Irritable Bowel Syndrome Message Boards | Systematic Review: The Role of Different Types of Fibre in IBS

Systematic Review: The Role of Different Types of Fibre in IBS

This systematic review shows that there is limited and conflicting evidence for the effectiveness of fibre in the treatment of irritable bowel syndrome symptoms. For the measure of efficacy, i.e. the proportion of patients with global irritable bowel syndrome symptom improvement, fibre was significantly better than control. Fibre therapy also showed favourable results in irritable bowel syndrome-related constipation. However, it may increase abdominal pain in some irritable bowel syndrome patients. The effect of psyllium on constipation was based on only two studies: Jalihal and Kurian[25] with a dose of 30 g and Prior and Whorwell[28] with a dose of approximately 5 g. Pooling with other studies with a lower dosage might underestimate the effects of a reasonable dose of psyllium.

The two types of fibre, soluble and insoluble, affected irritable bowel syndrome symptoms differently. Soluble fibre was beneficial to global symptom improvement, whereas insoluble fibre was not more effective than placebo and may, in some irritable bowel syndrome patients, worsen symptoms when compared with a normal diet. In two studies, a considerable effect was found. In one of these, a reasonable dose of psyllium was used.[25] Toskes et al. used calcium polycarbophil, which is a synthetic fibre resistant to bacterial degradation.[29] Pooling of these studies with other psyllium studies that use sub-optimal doses underestimates the treatment effect.

Evidence for the effectiveness of soluble fibre was obtained from the pooled results. Irritable bowel syndrome patients treated with this type of fibre reported 1.3 times more global improvement than controls. The effect of soluble fibre on irritable bowel syndrome-related abdominal pain, however, was controversial. Indeed, the studies that reported on the outcome measure of relief of abdominal pain varied considerably and showed conflicting results.[24,25,28]

The efficacy of insoluble fibre in the treatment of irritable bowel syndrome patients was also controversial. The studies showed that diets with a large amount of insoluble fibre might actually be worse than a normal diet. The clinical improvement of irritable bowel syndrome patients treated with insoluble fibre was no better than that obtained with placebo.[33,34,37,38]

The outcomes used in each of the randomized trials varied considerably. Consequently, several important outcomes were reported in only some of the trials. Moreover, they were measured in different ways. Generic outcomes, such as the quality of life, were not used in any of the trials. In terms of both global irritable bowel syndrome symptom improvement and individual symptom improvement, the studies showed heterogeneous results. The main reason for this may be the small sample sizes studied, which could have produced type II errors. Two studies in our analysis used either a single-blind or an open allocation of intervention,[36,39] whereas it is recommended that double-blind assessment should be used in irritable bowel syndrome trials.[40] However, many difficulties are encountered in the design and execution of trials with dietary intervention. As blinding is difficult in trials evaluating high-fibre dietary advice, we accepted these studies.

Three studies were excluded from our analysis as no data could be extracted to calculate a relative risk. None of these showed a positive response to treatment. This might have given rise to an over-estimation of the effectiveness of fibre.

The majority of patients with irritable bowel syndrome are managed in primary care.[4] Unfortunately, none of the selected studies included patients treated in a primary care setting. This limits the external validity of our results. Irritable bowel syndrome patients in primary care may, in fact, respond differently to dietary therapy than referred patients.[41] Furthermore, primary care patients who respond to treatment with bulking agents are less likely to be referred to a hospital clinic. Moreover, more than half of the symptomatic 'patients' from the general population do not even present to their general practitioner. The efficacy of fibre in this population is unknown.

The role of fibre in the pathophysiology of irritable bowel syndrome remains poorly understood.[42] An increase in the amount of dietary fibre is an almost universal recommendation in the primary care management of irritable bowel syndrome,[3,5] and guidelines on irritable bowel syndrome management for out-clinic patients advise an increase in fibre intake in the event of constipation.[5,43] However, our review showed only limited support for this recommendation.

In summary, our systematic review demonstrates the effectiveness of fibre therapy in irritable bowel syndrome patients, but only in terms of either global symptom improvement or constipation. The effectiveness on individual symptoms is variable. There is no effect of fibre in irritable bowel syndrome-related abdominal pain. Soluble and insoluble fibre have different effects on global irritable bowel syndrome symptoms. Insoluble fibre is probably no better than placebo and may, in some patients, even worsen the clinical outcome. For the development of evidence-based management guidelines, valid clinical studies in primary care patients, focusing on the effectiveness and tolerability of soluble and insoluble fibre, are needed.

Dr J.W.M. Muris, Maastricht University, Department of General Practice, PO Box 616, NL-6200 MD Maastricht, The Netherlands. E-mail: jean.muris@hag.unimaas.nl

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Aliment Pharmacol Ther 19(3):245-251, 2004. � 2004 Blackwell Publishing

http://www.medscape.com/viewarticle/469549_4

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