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© 2014 by the American College of Gastroenterology The A meri can Jour nal of GASTROENTEROLOGY
nature publishing group 1367
REVIEW
CLINICAL AND SYSTEMATIC REVIEWS
INTRODUCTION
Irritable bowel syndrome (IBS) is a relatively modern term ( 1 ) for a
lower gastrointestinal (GI) symptom complex that has been described
for centuries, with notable gures such as Beethoven possibly su er-
ing from this disorder ( 2 ). Fiber supplementation has a long history
in the management of functional lower GI disorders, although, more
recently, there has been caution expressed in the use of ber in IBS
as it may exacerbate certain symptoms in some patients ( 3 ). We have
previously conducted a systematic review of ber supplementation
in IBS and found that there was RCT evidence that this approach
did reduce overall IBS symptoms, particularly with psyllium-based
products ( 4 ). is was based on small studies that usually had an
unclear risk of bias and hence the quality of evidence was low ( 5 ).
Since then, further randomized controlled trial (RCT) evidence
( 6 ) has been published. We have therefore updated our systematic
review on ber supplementation in the treatment for IBS.
METHODS
Search strategy and study selection
A search of the medical literature was conducted using MEDLINE
(1946 to December 2013), EMBASE, and EMBASE Classic
The Effect of Fiber Supplementation on Irritable Bowel
Syndrome: A Systematic Review and Meta-analysis
Paul Moayyedi , BSc, MB, ChB, PhD, MPH, FRCP, FRCPC, AGAF, FACG
1 , Eamonn M.M. Quigley , MD, FRCP, FACP, FACG, FRCPI
2 ,
Brian E. Lacy , MD, PhD, FACG
3 , Anthony J. Lembo , MD, FACG
4 , Yuri A. Saito , MD, MPH, FACG
5 , Lawrence R. Schiller , MD, FACP, FACG
6 ,
Edy E. So er , MD, FACG
7 , Brennan M.R. Spiegel , MD, MSHS, FACG
8 and Alexander C. Ford , MB, ChB, MD
9 , 10
OBJECTIVES: Fiber has been used for many years to treat irritable bowel syndrome (IBS). This approach had fallen
out of favor until a recent resurgence, which was based on new randomized controlled trial (RCT)
data that suggested it might be effective. We have previously conducted a systematic review of fi ber
in IBS, but new RCT data for fi ber therapy necessitate a new analysis; thus, we have conducted a
systematic review of this intervention.
METHODS: MEDLINE, EMBASE, and the Cochrane Controlled Trials Register were searched up to December
2013. Trials recruiting adults with IBS, which compared fi ber supplements with placebo, control
therapy, or “ usual management ” , were eligible. Dichotomous symptom data were pooled to obtain a
relative risk (RR) of remaining symptomatic after therapy as well as number needed to treat (NNT)
with a 95 % confi dence interval (CI).
RESULTS: We identifi ed 14 RCTs involving 906 patients that had evaluated fi ber in IBS. There was a signifi cant
benefi t of fi ber in IBS (RR = 0.86; 95 % CI 0.80 – 0.94 with an NNT = 10; 95 % CI = 6 – 33). There was
no signifi cant heterogeneity between results ( I
2 = 0 % , Cochran Q = 13.85 (d.f. = 14), P = 0.46). The
benefi t was only seen in RCTs on soluble fi ber (RR = 0.83; 95 % CI 0.73 – 0.94 with an NNT = 7; 95 %
CI 4 – 25) with no effect seen with bran (RR = 0.90; 95 % CI 0.79 – 1.03).
CONCLUSIONS: Soluble fi ber is effective in treating IBS. Bran did not appear to be of benefi t, although we did not
uncover any evidence of harm from this intervention, as others have speculated from uncontrolled data.
Am J Gastroenterol 2014; 109:1367–1374; doi: 10.1038/ajg.2014.195; published online 29 July 2014
1 Health Sciences Center, Farncombe Family Digestive Health Research Institute, McMaster University , Hamilton , Ontario , Canada ;
2 Division of Gastroenterology
and Hepatology, Department of Medicine, Houston Methodist Hospital , Houston , Texas , USA ;
3 Dartmouth-Hitchcock Medical Center, Division of Gastroenterology
and Hepatology, One Medical Center Drive , Lebanon , New Hampshire, USA ;
4 The Beth Israel Deaconess Medical Center , Boston , Massachusetts , USA ;
5 Division
of Gastroenterology and Hepatology, Mayo Clinic , Rochester , Minnesota , USA ;
6 Digestive Health Associates of Texas, Baylor University Medical Center , Dallas ,
Texas , USA ;
7 Division of Gastroenterology at Cedars-Sinai, University of Southern California , Los Angeles , California , USA ;
8 Department of Gastroenterology, VA
Greater Los Angeles Healthcare System , Los Angeles , California , USA ;
9 Leeds Gastroenterology Institute, St. James ’ s University Hospital , Leeds , UK ;
10 Leeds
Institute of Biomedical and Clinical Sciences, University of Leeds , Leeds , UK . Correspondence: Paul Moayyedi, BSc, MB, ChB, PhD, MPH, FRCP, FRCPC,
AGAF, FACG , Health Sciences Center, Farncombe Family Digestive Health Research Institute, McMaster University , Hamilton , Ontario , Canada L8N 3Z5 .
E-mail: moayyep@mcmaster.ca
Received 28 February 2014; accepted 3 June 2014
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Moayyedi et al.
(1947 to December 2013), and the Cochrane central register of
controlled trials. RCTs examining the e ect of supplementing
the diet with ber in adult patients (over the age of 16 years) with
IBS were eligible for inclusion ( Box 1 ). We contacted the authors
of studies that evaluated functional GI disorders that could have
included IBS, but did not report this group of patients sepa-
rately. Similarly, we contacted original investigators of studies
that did not report dichotomous data but were otherwise eligible
for inclusion in the systematic review to explore whether these
data were available.
e literature search was performed as part of a broader exer-
cise to inform an update of the ACG monograph on the manage-
ment of IBS. Speci cally, studies on IBS were identi ed with the
terms irritable bowel syndrome a n d functional diseases, colon ( b o t h
as medical subject heading (MeSH) and free text terms), and IBS ,
spastic colon , irritable colon , o r functional a d j 5 bowel ( a s f r e e t e x t
terms). ese were combined using the set operator AND with
dietary ber , cereals , psyllium , sterculia , karaya gum (both as MeSH
terms and free text terms), or the following free text terms: bulking
agent , psyllium bre , bre , husk , bran , ispaghula , o r wheat bran .
Articles in any language were eligible and were translated when
appropriate. Abstracts were also eligible, and conference proceed-
ings from United European Gastroenterology Week and Digestive
Diseases Week between 2001 and 2013 were hand-searched to
identify potentially eligible studies published only in abstract form.
We also performed a recursive search of the literature from the
bibliographies of all relevant studies retrieved from the electronic
search. Two masked reviewers assessed potentially relevant articles
using predesigned eligibility forms, according to the prospectively
de ned eligibility criteria ( Box 1 ). We resolved any disagreement
between investigators by consensus.
Outcome assessment
e primary outcome was de ned as global improvement in IBS
symptoms. If this was not available then improvement in abdom-
inal pain was taken as the primary outcome. When more than
one de nition was provided for improvement in the primary
outcome, the most stringent de nition with the lowest placebo
response rate was taken. Secondary outcomes included quality of
life and adverse events.
Data extraction
Two reviewers independently recorded data from eligible stud-
ies onto a Microso Excel spreadsheet (XP professional edition;
Microso , Redmond, WA). In addition to the primary outcome
( Box 2 ), the following clinical data were extracted for each trial:
setting (primary, secondary, or tertiary care-based), number
of centers, country of origin, type of ber supplementation,
duration of therapy, total number of adverse events reported,
criteria used to de ne IBS, primary outcome measure used to
de ne symptom improvement or cure following therapy, dura-
tion of follow-up, proportion of female patients, and propor-
tion of patients according to predominant stool pattern. Data
were extracted as intention-to-treat analyses, with all dropouts
assumed to be treatment failures, whenever trial reporting
allowed this.
Assessment of risk of bias
Two independent reviewers assessed the risk of bias using the
Cochrane handbook risk of bias tool ( 7 ). is evaluates the
method of randomization, whether allocation was concealed,
method of blinding, the completeness of follow-up, whether there
was evidence of selective outcome reporting, and other biases.
Box 1. Eligibility criteria
Randomized controlled trials
Adults (participants aged > 16 years)
Diagnosis of irritable bowel syndrome (IBS) based on either a clinician ’ s opinion or meeting specifi c diagnostic criteria (Manning,
Kruis score, Rome I, II, or III).
Compared fi ber supplementation with placebo or no therapy.
Minimum duration of therapy 7 days.
Minimum duration of follow-up 7 days.
Dichotomous assessment of response to therapy in terms of effect on global IBS symptoms or abdominal pain following therapy
(Preferably patient-reported, but if this was not available then as assessed by a physician or questionnaire data.).
Box 2. Data extraction methodology
Outcome of interest: improvement in global irritable bowel syndrome (IBS) symptoms preferable; if not reported then improve-
ment in abdominal pain.
Reporting of outcomes: patient-reported preferable; if not available then investigator-reported.
Time of assessment: upon completion of therapy.
Denominator used: true intention-to-treat analysis; if not available then all evaluable patients.
Cutoff used for dichotomization: any improvement in global IBS symptoms or abdominal pain for Likert-type scales, investigator-de-
fi ned improvement for continuous scales; if no investigator defi nition was available we used ≥ 1 s.d. decrease in symptom score from
baseline to completion of therapy (we assessed whether the use of any decrease in symptom score from baseline to completion of
therapy altered our analysis).
© 2014 by the American College of Gastroenterology The A meri can Jour nal of GASTROENTEROLOGY
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Fiber Supplementation in IBS
with two at high risk ( 19,12 ); the remaining were unclear. Eleven
trials used a “ clinical diagnosis ” of IBS supplemented by negative
investigations to de ne the condition, with only one study using
the Manning criteria combined with negative investigations ( 20 ),
one the Rome I criteria combined with negative investigations
( 24 ), and one the Rome III criteria ( 12 ).
ere was a statistically signi cant e ect in favor of ber com-
pared with placebo (RR of IBS not improving = 0.86; 95 % CI
0.80 – 0.94, Figure 2 ) w i t h a n n u m b e r n e e d e d t o t r e a t o f 1 0 ( 9 5 %
CI = 6 – 33). ere was no signi cant heterogeneity between results
( I 2 = 0 % , C o c h r a n Q = 1 3 . 8 5 ( d . f . = 1 4 ) , P = 0 . 4 6 ) . S u b g r o u p a n a l y -
sis showed no major di erences in e cacy according to duration
of therapy, de nition of IBS, and various quality criteria, includ-
ing the proportion of subjects followed up, whether the study was
double-blind, whether the method of randomization was stated,
and whether the study had a low, unclear, or high risk of bias
( Ta bl e 2 ) .
Bran vs. soluble fi ber
Six studies used bran in a total of 441 patients (6, 12, 13, 18, 19,
23), seven studies used ispaghula husk in a total of 499 patients
( 6,15 – 18,21,22 ), and the remaining studies used “ concentrated
ber ” ( 23 ), or linseeds ( 12 ). Bran had no statistically signi cant
e ect on the treatment of IBS (RR of IBS not improving = 0.90;
95 % CI 0.79 – 1.03, P = 0.14; Figure 2 ), but ispaghula was e ective
in treating IBS symptoms (RR of IBS not improving = 0.83; 95 % CI
0.73 – 0.94, P = 0.005; Figure 2 ). e number needed to treat with
ispaghula was 7 (95 % CI 4 – 25). Numerically the risk ratio was not
Data synthesis and statistical analysis
Global IBS symptoms or abdominal pain persisting with interven-
tion compared with control was expressed as a relative risk (RR)
with 95 % con dence intervals (CIs). Data were pooled using a
random-e ects model ( 8 ) to allow for any heterogeneity between
studies. Adverse events data were also summarized with RRs. e
number needed to treat and the number needed to harm, with
95 % CIs, were calculated from the reciprocal of the risk di erence
of the meta-analysis.
H e t e r o g e n e i t y b e t w e e n s t u d i e s w a s a s s e s s e d u s i n g b o t h t h e
I 2 - s t a t i s t i c w i t h a c u t o of ≥ 5 0 % a n d t h e χ 2 - t e s t w i t h a P v a l u e < 0 . 1 0 ,
used to de ne a signi cant degree of heterogeneity ( 9 ). When the
degree of statistical heterogeneity was greater than this between
trial results in this meta-analysis, possible explanations were inves-
tigated using subgroup analyses according to type of intervention,
trial setting, criteria used to de ne IBS, whether method of ran-
domization or concealment of allocation was reported, level of
blinding, and risk of bias of included trials. We compared indi-
vidual RRs between these analyses using the Cochran Q - s t a t i s t i c .
ese were exploratory analyses only and may explain some of the
observed variability, and hence the results should be interpreted
with caution.
R e v i e w M a n a g e r v e r s i o n 5 . 1 . 4 ( R e v M a n f o r W i n d o w s 2 0 0 8 , t h e
Nordic Cochrane Centre, Copenhagen, Denmark) and StatsDirect
version 2.7.7 (StatsDirect, Sale, Cheshire, UK) were used to gener-
ate Forest plots of pooled RRs and RDs for primary and secondary
outcomes with 95 % CIs, as well as funnel plots. e latter were
assessed for evidence of asymmetry, and therefore for possible
publication bias or other small study e ects, using the Egger test
( 10 ), if there were 10 or more eligible studies included in the meta-
analysis ( 11 ).
RESULTS
e search strategy identi ed a total of 343 citations, of which
29 were evaluated and 14 were eligible for the systematic review
( Figure 1 ). e agreement between reviewers regarding eligibil-
ity for inclusion in the review was perfect ( κ - s t a t i s t i c = 1 . 0 ) . is
update of our previous systematic review and meta-analysis on
ber in IBS ( 5 ) identi ed an additional two studies ( 6,12 ), which
increased the number of patients included in the analysis substan-
tially.
Overall effi cacy of fi ber supplementation in the treatment
of IBS
ere were 14 RCTs ( 6,12 – 24 ) involving 906 patients. A summary
of the eligible trials is given in Ta b le 1 . e majority of trials did
not di erentiate between the type of IBS patients recruited, with
only ve studies providing data on this ( 6,12,21 – 24 ), two of which
recruited only IBS-C patients. ( 23,24 ). e proportion of women
in trials ranged between 20 and 90 % . Ten trials were double-blind
(6,13,15 – 18,20 – 23), two were single blind ( 14,24 ), and two were
open label ( 19,12 ), but only four reported adequate methods of
randomization ( 6,14,15,12 ) and only one described adequate con-
cealment of allocation ( 6 ). Only one trial was at low risk of bias ( 6 ),
343 Papers
identified by the
search
- 6 No placebo arm
- 5 Data not extractable
- 2 Not IBS
- 1 No fiber arm
- 1 Duplicate
14 Papers eligible
15 Papers excluded
Figure 1 . Flow diagram of assessment of studies identifi ed in the updated
fi ber and irritable bowel syndrome (IBS) systematic review and meta-
analysis.
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Table 1 . Characteristics of randomized controlled trials (RCTs) of fi ber vs. placebo in irritable bowel syndrome (IBS)
Author Design Participants Interventions Methodology Outcomes
Soltoft et al. ( 13 ) Danish RCT,
single center
Author-defi ned IBS. 59
Patients from tertiary
care. 64 % female
Miller’s bran biscuits vs.
wheat biscuits for
6 weeks.
Laxatives allowed as
rescue medication
Method of randomization and
concealment of allocation not
stated. Double-blind. 12 %
Loss of follow-up. No selective
reporting
Global assessment of
IBS symptoms on Likert
scale. Much or slightly
improved from baseline
symptoms
Manning et al. ( 14 ) English RCT,
single center
Author-defi ned IBS.
26 Patients recruited
from tertiary care. 46 %
Female
60 ml Unprocessed
wheat bran or 170 g
whole-wheat bread daily
vs. low-fi ber diet for 6
weeks.
Unclear if other IBS
medications allowed
Method of randomization stated.
Method of concealment of
allocation not stated. Investigator-
blinded. 8 % Loss of follow-up.
No selective reporting
Percentage of days on
which pain charted by
patient in special chart.
Improvement in
percentage of day’s
pain charted before and
after study
Ritchie and Truelove
( 15 )
English RCT,
single center
Author-defi ned IBS.
100 Patients recruited
from tertiary care. 77 %
Female.
Ispaghula husk vs.
placebo for 3 months.
Unclear if other IBS
medications allowed
Method of randomization stated.
Method of concealment of alloca-
tion not stated. Double-blind. 4 %
Loss of follow-up. No selective
reporting
Dichotomous assess-
ment of IBS symptoms:
“ improved ” or “ not
improved ”
Longstreth et al. ( 16 ) US RCT, single
center
Author-defi ned IBS. 77
Patients recruited from
secondary care. 83 %
Female
Ispaghula vs. placebo
for 8 weeks. No other
IBS medications al-
lowed
Method of randomization and
concealment of allocation not
stated. Double-blind. 22 %
Loss of follow-up. No selective
reporting
Global assessment of
IBS symptoms on Likert
scale. Much or a little
better from baseline
symptoms
Arthurs and Fielding
( 17 )
Irish RCT,
single center
Author-defi ned IBS. 80
Patients recruited from
secondary care. 78 %
Female.
Ispaghula husk vs.
placebo for 4 weeks.
Unclear if other IBS
medications allowed
Method of randomization and
concealment of allocation not
stated. Double-blind. 2.5 %
Loss of follow-up. No selective
reporting
Global assessment of
IBS symptoms on Likert
scale. Resolved or
improved from baseline
symptoms
Nigam et al. ( 18 ) Indian RCT,
single center
Author-defi ned IBS.
168 Patients recruited
from secondary care.
45 % Female
Ispaghula husk vs.
placebo for 3 months.
Unclear if other IBS
medications allowed
Method of randomization
and concealment of allocation
not stated. Double-blind.
Apparently no one lost to
follow-up. No selective reporting
Dichotomous
assessment of IBS:
“ improved ” or “ not
improved ”
Kruis et al.
( 19 ) German RCT,
single center
Author-defi ned IBS.
120 Patients recruited
from tertiary care.
62.5 % Female
15 g wheat bran per
day vs. placebo for 16
weeks. No other IBS
medications allowed
Method of randomization and
concealment of allocation not
stated. Unblinded. 17.5 %
Loss of follow-up. No selective
reporting
Global assessment of
IBS symptoms on Likert
scale. Disappeared or
improved from baseline
symptoms
Lucey et al. ( 20 ) English RCT,
single center
Manning IBS. 44
Patients recruited from
tertiary care. 79 %
Female
Bran biscuits vs.
placebo biscuits for
3 months. Unclear if
other IBS medications
allowed
Method of randomization and
concealment of allocation not
stated. Double-blind. 36 %
Loss of follow-up. No selective
reporting
Total IBS questionnaire
symptom score (unclear
if validated). Lower
score after treatment
indicated symptom
improvement
Prior and Whorwell ( 21 ) English RCT,
single center
Author-defi ned IBS. 80
Patients recruited from
tertiary care. 49 % Con-
stipation predominant.
90 % Female
Ispaghula husk vs.
placebo for 12 weeks.
Unclear if other IBS
medications allowed
Method of randomization and
concealment of allocation not
stated. Double-blind. 29 %
Loss of follow-up. No selective
reporting
Overall improvement in
well-being discussed
with patient, and rated
as “ satisfactory ” or
“ unsatisfactory ”
Jalihal and Kurian ( 22 ) Indian RCT,
single center
Author-defi ned IBS.
22 Patients recruited
from secondary care.
20 % Female. 25 %
had
constipation, 75 % had
diarrhea
Ispaghula husk vs.
placebo for 4 weeks. No
other IBS medications
allowed
Method of randomization and
concealment of allocation not
stated. Double-blind. 9 % Loss of
follow-up. No selective reporting
Dichotomous assess-
ment of IBS:
“ improved ” or “ no
change ”
Fowlie et al. ( 23 ) Scottish RCT,
single center
Author-defi ned IBS. 51
Patients recruited from
tertiary care. 100 %
Constipation predomi-
nant or mixed.
65 % Female
Concentrated fi ber vs.
placebo for 3 months.
Unclear if other IBS
medications allowed
Method of randomization and
concealment of allocation not
stated. Double-blind. 14 %
Loss of follow-up. No selective
reporting
Global assessment
of IBS symptoms on
Likert scale. Generally
better from baseline
symptoms
Table 1 continued on following page
© 2014 by the American College of Gastroenterology The A meri can Jour nal of GASTROENTEROLOGY
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Fiber Supplementation in IBS
Table 1 . Continued.
Author Design Participants Interventions Methodology Outcomes
Rees et al. ( 24 ) English RCT,
number
of centers
unclear
Rome I IBS. 28 Patients
recruited from tertiary
care. 100 % Constipa-
tion predominant.
Unclear what proportion
were female
10 – 20 g Of coarse
wheat bran per day
vs. placebo for 8 – 12
weeks. Unclear if
other IBS medications
allowed
Method of randomization and
concealment of allocation not
stated. Patient-blinded. 21 %
Loss of follow-up. No selective
reporting
Patients interviewed
using a questionnaire
(unclear if validated)
asking if any perceived
improvement in symp-
toms
Bijkerk et al. ( 6 ) Dutch RCT,
multicenter
Author-defi ned or Rome
II IBS.
275 Patients recruited
from primary care. C
56 % , D 25 % , M 19 %
79 % Female
20 g Ispaghula husk or
20 g bran per day vs.
placebo for 12 weeks.
Unclear if other IBS
medications allowed
Method of randomization and
concealment of allocation stated.
Double-blind. 40 % Loss to fol-
low-up. No selective reporting
Adequate relief of IBS-
related abdominal pain
or discomfort in the last
week, with responders
defi ned as those with
adequate relief for 2 out
of the last 4 weeks
Cockerell et al. ( 12 ) English RCT,
number
of centers
unclear
Rome III IBS. 40
Patients Recruited
From Primary And
Secondary Care. C
34 % , D 37.5 % 66 % Fe
24 g Linseeds per day
for 4 weeks vs. no
treatment for 4 weeks.
Other IBS medications
allowed
Method of randomization stated,
concealment of allocation not
stated. Unblinded. 30 % Loss to
follow-up. No selective reporting
Decrease of 50 points
in the IBS-symptom
severity score
Study or subgroup
Bran
Soltoft, 1976
Manning, 1977
Kruis, 1986
Lucey, 1987
Rees, 2005
Bijkerk, 2009
Subtotal (95% Cl)
Total events
Heterogeneity: !2 = 0.00; "2 = 2.76, d.f. = 5 (P = 0.74); l2 = 0%
Test for overall effect: Z = 1.47 (P = 0.14)
Total events
Heterogeneity: not applicable
Test for overall effect: Z = 1.75 (P = 0.08)
Heterogeneity: !2 = 0.01; "2 = 7.32, d.f. = 6 (P = 0.29); l2 = 18%
Test for overall effect: Z = 2.80 (P = 0.005)
Ispaghula
Linseeds
Fibre (unspecified)
Cockerell, 2012
Fowlie, 1992
Subtotal (95% Cl)
Total events
Total (95% Cl)
Total events
Heterogeneity: not applicable
Heterogeneity: !2 = 0.00; "2 = 13.85, d.f. = 14 (P = 0.46); l2 = 0%
Test for overall effect: Z = 3.50 (P = 0.0005)
Test for subgroup differences: "2 = 3.95, d.f. = 3 (P = 0.27), l2 = 24.1%
Test for overall effect: Z = 0.79 (P = 0.43)
Subtotal (95% Cl)
Ritchie, 1979
Longstreth, 1981
Arthurs, 1983
Nigam, 1984
Prior, 1987
Jalihal, 1990
Bijkerk, 2009
Subtotal (95% Cl)
Total events
17
7
29
3
6
66
32
14
40
14
14
97
211
12
7
28
4
7
75
133128
27
12
40
14
14
93
200
2.4%
1.3%
8.6%
0.4%
1.0%
23.5%
37.2%
7
17
11
13
33
2
60
143
12
37
40
21
40
11
85
12
16
14
21
37
3
178
75
246
12
40
38
21
40
9
93
253
2.9%
2.5%
1.6%
5.9%
23.8%
0.3%
23.3%
60.2%
1.20 (0.70, 2.04) 1976
1977
1986
1987
2005
2009
1979
1981
1983
1984
1987
1990
2009
0.86 (0.42, 1.74)
1.04 (0.78, 1.37)
0.75 (0.20, 2.75)
0.86 (0.39, 1.91)
0.84 (0.71, 1.00)
0.90 (0.79, 1.03)
0.60 (0.37, 0.97)
9 27 8 13 1.4% 20120.54 (0.27, 1.07)
27
98
13 1.4% 0.54 (0.27, 1.07)
10 25 7 24 1.1%
1.1%
0.1 0.2
Favors fiber Favors control
0.5 1 2 5 10
19921.37 (0.62, 3.01)
25
10
290
509
326
490 100.0% 0.86 (0.80, 0.94)
7
24 1.37 (0.62, 3.01)
1.15 (0.69, 1.92)
0.75 (0.39, 1.43)
0.63 (0.45, 0.88)
0.89 (0.75, 1.05)
0.55 (0.11, 2.59)
0.88 (0.74, 1.04)
0.83 (0.73, 0.94)
Fiber
Events Total Events Total Weight
Risk Ratio Risk ratio
M-H, random, 95% Cl M-H, random, 95% ClYear
Placebo or no treatment
Figure 2 . Forest plot of randomized controlled trials (RCTs) of fi ber vs. placebo or no treatment in irritable bowel syndrome (IBS).
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Moayyedi et al.
dramatically di erent between bran and soluble ber but this is
driven by one trial ( 6 ). is trial also concluded that soluble ber
was superior to bran, but this is not as apparent in the meta-analy-
sis as there was a statistically signi cant e ect of bran at week 12
but no e ect at weeks 4 and 8. Bran was statistically signi cant at
week 12 largely because responders remained stable from weeks 8
to 12, whereas the placebo response fell. When this study ( 6 ) was
excluded there was no e ect of bran on IBS symptoms (RR = 1.02;
95 % CI = 0.82 – 1.27). Similarly when week 8 of therapy was used
for this trial ( 6 ) rather than week 12, there was no trend toward
bene t of bran (RR = 0.98; 95 % CI = 0.85 – 1.13).
Safety of fi ber
Data on overall adverse events were provided only by six trials
( 6,18,19,21,23,12 ). ese trials evaluated a total of 566 patients,
with 130 (38.8 % ) of 335 patients receiving ber reporting
adverse events, compared with 63 (27.3 % ) of 231 in the placebo
arms. Overall, there was no statistically signi cant increase in
adverse events with ber compared with placebo (RR of adverse
event = 1.06; 95 % CI 0.92 – 1.22). When only trials that used ispa-
ghula were included in the analysis, the RR of adverse events was
1.14 (95 % CI 0.94 – 1.38), and when only RCTs of bran were con-
sidered the RR was 0.97 (95 % CI 0.79 – 1.20).
DISCUSSION
We have updated our previous systematic review and meta-analysis
( 10 ) of ber supplementation as a treatment for IBS. Our previous
systematic review identi ed 12 papers evaluating 591 IBS patients
and found that soluble, but not insoluble, ber was e ective in
reducing overall symptoms. e monograph that evaluated this sys-
tematic review was criticized ( 25 ) as it o en evaluated small studies
of poor quality. Indeed the ber data it incorporated were based on
a relatively small number of participants; thus, the 95 % CIs were
wide and relied on studies of suboptimal quality with none achiev-
ing a low risk of bias. Since the publication of that systematic review
( 4 ) there has been another RCT ( 6 ) that by itself includes more than
half the sample size of the original systematic review. Together with
another small trial ( 12 ) the updated systematic review suggests
once again that soluble ber is e ective in treating IBS symptoms,
but with more con dence than previously reported.
O u r c o n c l u s i o n i s d i erent from the Cochrane systematic
review evaluating ber in IBS ( 26 ). is review found that there
was no bene t of either type of ber in IBS, although there was a
trend toward bene t for soluble ber. is review is now 5 years
old and has not included the large trial ( 6 ) that was reported sub-
sequently. It is, however, interesting that we had suggested in our
previous review ( 4 ) that soluble ber was e ective in IBS using the
Table 2 . Subgroup analysis of randomized controlled trials of fi ber vs. placebo in IBS
Parameter No. of papers No. of patients
a
Relative risk (95 % CI) Heterogeneity
Duration of therapy
≥ 12 Weeks 9 529 0.86 (076 – 0.96) I
2 =13 % , χ
2 P =0.33
≤ 8 Weeks 6
b 458
b 0.84 (0.69 – 1.02) I
2 =8 % , χ
2 P =0.36
Defi nition of IBS
Author defi ned 10 535 0.88 (0.75 – 1.03) I
2 =25 % , χ
2 P =0.21
Manning / Rome 4 274 0.85 (0.72 – 1.00) I
2 =0 % , χ
2 P =0.59
Completeness of follow
≥ 80 % Follow 8 378 0.84 (0.67 – 1.06) I
2 =35 % , χ
2 P =0.15
< 80 % Follow 6 431 0.88 (0.79 – 0.99) I
2 =0 % , χ
2 P =0.69
Masking
Double blind 10 635 0.85 (0.75 – 0.97) I
2 =14 % , χ
2 P =0.31
Single blind 2 54 0.86 (0.50 – 1.46) I
2 =0 % , χ
2 P =1.00
Not blind 2 120 0.81 (0.43 – 1.52) I
2 =68 % , χ
2 P =0.08
Randomization
Adequate 3 228 0.83 (0.69 – 1.00) I
2 =6 % , χ
2 P =0.34
Unclear 11 581 0.89 (0.77 – 1.02) I
2 =12 % , χ
2 P =0.33
Risk of bias
Low 1 178 0.88 (0.74 – 1.04) Not applicable
Unclear / high 13 631 0.86 (0.75 – 0.99) I
2 =13 % , χ
2 P =0.32
CI, confi dence interval; IBS, irritable bowel syndrome.
a Bijkerk et al. ( 6 ) had two intervention arms, bran and psyllium — only the psyllium arm was used in subgroup analyses.
b Studies that provided earlier time points to complete this fi eld were used but this only applied to Bijkerk et al. ( 6 ). This study was used in both the ≤ 8-week and
≥ 12-week analyses using the 8- and 12-week time point data as appropriate.
© 2014 by the American College of Gastroenterology The A meri can Jour nal of GASTROENTEROLOGY
1373
REVIEW
Fiber Supplementation in IBS
conclusions drawn from it. ere remains a paucity of high-qual-
ity studies, and additional trials using modern designs optimized
to reduce bias may a ect our estimate of e ect size. In particular,
studies to evaluate the impact of ber in speci c IBS subgroups
may demonstrate di erent e ects in distinct symptom subgroups.
Additional weaknesses of existing studies include variations in a
number of clinical factors, such as the de nition of IBS, settings,
and duration of therapy. It is reassuring, however, that subgroup
analyses do not suggest that these factors have a major impact on
the conclusions of the review.
In summary, our analyses of these data suggest that there is
moderate-quality evidence that ber is e ective in IBS. Given that
ber is inexpensive and generally thought to be safe (especially
compared with the available drugs approved for IBS), ber sup-
plementation should remain a useful rst-line approach for man-
aging IBS patients.
ACKNOWLEDGMENTS
is study was performed to inform the American College of
Gastroenterology Monograph on irritable bowel syndrome.
CONFLICT OF INTEREST
Guarantor of the article : Paul Moayyedi, BSc, MB, ChB, PhD,
MPH, FRCP, FRCPC, AGAF, FACG.
Speci c author contributions : P.M., E.M.M.Q., B.E.L., A.J.L., Y.A.S.,
L.R.S., E.E.S., B.M.R.S., and A.C.F. conceived the study. P.M. and
A.C.F. collected all data. P.M. and A.C.F. analyzed and interpreted the
data. P.M. dra ed the manuscript. All authors commented on dra s of
the paper. All authors have approved the nal dra of the manuscript.
Financial support : is study was supported by the American
College of Gastroenterology.
Potential competing interests : None.
Study Highlights
WHAT IS CURRENT KNOWLEDGE
3 Fiber supplementation has been used to treat irritable
bowel syndrome (IBS).
3 We have conducted a systematic review that indicated this
approach may be effi cacious but evidence was of low quality.
WHAT IS NEW HERE
3 There is now considerably more randomized trial evidence
on fi ber and IBS.
3 Fiber supplementation is effective in improving global IBS
symptoms.
3 The effect of fi ber in IBS appears to be limited to soluble
fi ber.
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