Irritable Bowel Syndrome Message Boards | researcher thinks bacteria a factor in IBS

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Source: University Of Southern California

Date: 2004-09-03

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Bacteria May Be The Cause Of Irritable Bowel Syndrome

Researchers have suggested numerous theories to explain IBS, which affects
as many as 36 million Americans. But according to gastrointestinal motility
specialist Henry C. Lin, associate professor of medicine in the Keck School
of Medicine of USC, the idea of a bacterial origin of IBS represents a major
change in thinking.

Writing in the Aug. 18 issue of JAMA, Lin proposed that ordinary bacteria
normally confined to the large intestine may expand into the small
intestine, prompting uncomfortable bloating and gas after meals, a change in
bowel movements as well as an immune response that may account for the
flu-like illness so common in the IBS patient, including such debilitating
symptoms as headaches, muscle and joint pains and chronic fatigue.

"IBS has long been a frustrating diagnosis for both patients and their
physicians," Lin said. "The bacterial hypothesis of IBS offers new hope for
suffering patients by providing a new framework for understanding the
symptoms of this disorder, pointing to new strategies for treatment."

Physicians frequently diagnose a patient with IBS when ongoing symptoms -
including diarrhea, constipation, bloating, gas and abdominal pain - are not
explained by medical tests such as gastrointestinal endoscopies.

For more than a dozen years, Lin has searched for a common thread to account
for the symptoms in IBS. Studies indicate 92 percent of IBS patients report
bloating after they eat, a symptom he saw again and again in his patients.

While many physicians believe that IBS-related bloating is perceived and not
real, Lin noted that recent studies of IBS patients show that their abdomens
do become measurably more distended than those of healthy patients.

With the symptom of post-meal bloating in mind, Lin began the quest for the
cause of IBS by considering the problem of increased intestinal gas.

Gas comes about when gut bacteria ferment food in the intestinal tract.
There are plenty of organisms in the gut, where bacteria may number 100
trillion.

Bacteria perform a variety of valuable services in the large intestine,
according to Lin. "But we believe problems may start when bacteria set up
shop in the small intestine where they are normally scarce. Usual medical
tests such as endoscopy cannot detect this problem in most patients," he
said.

However, a breath test can be used to indirectly tell if too many bacteria
are in the small intestine. In this test, the patient ingests a syrup
containing the sugar lactulose. Over the next three hours, the gaseous
products of bacterial fermentation of this sugar may be measured in the
exhaled breath.

In a 2003 paper authored by Lin and his research partner Mark Pimentel of
Cedars-Sinai Medical Center, 84 percent of IBS patients were found to have
abnormal breath test results suggesting small intestinal bacterial
overgrowth.

In this double-blind, placebo-controlled study, patients received either
antibiotic therapy or a sugar pill. Patients whose small intestinal
bacterial overgrowth was eradicated by antibiotics reported a 75 percent
improvement in symptoms.

Small intestinal bacterial overgrowth allows gut bacteria to cross the
mucosal barrier, which is the lining of the gut, and enter the body. This
activates the patient's immune system as evidenced by increased numbers of
inflammatory cells in tissues of IBS patients.

"The immune response to bacterial antigens may then explain the flu-like
symptoms that can greatly diminish the quality of life such as chronic
fatigue and pain," Lin said.

The Jill and Tom Barad Family Fund supports Lin's current bacterial
overgrowth research. His other research projects are supported by the
National Institutes of Health.

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Adopt the pace of nature: her secret is patience. ~ Ralph Waldo Emerson

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