Soluble or insoluble fibre in irritable bowel syndrome in primary care? Randomised placebo controlled trial
BMJ 2009; 339 doi: https://doi.org/10.1136/bmj.b3154 (Published 27 August 2009) Cite this as: BMJ 2009;339:b3154
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Irritable Bowel Syndrome (IBS) is a common nonspecific diagnosis for functional
lower gastrointestinal symptoms of abdominal pain, bloating, constipation,
diarrhea, and anxiety. In my experience, IBS responds best to regular aerobic
exercise (which facilitates peristalsis), cooked fruits and vegetables (which
facilitates digestion of soluble and insoluble fiber), roasted flax seeds and
sesame seeds (both of which must be chewed well before swallowing), and
discussions that explore the patient’s feelings about defecation and feces. It is
best to try these safe, natural approaches before resorting to drugs, which can
complicate, aggravate, and perpetuate the symptoms.
Competing interests:
None declared
Competing interests: No competing interests
Bijkerk et al examined the effectiveness of increasing the dietary
content of soluble fibre (psyllium) or insoluble fibre (bran) in patients
with irritable bowel syndrome (1). Participants were randomised to 12
weeks of treatment with 10g psyllium, 10g bran or 10g placebo (rice
flour). When reading this article, it is not entirely clear how the
randomisation sequence was generated. At first reading it seems that the
randomisation sequence was generated using blocked randomisation with a
block size of 6 and was concealed using sealed non-opaque envelopes. Yet
this would imply that there should only be a difference of, at most, 2
patients between the treatment groups. However, there was a disparity of
12, 8 and 4. Consequently the authors cannot have used fixed block sizes
as suggested in their paper. Can the investigators describe their
randomisation process in more detail in order to explain the unexpected
discrepancy in group sizes?
David J Torgerson, PhD, Director, York Trials Unit
Catherine E Hewitt, PhD, Research Fellow, York Trials Unit
(1) Bijkerk CJ, de Wit NJ, Muris JWM, Whorwell PJ, Knottnerus JA,
Hoes AW. Soluble or insoluble fibre in irritable bowel syndrome in
primary care? Randomised placebo controlled trial. BMJ 2009; 339: b3154
doi:10.1136/bmj.b3154
Competing interests:
None declared
Competing interests: No competing interests
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
Competing interests: No competing interests
Psyllium, stool thickness and potential for bezoar formation.
I have prescribed psyllium on many occasions, exclusively for
decreasing the liquidity in stool and optimizing sphincteric control after
closing the defunctioning ileostomy following a total abdominal colectomy
and ileo-anal anastomosis performed for ulcerative colitis. Taken in
larger amounts it usually acts as a cathartic but has the potential to
cause obstruction by removing fluid from stool and promoting the formation
of a bezoar(1). There are several reversible causes of symptoms
attributable to the "irritable bowel syndrome", including chronic
mesenteric ischaemia(2), and these should be excluded and reversed if
found before resorting to extended empirical therapy including the
administration of supposedly soluable psyllium and/or insoluable bran.
1. Farooq P. Agha, Timothy T. Nostrant, Richard G. Fiddian-Green.
"Giant Colonic Bezoar": A Medication Bezoar Due to Psyllium Seed Husks.
The American Journal of Gastroenterology. Volume 79 Issue 4, Pages 319 -
321
2. Michel Lièvre. Alosetron for irritable bowel syndrome
BMJ 2002; 325: 555-556 [See rapid responses].
Competing interests:
None declared
Competing interests: No competing interests