This uncommissioned systematic review was subject to full peer-review.
Systematic review: the effects of fibre in the management of chronic idiopathic constipation
Article first published online: 20 FEB 2011
© 2011 Blackwell Publishing Ltd
Alimentary Pharmacology & Therapeutics
Volume 33, Issue 8, pages 895–901, April 2011
How to Cite
Suares, N. C. and Ford, A. C. (2011), Systematic review: the effects of fibre in the management of chronic idiopathic constipation. Alimentary Pharmacology & Therapeutics, 33: 895–901. doi: 10.1111/j.1365-2036.2011.04602.x
- Issue published online: 17 MAR 2011
- Article first published online: 20 FEB 2011
- Publication data Submitted 13 January 2011 First decision 27 January 2011 Resubmitted 30 January 2011 Accepted 31 January 2011 EV Pub Online 20 February 2011
Aliment Pharmacol Ther 2011; 33: 895–901
Background Patients with chronic idiopathic constipation are often told to increase dietary fibre intake. Whether this is of any benefit remains unclear.
Aim To conduct a systematic review of the efficacy of soluble and insoluble fibre supplementation in the management of chronic idiopathic constipation.
Methods MEDLINE, EMBASE, and the Cochrane central register of controlled trials were searched to identify randomised controlled trials (RCTs) comparing fibre with placebo or no therapy in adult chronic idiopathic constipation patients. Studies had to report dichotomous data assessing response to therapy, or continuous data examining either effect of therapy on mean number of stools per week, or mean symptom scores. Adverse events data were extracted where reported.
Results Six RCTs were eligible. Four used soluble fibre and two used insoluble fibre. Formal meta-analysis was not undertaken due to concern about methodological quality of identified studies. Compared with placebo, soluble fibre led to improvements in global symptoms (86.5% vs. 47.4%), straining (55.6% vs. 28.6%), pain on defaecation, and stool consistency, an increase in the mean number of stools per week (3.8 stools per week after therapy compared with 2.9 stools per week at baseline), and a reduction in the number of days between stools. Evidence for any benefit of insoluble fibre was conflicting. Adverse events data were limited, with no RCT reporting total numbers.
Conclusions Soluble fibre may be of benefit in chronic idiopathic constipation, but data for insoluble fibre are conflicting. More data from high quality RCTs are required before the true efficacy of either fibre type in the treatment of chronic idiopathic constipation is known.
Chronic idiopathic constipation (CIC) is a common condition affecting the gastrointestinal (GI) tract, with an estimated prevalence of between 4% and 20% in cross-sectional community surveys.1–4 This functional disorder is defined as the infrequent and difficult passage of stools in the absence of any physiological abnormality.5 The condition is commoner in women, the elderly, and those with lower income4, 6, 7 and is associated with reduced quality of life.8
Symptoms of CIC can be difficult to treat.9 Lack of dietary fibre is believed to contribute to constipation,10 and many physicians recommend an increase in fibre intake, along with other lifestyle modifications such as improved hydration, as an initial therapy. Insoluble fibres, such as wheat bran, are thought to exert their effect by accelerating intestinal transit time, thereby increasing stool frequency.11 Psyllium, which is a soluble fibre derived from ground ispaghula husk, is ingested with water to increase stool bulk and increase stool frequency.12
There have been several randomised controlled trials (RCTs) studying the effects of both soluble and insoluble in individuals with CIC published previously, and current guidelines from national and international Gastroenterology organisations advocate the use of dietary fibre as a first-line therapy for constipation.13, 14 Despite this, there has been no recent summary of all available published RCTs to determine what evidence there is, if any, to support the use of fibre in the treatment of CIC. We have therefore conducted a systematic review to examine this issue.
Search strategy and study selection
A search of the medical literature was conducted using MEDLINE (1950 to September 2010), EMBASE and EMBASE Classic (1947 to September 2010), and the Cochrane central register of controlled trials (Issue 3, July 2010) to identify RCTs examining the efficacy of soluble or insoluble fibre in adults (>90% of participants over the age of 16 years) with CIC. The first period of cross-over RCTs were also eligible for inclusion. The presence of CIC could be defined according to clinical symptoms, a physician’s diagnosis, or the Rome I, II, or III criteria,5, 15, 16 with organic causes excluded by negative investigations if trial investigators felt this necessary. Studies that recruited patients with organic constipation, drug-induced constipation, highly selected groups of patients (such as elderly patients or the institutionalised), or those that enrolled a mixture of CIC patients and those suffering from either irritable bowel syndrome (IBS) or diverticular disease, were ineligible. The minimum duration of therapy considered was 1 week. Studies had to report dichotomous data assessing response to therapy, or continuous data examining the effect of therapy on either mean number of stools per week, or mean symptom scores.
Studies on CIC were identified using the terms: constipation or gastrointestinal transit [both as medical subject headings (MeSH) and free text terms], or functional constipation, idiopathic constipation, chronic constipation, or slow transit (as free text terms). These were combined using the set operator AND with studies identified via the following terms: dietary fiber, cellulose, plant extracts, psyllium, cereals, plantago, or methylcellulose (as MeSH and free text terms), or the following free text terms: fiber, fibre, soluble fibre, insoluble fibre, bran, ispaghula, metamucil, fybogel, or ispaghula.
There were no language restrictions, and abstracts identified from the original search were evaluated by two investigators for appropriateness and, for those deemed eligible for inclusion, the full paper was obtained and evaluated. Foreign language papers were translated. Abstract books of conference proceedings published between 2002 and 2010 were also hand searched for eligible studies. A recursive search of the literature was performed using the bibliographies of identified studies. Studies were assessed independently by two investigators using predefined eligibility criteria, with disagreements resolved by discussion.
Data were extracted independently by two investigators on to a Microsoft Excel spreadsheet (XP professional edition; Microsoft Corp, Redmond, WA, USA) as dichotomous outcomes (response or no response to therapy), or mean symptom scores or mean number of stools per week during treatment. The following clinical data were also collected: setting (primary, secondary, or tertiary care), number of centres, country of origin, dose and duration of therapy, concomitant medications allowed, definition of CIC used, primary outcome measure used to define response to therapy, method used to generate the randomisation schedule and conceal treatment allocation (where reported), level of blinding and proportion of female patients. Data were extracted as intention-to-treat analyses, with all drop-outs assumed to be treatment failures. If this was not clear from the original article then we performed an analysis on all patients with reported evaluable data. Adverse events data were also extracted where reported.
Assessment of risk of bias
This was performed independently by two investigators, with disagreements resolved by discussion. By recording the methods used to generate the randomisation schedule and conceal treatment allocation, the level of blinding, the proportion of patients who completed follow-up, whether an intention-to-treat analysis was extractable, and whether there was evidence of selective reporting of outcomes, the risk of bias was assessed as described in the Cochrane handbook.17
The search strategy identified 3146 citations, of which 14 appeared to be relevant to the systematic review, and were retrieved for further evaluation. Six of these studies were eligible for inclusion (Figure 1).18–23 A formal meta-analysis was not performed due to concerns over the methodological quality and risk of bias of the studies identified. The characteristics of eligible and included trials are summarised in Table 1. Four of the eligible trials used soluble fibre. Of these, three used psyllium,19, 20, 23 and the fourth used a combination of inulin and maltodextrose.22 Two used insoluble fibre, wheat bran in one study,18 and rye bread in the other.21 The treatment period ranged from 2 to 8 weeks. No trial was at low risk of bias, and the majority was conducted in tertiary care, and recruited predominantly female patients. None of the trials allowed any active medications for the treatment of constipation to be co-administered to patients, though one study did allow a nonmedicated cleansing enema as a rescue therapy for patients who did not have a bowel motion for eight consecutive days.18 Individual trial results are provided in Table 2.
|Study||Country, setting, and number of centres||Criteria used to define CIC||Number of participants (% female)||Duration of therapy||Active intervention||Methodology|
|Fenn et al.20||UK, primary care, 17 sites||Clinical diagnosis||201 (75.1)||2 weeks||Psyllium 3.6 g t.d.s.||Randomisation and concealment unclear, single-blind|
|Ashraf et al.19||USA, tertiary care, 1 site||3 or less stools per week||22 (63.6)||8 weeks||Psyllium 5 g b.d.||Randomisation and concealment unclear, double-blind|
|Nunes et al.23||Brazil, tertiary care, number of sites not reported||Less than 3 stools per week||60 (65.0)||2 weeks||Psyllium 10 g/day||Randomisation and concealment unclear, double-blind|
|Lopez Roman et al.22||Spain, tertiary care, 3 sites||Rome II criteria||32 (87.5)||20 days||Inulin and maltodextrin 20 g/day||Randomisation and concealment unclear, double-blind|
|Badiali et al.18||Italy, tertiary care, 1 site||Clinical diagnosis and negative investigations||24 (91.7)||4 weeks||Bran 6.6 g t.d.s.||Randomisation and concealment unclear, double-blind|
|Hongisto et al.21||Finland, tertiary care, 1 site||Clinical diagnosis||29 (100)||3 weeks||320 g fibre-rich rye bread||Randomisation, concealment, and blinding unclear|
|Study||Active intervention||Criteria used to define response to therapy||Number in fibre arm||Treatment effect in fibre arm||Number in placebo/no therapy arm||Treatment effect in placebo/no therapy arm|
|Fenn et al.20||Psyllium||Proportion with an improvement in global symptoms||104||86.5%||97||47.4%|
|Ashraf et al.19||Psyllium||Increase in mean stool frequency per week||11||0.9||11||0.2|
|Nunes et al.23||Psyllium||Proportion with normalisation of evacuation||30||86.7%||30||30.0%|
|Lopez Roman et al.22||Inulin and maltodextrin||Proportion with straining during defaecation||15||35.7%||17||78.6%|
|Badiali et al.18||Bran||Proportion with no straining during defaecation||9*||55.6%||7*||28.6%|
|Hongisto et al.21||Fibre-rich rye bread||Mean number of stools per day||15||1.3||14||0.9|
Efficacy of soluble fibre in chronic idiopathic constipation
The largest identified RCT was conducted by Fenn et al.20 This single-blind trial recruited 201 patients, randomising 104 to psyllium and 97 to placebo during a 2-week treatment period. Overall, 90 (86.5%) patients allocated to psyllium reported an improvement in symptoms, compared with 46 (47.4%) patients receiving placebo (P < 0.001). The authors also reported a reduction in abdominal pain and discomfort with psyllium in those patients reporting these symptoms at baseline, with an improvement in 44 (80.0%) of 55 psyllium patients compared with 27 (64.3%) of 42 receiving placebo (P = 0.035). Finally, straining on defaecation was also reduced with psyllium, with 70 psyllium and 63 placebo patients reporting this symptom at study entry, compared with 11 and 27 at trial completion (P = 0.003).
Ashraf et al. enrolled 22 patients with CIC,19 and randomised them in equal numbers to psyllium or placebo for 8 weeks. They reported a significant increase in mean stool frequency per week following treatment with psyllium (3.8 stools per week after 8 weeks of therapy, compared with 2.9 stools per week at baseline, P < 0.05), but no such change with placebo. Patients in the active treatment arm also reported improvements in individual parameters such as stool consistency, pain on defaecation, straining and sense of complete evacuation compared with baseline, although only the former two differences were statistically significant (P < 0.05 for both).
In a Brazilian trial conducted by Nunes et al.,23 60 patients were recruited and randomised to either 10 g of psyllium per day or placebo for 2 weeks in a double-blind fashion. The primary outcome measure used to define a response to therapy was normalisation of evacuation. This was achieved in 26 (86.7%) of 30 patients receiving psyllium compared with only 9 (30.0%) of 30 patients allocated to placebo (P < 0.001).
Finally, Lopez-Roman and colleagues used 20 g of a soluble fibre mixture of inulin and maltodextrin, administered as a dairy preparation, in a placebo-controlled trial conducted in Spain.22 In total, 32 patients were randomised, with 15 allocated to fibre and 17 receiving placebo. There were significant reductions in the proportion of patients reporting straining during defaecation, sensation of incomplete evacuation and sensation of obstruction with soluble fibre (P < 0.001 for all analyses). In addition, the number of days between bowel movements was also significantly reduced (P < 0.001).
Efficacy of insoluble fibre in chronic idiopathic constipation
The first trial reporting the efficacy of insoluble fibre in CIC was conducted in Italy by Badiali et al.18 The 24 patients recruited were allocated to receive 20 g of bran per day or placebo. As this was a cross-over trial, only the first treatment period is described. Following the first 4-week period of the trial (prior to cross-over) no statistically significant difference in response, defined as having no further straining at stool, occurred with active treatment [5 (55.6%) of nine patients who reported this at baseline] compared with placebo [2 (28.6%) of 7 patients].
The second RCT carried out by Hongisto and colleagues compared four diets: rye bread with Lactobacillus GG yoghurt, rye bread alone, Lactobacillus GG yoghurt alone and low fibre bread.21 For the purposes of this systematic review, we only examined outcomes in patients randomised to rye bread alone and those given low fibre bread. The study took place over a 3-week period and recruited a total of 29 female patients in these two arms of the trial. Following the 3-week intervention period, the mean difference in number of stools per day was 0.4 for the patients randomised to rye bread compared with those assigned to low fibre bread (P = 0.001). Difficulty of defaecation was also significantly reduced with rye bread (P < 0.001), and stools were significantly softer (P < 0.001).
Adverse events with fibre
No single study reported total adverse events. One trial reported the number of patients in each trial arm who dropped out due to adverse events (one with psyllium and two with placebo).20 Ashraf et al. recorded individual adverse events, with 18% of psyllium patients experiencing abdominal pain compared with 0% of placebo patients, but no differences in back pain, bloating, or cramping.19 Finally, there were higher combined symptom scores for gastrointestinal side effects such as abdominal pain, flatulence, borborygmi and bloating with rye bread compared with low fibre toast (mean difference in scores = 1.6, P < 0.001).21
This systematic review has summarised all the available published evidence examining the efficacy of fibre in patients with CIC. Despite recommendations from both national and international guidelines that increasing dietary fibre intake should be the first-line step in the management of the condition,13, 14 the evidence for any benefit of this approach appears limited. We identified only six RCTs, none of which were at low risk of bias and the majority recruited only a small number of patients. Overall, soluble fibre may be more effective than placebo in patients with CIC. All four studies examining its efficacy,19, 20, 22, 23 three of which used psyllium,19, 20, 23 reported significant improvements in individual symptoms of CIC such as straining or pain on defaecation, stool consistency, sensation of incomplete evacuation and sensation of obstruction. In addition, mean number of stools per week increased, and number of days between bowel movements was also significantly reduced. However, the two trials examining the effects of insoluble fibre compared with placebo or low fibre bread were conflicting, with one trial demonstrating a significant difference in mean number of stools per day with active therapy, as well as reduced difficulty in defaecation and increased stool softness,21 whilst the other cross-over RCT found no significant difference in response to therapy, defined as reporting no straining at stool, with active treatment vs. placebo,18 though as the trial contained only 24 patients this may have been due to a lack of power. Adverse events were poorly reported. In one placebo-controlled trial of psyllium abdominal pain was reported more frequently among those assigned to active treatment,19 and in the study using fibre-rich rye bread, the combined symptom score for gastrointestinal side effects was higher in patients taking rye bread compared with those in the placebo arm.21
We performed this systematic review using rigorous methodology. The comprehensive literature search was conducted separately by two investigators. We included and translated non-English language publications. Data extraction was performed separately, again by two investigators, with discrepancies resolved by consensus. We also used an intention-to-treat analysis, where we assumed all drop-outs to be treatment failures, wherever possible. Limitations arise from the quality and reporting of the trials included in the systematic review. None of the trials were at low risk of bias, failing to report the method used to generate the randomisation schedule or conceal allocation in all six cases, meaning that the benefit of fibre in CIC in these RCTs may have been overestimated.24 Duration of therapy was relatively short in most instances, with only one study treating patients for more than 4 weeks.19 There was also great variation in the definitions of improvement with therapy, or primary outcome measurements, making comparisons between the trials difficult. Due to all of the above, we elected not to perform a formal meta-analysis. In addition, only one trial recruited patients from primary care,20 which is where the majority of patients with CIC will first consult a physician, and therefore the setting in which an increase in dietary fibre intake is most likely to be used as a first therapeutic manoeuvre. The fact that the majority of studies we identified, which were conducted in tertiary care, will not be generalisable to this situation is therefore of concern. Finally, the patients recruited were predominantly women, meaning that any potential benefit of fibre in men with CIC is even less clear.
There have been systematic reviews examining the efficacy of fibre in CIC published previously. The earliest of these, which performed a meta-analysis, concluded that fibre led to a modest improvement in stool frequency compared with placebo or no treatment, which was of a similar magnitude to that achieved with laxatives.25 However, the authors did not restrict their analysis to trials of patients with CIC, but also included RCTs conducted in mixed populations of IBS and CIC patients, patients with diverticular disease, and individuals in nursing homes and psychiatric units. A further meta-analysis that pooled data from placebo-controlled trials of fibre and laxatives together reported that any obvious benefit of the two over placebo could not be established.26 Finally, a systematic review published in 2005 examined the efficacy of various medical therapies, including soluble and insoluble fibre, in patients with CIC.27 The authors included head-to-head trials of fibre vs. laxatives as well as placebo-controlled trials. Some of the included RCTs included IBS patients, or were conducted in the elderly and institutionalised, posthysterectomy patients and pregnant women. No formal meta-analysis was undertaken, but the authors concluded that there was moderate evidence to support the use of psyllium in CIC, but that evidence for any benefit of insoluble fibre such as wheat bran was poor. The present systematic review provides an update to these previous studies, with half of the trials we identified being published in the intervening years,21–23 as well as restricting the analysis only to RCTs of fibre vs. placebo or no therapy, conducted among patients with true CIC.
Current national and international guidelines recommend the use of fibre in both dietary and supplement form in the early management of constipation.13, 14 However, it is apparent from the trials identified by this systematic review that there is a relative paucity of high quality evidence to support such an approach. In a recent systematic review and meta-analysis of RCTs, which were generally of higher quality than those identified in the present study, both osmotic and stimulant laxatives, as well as newer agents such as prucalopride and linaclotide, were superior to placebo in the treatment of CIC.28 Two of the largest and most rigorously designed of the RCTs included in this meta-analysis were conducted only very recently and confirmed efficacy of both bisacodyl and sodium picosulphate, two traditional, and perhaps neglected, therapies.29, 30 This emphasises the need for trials of similar quality studying the efficacy of fibre in CIC. Another recently published meta-analysis has suggested that psyllium is of benefit in IBS,31 and a high quality RCT that studied the efficacy of both soluble and insoluble fibre in IBS demonstrated that both were better than placebo.32 Some investigators have reported a significant degree of overlap between IBS and CIC,33 suggesting common pathophysiological mechanisms. This, together with the fact that previous studies have demonstrated that transit time in some constipated patients normalises with fibre,34 means that fibre supplementation should not be excluded from the management of CIC, particularly as there are likely to be few risks arising from such an approach.
In summary, this systematic review suggests that soluble fibre may be of some benefit in CIC. However, further large trials examining the efficacy of both soluble and insoluble fibre in CIC, that recruit patients from primary care, use validated outcome measures, adhere to the recommendations made by the Rome committee for the design of treatment trials in the functional GI disorders35 and those that report adverse events fully are required before any firm recommendations for the role of either soluble or insoluble fibre in the management of the condition can be made.
Declaration of personal and funding interests: None.
- 2Epidemiology of constipation (EPOC) study in the United States: relation of clinical subtypes to sociodemographic features. Am J Gastroenterol 1999; 94: 3530–40., , , et al.Direct Link:
- 13World Gastroenterology Organisation Practice Guidelines: Constipation. Available at:http://www.worldgastroenterology.org/assets/downloads/en/pdf/guidelines/05_constipation.pdf.
- 16Report of an international workshop on management of constipation. Gastroenterology Int 1991; 4: 99–113., , , .
- 17Cochrane Handbook for Systematic Reviews of Interventions: Version 5.0.2. Available at: http://www.cochrane-handbook.org., .
- 23A double-blind trial of a celandin, aloevera and psyllium laxative preparation in adult patients with constipation. Rev Bras Med 2005; 62: 352–7., , , et al.
- 27Efficacy and safety of traditional medical therapies for chronic constipation: systematic review. Am J Gastroenterol 2005; 100: 936–71., .Direct Link:
- 29Stimulant laxatives are effective in chronic constipation: multi-center, 4-week, double-blind, randomized, placebo-controlled trial of bisacodyl. Gastroenterology 2010; 138(Suppl. 1): S228., , , et al.