Aug. 28, 2009 -- Psyllium, the soluble fiber in Metamucil and other products, can relieve abdominal pain and discomfort in some patients with irritable bowel syndrome (IBS).

Bran, an insoluble fiber, did not help most patients and worsened symptoms in many, according to the results of a 275-patient clinical trial.

"The results of this large-scale trial ... support the addition of soluble fiber, such as psyllium, but not bran as an effective first treatment approach in the clinical management of patients with irritable bowel syndrome," conclude C.J. Bijkerk, MD, of University Medical Center, Utrecht, Netherlands, and colleagues.

Study participants were randomly allocated to three groups. One group received two 10-gram doses of psyllium a day, usually to be mixed with yogurt. A second group received similar doses of bran, and a third group received a non-fiber placebo (rice flour) to mix with their yogurt.

About 40% of the participants dropped out of the study; the dropout rate was highest among those taking bran. Despite the blinded nature of the study, about three-fourths of the patients figured out what it was they were getting.

After each month of the three-month study, patients were asked, "Did you have adequate relief of irritable bowel syndrome-related abdominal pain or discomfort in the past week?"

Patients receiving psyllium were more likely to say "yes" during the first two months of the study. Those with constipation-predominant IBS were only slightly more likely to report relief than were patients with diarrhea-predominant or mixed-type IBS.

Those who received psyllium were also more likely to report significant reduction in the severity of their symptoms.

"After three months of treatment, symptom severity in the psyllium group was reduced by 90 points, compared with 49 points in the placebo group and 58 points in the bran group," Bijkerk and colleagues report.

The study appears in the Aug. 28 Online First issue of BMJ.