Will DisSolving Fiber Solve the IBS Problem?
Abstract & Commentary
By Bridget S. Bongaard, MD, FACP. Dr. Bongaard is the Director of the Integrative Medicine Service Line at CMC-NorthEast Medical Center; she reports no financial relationship to this field of study.
Synopsis: Irritable bowel syndrome symptoms can be treated effectively with soluble fiber such as Metamucil®. The addition of insoluble fiber (such as bran) to the treatment regimen does not confer the same advantage and actually can increase or worsen the symptoms of abdominal bloating and pain. Adding to the utility of this study was that it focused on primary care patients, whereas the comparative reference literature largely addresses patients undergoing care from specialists (secondary care), inferring a more selected population of IBS patients.
Source: Bijkerk CJ, et al. Soluble or insoluble fibre in irritable bowel syndrome in primary care? Randomised placebo controlled trial. BMJ 2009;339:b3154.
Irritable bowel syndrome (IBS) is an extremely common problem for patients presenting to their primary care physician. A large number of these patients are secondarily referred to a gastroenterologist, as the first-line treatment options do not confer a high rate of symptom resolution despite following the international protocols for use of dietary fiber supplementation and antispasmodic agents.
The authors utilized a double-blind randomized control protocol with three arms: Metamucil (psyllium) soluble fiber, bran insoluble fiber, and placebo/control group ingesting rice flour in a cohort of 296 primary care patients with IBS. The groups were analyzed during a 12-week trial that added 10 g of fiber to the average Dutch dietary fiber intake, estimated to be 24 g/d. The patient population included adults age 18-65 years of age with a diagnosis of IBS made in the previous 2 years; however, the exclusion criteria were not stated so it is unknown if the patients had been naïve to fiber treatment at the time of the inclusion, or if other disease processes had been eliminated prior to enrollment. Patients, doctors, and research personnel were blinded to the study protocol, but the practice nurse was aware of treatment rendered. Interestingly, 75% of the patients finishing the study were able to correctly guess which treatment they received when polled in the post-study analysis.
"Adequate symptom relief" of pain and bloating was evaluated as the primary outcome measure at each monthly analysis during the 3-month time period. Secondary outcomes measured at the same time points included: 1) severity of symptoms, 2) severity of abdominal pain, and 3) quality of life. Study dropouts were also tracked each month and categorized for the treatment group as well as the reason for terminating the study. There was a 40% attrition rate over the 12 weeks, with 164 patients equally distributed between the groups (n = 54 psyllium, n = 54 bran, and n = 56 placebo/rice flour) finally finishing the study. The distribution of the 111 patents lost to follow-up was interesting in that 44% were from the bran cohort and 40% from the placebo group, while there was only 36% attrition in the psyllium group. Reasons for discontinuation in the dropout patients ranged from non-medical (n = 15), presumed lack of benefit (n = 10), symptom-free (n = 2), and intolerance of treatment (n = 34). It was notable that the majority of those reporting treatment intolerance were patents ingesting the bran, not the psyllium or placebo.
Primary outcome measures (the rate of response and adequacy of symptom relief) began to differentiate between the three arms even in the first month, with continued improvement in the second and third month in the psyllium-treated patients. During the third month, however, there was not a remarkable statistical distinction between the psyllium and the placebo groups. The bran-treated patients actually fared better than those receiving placebo at the end.
Secondary outcome analysis of reduction in the "severity of the symptoms" illustrated the significant therapeutic effect of psyllium, and the lack of therapeutic difference between bran and placebo. There was no change in either of the latter groups in "severity of abdominal pain" or improvement in the quality of life in these IBS patients after 3 months of treatment. This appeared to be a bit confusing, as the authors did not distinguish those symptoms that specifically improved and those that did not. The authors did attend to patient adherence to the regimen, and calculated the total fiber intake for each group throughout the study, noting that intake did not differ in either arm.
Commentary
The strength of the study is illustrated by the attention to detail of method; however, the blinding of the study had definite limitations given that the patients guessed with fair accuracy which treatment they were given. In addition, the study was further hampered by the 40% dropout rate, which limited the power of the study, though it was noted that the majority of dropouts were those consuming bran. The psyllium patients did respond faster to treatment in the first couple of months, but there was a loss of significant distinction at the third month for those who chose to stay in the trial. These patients also did not report an improvement in symptoms or quality of life, leaving us to wonder precisely which symptoms responded adequately to psyllium. The findings may have therapeutic implication and suggest that the first-line fiber treatment offered in the setting of IBS should be psyllium, and not bran; however, one certainly would want to carefully monitor the patient after the initiation of even such a seemingly common and innocuous supplement as there was persistence of symptoms despite treatment. Adjustment may need to be made in the treatment offered depending on the subtype of IBS presentation.
In a meta-analysis by Ford et al that analyzed 12 studies with a total of 591 patients, psyllium retained therapeutic effectiveness over wheat bran or other insoluble fiber compounds.1 In this analysis, the comment was again made that even the successfully treated patients had persistent symptoms. The caution that it was important to distinguish the symptom type (constipation vs. diarrhea vs. mixed type of IBS) prior to initiation of therapy was countered by findings of favorable response in all three groups to psyllium. Insoluble fiber supplements were noted to increase fecal bulk and decrease intestinal transit time with associated potential for enhanced colonic mucosal health. Bran may therefore confer an intestinal health benefit.
More research is needed to further separate which particular fiber supplement would be most beneficial for each IBS group, and the effects of the fiber type on the internal milieu of the colon including the enterocyte, as well as the bacterial flora within the intestine.
Reference
1. Ford AC, et al. Effect of fibre, antispasmodics, and peppermint oil in the treatment of irritable bowel syndrome: Systematic review and meta-analysis. BMJ 2008:337:a2313.
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