Evidence from nine RCTs suggests that fibre is more effective than placebo at improving global symptoms of irritable bowel syndrome (IBS). Subgroup analysis suggests that soluble fibre is more effective than insoluble fibre. Evidence from several small RCTs suggests that fibre does not improve pain or bowel habit compared with placebo. Evidence from one RCT in 80 people suggests that fibre increases bloating compared with placebo. Evidence from two RCTs suggests that soluble fibre is more effective than insoluble fibre at improving global symptoms of IBS.

The Guideline Development Group (GDG) undertook a review of studies of fibre for the management of people with IBS (search date: June 2007) [National Collaborating Centre for Nursing and Supportive Care, 2008]. The GDG identified 20 RCTs for inclusion in the review. Fifteen of the studies included fewer than 100 people, and the majority were undertaken in secondary care.

Fibre compared with placebo (11 studies)

• Global symptoms:
• Improvement in global symptoms (nine studies, n = 545):
• Significantly more people reported an improvement in global symptoms with fibre than with placebo (64% vs. 54%; relative risk [RR] 1.18, 95% CI 1.03 to 1.35).
• Subgroup analysis for soluble and insoluble fibres suggested that soluble fibre was more effective than insoluble fibre.
• Individual symptoms — pain:
• Two single studies (n = 80 in each study) investigated the number of people with less pain or no pain. The confidence intervals were too wide to draw any conclusions.
• Three further studies recorded pain scores. There was little difference between fibre and placebo when the results of these studies were combined.
• Individual symptoms — bloating:
• One study (n = 80) investigated bloating and reported that significantly more people experienced bloating when they took fibre than when they took placebo.
• Individual symptoms — bowel habits:
• Two studies, (n = 106) investigated the number of people with improved bowel habits. When data from the two studies were pooled, there was no significant difference between fibre and placebo in the number of people with improved bowel habits (30% vs. 23%; RR 1.27, 95% CI 0.66 to 2.46).

Insoluble fibre compared with soluble fibre (two studies, n = 281)

• Global outcomes:
• When data from the two studies were pooled, significantly fewer people given insoluble fibre reported an improvement in global symptoms compared with those given soluble fibre (50% vs. 81%; RR 0.61, 95% CI 0.51 to 0.73).
• Individual symptoms — pain:
• Data from one study (n = 185) showed little difference between soluble and insoluble fibre in the number of people with pain.
• Individual symptoms — bowel habits:
• When data from the two studies were pooled, there was no significant difference between soluble and insoluble fibre in the number of people with improved bowel habits.