is poorly coordinated contractions of the intestinal muscle that normally help propel stool to its ultimate destination. When that occurs too rapidly, people have diarrhea; too slowly, constipation.

Man clutching his stomach, in discomfort.

Treating a Moving Target

Over the years, my patient was able to find a measure of relief by avoiding foods that seemed to act as triggers for her symptoms: alco­hol, caffeine, apricots, bananas, beans, brussels sprouts, onions, prunes, and raisins. Because of her brief beneficial experience with lac­tose avoidance, she also continued to steer clear of dairy foods.

I also advised limited use of medications and focused on whichever phase of IBS she was in at the time. During per­i­ods of constipation, for ex­ample, she typically used over-the-counter pol­yethylene glycol (Mir­alax and generic). Then, when the diarrheal phase began, I found the best remedy to be OTC loperamide (Imodium A-D and generic).

Several prescription medications—including anti-­spasmodics such as hyoscyamine and older anti­depressants such as amitriptyline (Elavil and generic) and desipramine (Norpramin and generic)—may also improve symptoms, the latter especially where depression may play a role. And probiotics to alter the mix of good-to-bad gut bacteria have yielded promising results in limited trials. But no medication works well all of the time.

A Newer, Better Diet?

So when my patient called about her friend’s special diet, it came as no surprise to me. Studies show that those with IBS consider food to be the most common trigger. And self-directed dietary changes have resulted in anecdotal improvement in many people.

What the teacher’s well-meaning friend was referring to was the increasingly popular low-FODMAP diet. (FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols—all carbohydrates.) In addition to the usual gas-producers, items to avoid include wheat-containing products and those with fructose, such as apples, cherries, mangoes, and pears. Several randomized, albeit small, controlled studies have shown significant improvement for IBS patients on low-FODMAP diets.

I referred my patient to a registered dietitian for formal instruction about the diet, which she eagerly adopted. Now, although she still has occasional breakthrough bouts of diarrhea, overall she is a much happier person than she was prior to that phone call from a friend.