Soluble Fiber May Be Effective for Symptoms of IBS

From Medscape Medical News CME
Laurie Barclay, MD & Charles P. Vega, MD

BMJ. 2009;339:b3154. Abstract

Clinical Context

IBS has a population-wide prevalence of approximately 10%, according to the authors of the current study. However, only a minority of individuals with IBS seek medical care for their symptoms. Most patients with IBS are women, and, although most cases of IBS are managed in primary care practices, few primary care clinicians use formal criteria to diagnose IBS.

Dietary advice and fiber supplements are considered mainstays of therapy for IBS. The current study compares a soluble fiber (psyllium) and insoluble fiber (bran) vs placebo in the treatment of IBS.


Study Highlights

Study participants included adults between the ages of 18 and 65 years who had been diagnosed with IBS in the previous 2 years. The study was conducted in primary care practices in the Netherlands. Diagnoses of IBS were identified through billing data, and researchers evaluated whether patients met formal diagnostic criteria for IBS as well.
Patients who had received fiber treatment in the past 4 weeks, who had a psychiatric disorder, or who had another diagnosis of organic bowel disease were excluded from study participation.
Participants were randomly assigned to receive 10 g of psyllium, 10 g of bran, or rice flour placebo in 2 daily dosages. Each study treatment was mixed with food, preferably yogurt. The treatment period was 3 months.

The main outcome of the study was adequate symptom relief for at least 2 weeks of the previous month, which was defined as response to treatment. Secondary outcomes included a measurement of IBS symptom severity, the severity of abdominal pain specifically, and disease-specific quality of life.
275 patients underwent randomization. 78% of participants were women, and 94% were white. The mean age of participants was 34.4 years.
Only 39% of participants fulfilled the Rome II diagnostic criteria for IBS. Most subjects had constipation-predominant IBS.
The mean intake of daily fiber before study treatment was 26.9 g/day, which was consistent with national average consumption in the Netherlands.

Only 60% of participants attended the final visit at the end of the 3-month study period. Most patients who left the trial did not provide a reason for discontinuing their participation, but study discontinuation was most common among the bran group in the first study month. Most of these patients complained of a worsening of IBS symptoms.
Among patients who remained in the trial, adherence to study therapy was similar in the psyllium and bran groups, as were the consumption of dietary fiber and total fluids.

57% of participants receiving psyllium experienced a treatment response at 1 month vs 35% of participants receiving placebo. The respective response rates at month 2 were 59% and 41%, and psyllium was significantly superior to placebo in both months. The superiority of psyllium was lost in the third month of the trial.
Subgroup analysis focusing on patients who met Rome II criteria for IBS suggested that psyllium may be even more effective for these patients. Psyllium remained more effective than placebo in an analysis limited to participants with constipation-predominant IBS.
Bran was superior to placebo in the main study outcome only in the third month of the trial.
Psyllium was associated with a significant overall reduction in IBS symptoms vs placebo, whereas bran was not.
Neither psyllium nor bran relieved IBS abdominal pain or improved quality of life vs placebo. The percentages of participants who remained in the study and reported adverse events were 74%, 64%, and 66% in the psyllium, bran, and placebo groups, respectively. Diarrhea and constipation were the most commonly reported adverse events and were common in all treatment groups.

Clinical Implications

The prevalence of IBS is approximately 10%, with a predilection for women. Most patients with IBS do not seek medical care for their symptoms, and most primary care physicians do not use formal criteria to diagnose IBS.
The current study suggests that psyllium may relieve IBS symptoms, whereas bran may worsen symptoms.