Soluble or insoluble fibre in irritable bowel syndrome in primary care? Randomised placebo controlled trial

Editor;

The role of fibre in the treatment of irritable bowel syndrome
remains controversial. For this reason, Bijkerk and colleagues are to be
applauded for conducting the most rigorous randomised controlled trial
(RCT) of soluble and insoluble fibre supplementation in IBS yet published,
and the first to be conducted entirely in primary care. 1

A recent systematic review and meta-analysis that examined the
efficacy of fibre in IBS reported a beneficial effect of soluble fibre in
the form of psyllium (or ispaghula husk) in IBS, 2 with a number needed to
treat (NNT) of 6 (95% CI 3 to 50), but acknowledged that many studies were
small, of poor quality, open to potential bias, and of questionable
relevance to primary care as all were conducted in the specialist setting.
Insoluble fibre, in the form of bran, was of no benefit in IBS, though it
was not possible to examine any potentially deleterious effect on symptoms
that have been proposed by some investigators, 3 due to the manner in
which data were reported in the eligible RCTs. In Bijkerk and colleagues’
trial the high drop-out rates at 12 weeks meant that the effect of
ispaghula on abdominal pain or discomfort were only modest, with 29% of
patients responding to therapy in their worst case analysis, but if these
data are incorporated into the aforementioned meta-analysis the NNT
remains reassuringly similar at 7 (95% CI 4 to 25).

What is puzzling to us is that Bijkerk and colleagues report in their
discussion that “bran showed no clinically relevant benefit, and many
patients seemed not to tolerate bran”. Whilst there were more trial
patients who did not tolerate bran, this numerical difference did not
reach formal statistical significance and, in those who were able to
continue therapy, its effect on abdominal pain and discomfort after 12
weeks was superior to both ispaghula and placebo, in both the intention to
treat and worst case analysis, and IBS symptom severity scores improved
compared with placebo.

It would appear then, from this trial, that there are certain
patients with IBS in primary care whose symptoms actually respond to
insoluble fibre supplementation, and therefore its utility as a
therapeutic strategy should not be so easily disregarded, and further
studies as to which subgroup of IBS patients (if any) may benefit from
this intervention are warranted.

Alexander C Ford1

Paul Moayyedi2

1Lecturer in Medicine, Department of Academic Medicine, St. James’s
University Hospital, Beckett Street, Leeds, LS9 7TF, UK.

2Professor of Gastroenterology, Gastroenterology Division, McMaster
University, Health Sciences Centre, Hamilton, Ontario, L8N 3Z5, Canada.

REFERENCES

1. Bijkerk CJ, de Wit NJ, Muris JWM, Whorwell PJ, Knotterus JA, Hoes
AW. Soluble or insoluble fibre in irritable bowel syndrome in primary
care? Randomised placebo controlled trial. Br Med J 2009;339:b3154.
doi:10.1136/bmj.b1354

2. Ford AC, Talley NJ, Spiegel BMR, Foxx-Orenstein AE, Schiller L,
Quigley EMM, Moayyedi P. Effect of fibre, antispasmodics and peppermint
oil in the treatment of irritable bowel syndrome: systematic review of the
literature and meta-analysis. Br Med J 2008;337;a2313.

3. Francis CY, Whorwell PJ. Bran and irritable bowel syndrome: time
for reappraisal. Lancet 1994;344:39-40.

Competing interests:
None declared