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Diet implicated in irritable bowel syndrome

Studies suggest fructose or fat may be the culprits in the gastrointestinal illness, yet physicians say dietary modifications alone are rarely sufficient to eliminate symptoms.

By Victoria Stagg Elliott, amednews staff. Dec. 1, 2003.

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Fat intake or fructose consumption may play a role in irritable bowel syndrome and other gastrointestinal illnesses, according to two papers presented at the October meeting in Baltimore of the American College of Gastroenterology.

One study by researchers at the University of Iowa, Iowa City, found that patients with IBS who were also intolerant to fructose and who followed a fructose-limited diet had significant improvement in their symptoms, while those who did not change their eating habits continued having problems. Another study, this one from the Mayo Clinic College of Medicine in Rochester, Minn., found that patients with functional gastrointestinal disorders, including IBS, seemed to consume more fat and fewer carbohydrates than others.

Physicians said, however, that these studies were not conclusive enough to start restricting the diets of every patient with IBS or other form of gastrointestinal distress and that, in their experience, dietary interventions have mixed results.

"If you take a history, and patients seem to have some connection between certain types of foods such as fresh fruits and vegetables for fructose or milk products for lactose, then you can do a dietary trial, and it can sometimes make a difference," said Keith Holten, MD, associate professor of clinical family practice at the University of Cincinnati College of Medicine. "But just doing dietary maneuvers alone really hasn't been shown to be that effective for large groups of IBS patients."

Not an easy answer

Patients also are not always so eager to make dietary changes.

In the University of Iowa study, half the patients who were deemed fructose intolerant did not alter their eating habits. Researchers suspect the reason might have been because the diet was worse than the disease.

"It's not an easy diet," said Satish Rao, MD, PhD, an author of the paper on fructose and director of neurogastroenterology at the University of Iowa College of Medicine. "And some couldn't be bothered."

Physicians say they sometimes have more success with prescription drugs or psychosocial strategies to help their patients reduce stress or learn to live with the symptoms.

"Dietary intolerances are not more common in people with irritable bowel syndrome than they are in the general population," said Michael Jones, MD, associate professor of medicine in the division of gastroenterology at Northwestern University School of Medicine in Chicago. "It's just that folks with IBS tend to either become more symptomatic or are less tolerant of the symptoms or are more concerned by the symptoms."

Doctors also say that it is not always that easy to determine the root dietary cause of a patient's IBS -- if there is one. Physicians rarely have the time to go through and analyze extensive diet-and-symptoms diaries with patients, and testing is not always easily accessible. The University of Iowa study used a breath test that can be time-consuming and is not widely available.

"I can't tell you the last time I saw the results of a fructose and lactose breath test, much less ordered one," said Dr. Holten. "They're just not commonly done in the primary care setting."

There is also the question of whether dietary information can be clinically as well as statistically relevant. In the Mayo Clinic study, researchers did find a statistically significant difference in fat consumption, but the difference was small, and experts say that the diets of the two groups are actually very similar.

"This study suggests that the dietary issues don't play a major role in these disorders, but they may play some," said G. Richard Locke III, MD, an author on the paper about fat intake and a Mayo associate professor of gastroenterology.

But, more importantly than directing IBS treatment, these studies likely add to the fragmentation of the IBS diagnosis, which many complain is not specific enough to indicate the needed treatment.

It often even falls short of providing patients enough information to manage their symptoms.

"These studies reflect our lack of knowledge about irritable bowel syndrome. We've just kind of clumped it all as one disease," said Suzanne Nelson, MD, MPH, pediatric gastroenterologist at Children's Memorial Hospital in Chicago.

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