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Oats and bowel disease: a systematic literature review
Frank Thies
1
*, Lindsey F. Masson
2,3
, Paolo Boffetta
4,5
and Penny Kris-Etherton
6
1
Division of Applied Medicine, University of Aberdeen, Polwarth Building, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK
2
Division of Applied Health Sciences, University of Aberdeen, Polwarth Building, Foresterhill, Aberdeen AB25 2ZD,
Scotland, UK
3
School of Pharmacy and Life Sciences, Robert Gordon University, Riverside East, Garthdee Road, Aberdeen AB10 7GJ,
Scotland, UK
4
The Tisch Cancer Institute and Institute for Translational Epidemiology, Icahn School of Medicine at Mount Sinai, New York,
NY 10029, USA
5
International Prevention Research Institute, 69006 Lyon, France
6
Department of Nutritional Sciences, Pennsylvania State University, University Park, PA 16802, USA
(Submitted 4 October 2013 – Final revision received 2 June 2014 – Accepted 17 June 2014)
Abstract
Whole-grain foods such as oats may protect against colorectal cancer and have benefits on inflammatory bowel disease and coeliac disease.
The present study aimed to systematically review the literature describing intervention studies that investigated the effects of oats or oat
bran on risk factors for bowel disease. A literature search was conducted using Embase, Medline and the Cochrane library, which identified
654 potential articles. Thirty-eight articles describing twenty-nine studies met the inclusion criteria. Two studies carried out in participants
with a history of colorectal adenomas found no effects of increased oat-bran intake on indirect risk makers for colorectal cancer. One of
two interventions with oat bran in patients with ulcerative colitis showed small improvements in the patients’ conditions. Most of the eleven
studies carried out in adults with coeliac disease showed no negative effects of uncontaminated oat consumption. The fourteen studies
carried out in volunteers with no history of bowel disease suggest that oats or oat bran can significantly increase stool weight and decrease
constipation, but there is a lack of evidence to support a specific effect of oats on bowel function compared with other cereals. A long-term
dietary intake of oats or oat bran could benefit inflammatory bowel disorders, but this remains to be proven. A protective effect on color-
ectal adenoma and cancer incidence has not yet been convincingly shown. The majority of patients with coeliac disease could consume up
to 100 g/d of uncontaminated oats, which would increase the acceptability of, and adherence to, a gluten-free diet.
Key words: Oats: Bowel disease: Inflammatory bowel disease: Coeliac disease: Bowel cancer
Bowel disease represents a wide spectrum of pathologies
affecting the small intestine, colon and rectum. It includes
not only minor conditions such as irritable bowel syndrome
(IBS) but also colorectal cancers and various types of
inflammatory disorders. The latter are represented by some
autoimmune disorders without clearly defined causes such
as Crohn’s disease (CD) and ulcerative colitis (UC) or others
specifically triggered by food components such as coeliac
and non-coeliac disease.
IBS produces often similar symptoms to those of inflamma-
tory bowel disease (IBD), which includes CD and UC, but as
they are not the same condition they involve very different
treatments. IBS is a functional gastrointestinal disorder (and
does not cause inflammation), which results in chronic
abdominal pain or discomfort and diarrhoea, constipation or
alternating bouts of the two. However, people with UC or
CD are also more likely to have other functional disorders
such as fibromyalgia, chronic fatigue syndrome, chronic
pelvic pain and temporomandibular joint disorder. Further-
more, UC and CD cause destructive chronic inflammation to
the intestines that could lead to permanent damage of the
intestines and harmful complications, and might require
surgery and/or pharmacological treatment with steroids or
immunosupressives.
UC affects only the colon while CD can affect any part of
the digestive tract. In addition to the clinical evaluation for
their diagnosis using imaging and endoscopic procedures,
the measurement of biomarkers such as Perinuclear Anti-
Neutrophil Cytoplasmic Antibodies for UC and Anti-Saccharo-
myces Cerevisiae Antibody for CD, along with C-reactive
protein, calprotectin and lactoferrin, can help differentiate
between both inflammatory disorders. However, these tests
*Corresponding author: F. Thies, fax þ44 1224 554761, email f.thies@abdn.ac.uk
Abbreviations: CD, Crohn’s disease; IBD, inflammatory bowel disease; IBS, irritable bowel syndrome; RCT, randomised controlled trials; UC, ulcerative
colitis.
British Journal of Nutrition (2014), 112, S31–S43 doi:10.1017/S0007114514002293
qThe Authors 2014
British Journal of Nutrition
are not conclusive. In some cases, patients have none of those
antibodies, or both, and further tests for other antibodies (anti-
OmpC, anti-CBir1, etc.) can be performed to help differentiate
between those disorders.
Bowel cancer, for which environmental factors such as diet
play a critical role
(1)
, is the third most common cancer world-
wide after lung and breast
(2)
. A recent systematic review on
prospective observational studies evaluating the associations
between dietary fibre, whole grains and risk of colorectal
cancer indicates that a high intake of dietary fibre, in particu-
lar, cereal fibre and whole grains, is associated with a reduced
risk of colorectal cancer: relative risk 0·90 (95 % CI 0·83, 0·97)
for each 10 g/d intake of cereal fibre, and relative risk 0·83
(95 % CI 0·78, 0·89) for an increment of three servings daily
of whole grains
(3)
. Whole grains are a major source of several
vitamins, minerals and phytochemicals that have anticancer
properties and could possibly influence the risk of colorectal
cancer by various potential mechanisms
(4)
. However, the
chemical composition of whole-grain foods varies greatly
and could differentially influence the activity and composition
of the gut microbiota (DJ Rose, in this supplement), and their
potential protective effects against cancer and other chronic
diseases. Therefore, it is possible that particular whole-grain
foods such as oats affect various health outcomes, particularly
with regard to bowel-related disorders.
This is also relevant for inflammatory bowel disorders.
Europe has the highest annual incidence of IBD, with 24·3
cases per 100 000 person-years and 12·7 cases per 100 000
person-years for UC and CD, respectively
(5)
. The link between
diet and IBD is not clear, but butyrate, a SCFA produced from
the colonic fermentation of dietary fibres, has been shown
to be effective in the reduction of UC
(6)
and CD
(7)
, which
suggests potential benefits for dietary interventions aiming to
increase the production of butyrate and/or other SCFA from
the gut microflora.
Coeliac disease is common, occurring in about 1 % of the
population worldwide
(8,9)
. It is traditionally characterised by
chronic inflammation of the proximal small intestine that can
develop in genetically susceptible people exposed to gluten.
The symptoms associated with coeliac disease can affect any
area of the body, and differ greatly between individuals, but
usually include headaches, diarrhoea, stomach pains and
lethargy, associated with sudden or unexpected weight loss
and unexplained Fe-deficiency anaemia, or other unspecified
anaemia. Some patients can also develop dermatitis herpeti-
formis, which is a chronic blistering skin condition. Coeliac
disease is diagnosed by blood test (for the presence of endo-
mysial antibodies and tissue transglutaminase antibodies) and
biopsy of the small intestine. The disease induces morphologi-
cal changes of the small intestine lining showing atrophy of
the villi with crypt hyperplasia, and lymphocyte infiltration,
leading to nutrient malabsorption.
The treatment of coeliac disease requires life-long adher-
ence to a gluten-free diet. Oats, compared with wheat,
barley and rye, contain low levels of prolamins, the com-
ponents of gluten responsible for the toxicity in susceptible
individuals, and could therefore represent a good source of
fibre in a gluten-free diet. Importantly, several coeliac disease
organisations support, and clinical studies suggest, that oats
may be consumed by adults and children with coeliac disease
without adverse events
(10 – 13)
.
The purpose of the present study was to systematically
review the literature describing intervention studies that had
investigated the effect of long-term consumption of whole-
grain oat-based products (including oat bran) on risk factors
for bowel disease. The objectives of the study were (1) to
summarise the large body of literature on the subject, (2) to
describe the relative strengths and weaknesses of the studies
and (3) to evaluate the need for large intervention trials.
Methods
Literature search
Embase, Medline and the Cochrane library (Cochrane Central
Register of Controlled Trials) were searched for articles
describing intervention studies with oat-based products
Table 1. Embase Classic þEmbase search strategy (1947 to 26 November 2012)
No. Search Results
1 (oat or oats or oatcake$ or flapjack$ or oatmeal or porridge or muesli or granola).mp.* 9793
2 (intervention$ or trial$).mp. 1 897 864
3 intervention study/or early intervention/ 21 882
4 ‘randomized controlled trial (topic)’/or controlled clinical trial/or ‘phase 2 clinical trial
(topic)’/or ‘clinical trial (topic)’/or ‘phase 1 clinical trial (topic)’/or
‘controlled clinical trial (topic)’/or ‘phase 3 clinical trial (topic)’/
439 432
52or3or4 1 897 864
6 1 and 5 1013
7 limit 6 to (human and english language and yr ¼‘1965 –Current’) 695
8 limit 7 to (embryo ,first trimester .or infant ,to one year .or child
,unspecified age .or preschool child ,1 to 6 years .or school child
,7 to 12 years .or adolescent ,13 to 17 years .)
87
9 7 not 8 608
10 limit 9 to (editorial or ‘review’) 79
11 9 not 10 529
12 limit 11 to (meta analysis or ‘systematic review’) 8
13 11 not 12 521
*mp¼title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer, device trade
name, keyword.
F. Thies et al.S32
British Journal of Nutrition
published before 26 November 2012. The search was limited
to full-text English language articles carried out in human sub-
jects aged 18 years or over, and excluded editorials, reviews
and meta-analyses. Table 1 shows the search terms used,
limits applied and number of articles identified in Embase.
Similar searches were carried out in Medline and the Cochrane
library databases. Additional articles were identified by search-
ing for ‘oat(s)’ in the title of references in relevant articles
obtained from the database search.
Study selection
The three databases identified a combined total of 1174
articles, of which 520 were duplicates (Fig. 1). Titles and
abstracts of the remaining 654 articles were reviewed indepen-
dently by two reviewers to identify articles describing studies
that assessed the effect of oat consumption on the risk of
bowel diseases. Articles were excluded if the studies were
conducted in children or animals, if the intervention involved
a cereal that was not oats, if the study was investigating (non-)
oat cell carcinoma or if the article used OAT as an abbre-
viation, e.g. for oral anticoagulant therapy, occluded
artery trial, oligoasthenoterato-zoospermia or organic anion
transporter. The two reviewers agreed that the full text
should be obtained for 244 articles.
Of these 244 articles, a further thirty-two articles were
excluded because the full text was not in English, the article
did not describe an intervention study, the intervention did
not involve oats or OAT was used as an abbreviation. We
excluded conference abstracts, articles describing studies in
which the intervention was less than 7 d (2- or 3-d interven-
tions (n3) and test meals (n25)), and articles in which the
effect of oats alone could not be determined or the outcomes
were not relevant. Articles describing the effect of oat-bran
concentrate (n8), oat extracts with b-glucans (n16), oat fibre
from oat husks/hulls (n7), oat gum (n2), avenanthramide-
enriched mixtures (n1) and fermented oat products (n1)
were excluded. The exclusion of each article was agreed by
two reviewers.
Data extraction
Data were extracted by one reviewer into pre-prepared tables
and a 10 % random sample of the data extraction was checked
and agreed by a second reviewer. The data extracted included
the country of study, participant characteristics (number, sex,
Articles from reference lists
(n 11)
Relevant articles
(n 38)
Potential articles
(n 244)
Excluded on full text
Full text not in English
Not an intervention
Intervention not oats
OAT abbreviation
Conference abstract
Effect of oats not clear
Outcomes not relevant
Not whole-grain oat
Response to exercise
Intervention less than 7 d
(n 217)
n 5
n 16
n 10
n 1
n 7
n 28
n 40
n 67
n 35
n 8
Duplicate articles
(n 520)
Potential articles
(n 654)
Ovid Medline (R)
(n 424)
Embase Classic + Embase
(n 521)
Cochrane Central Register of
Controlled Trials (n 229)
Excluded on title/abstract
Children
Animals
Other cereal
(Non-) oat cell carcinoma
OAT abbreviation
Other
(n 410)
n 41
n 3
n 29
n 94
n 141
n 102
Combined databases
(n 1174)
Fig. 1. Flow diagram of article selection.
Oats and bowel disease S33
British Journal of Nutrition
age and health status), intervention characteristics (length,
design and diet), variables adjusted for in the analysis and
relevant outcomes. The primary outcomes of interest included
characteristics of coeliac disease and UC; risk markers for
colorectal cancer; stool weight, transit time and frequency;
and faecal SCFA.
Quality of reporting
The Jadad scale for reporting randomised controlled trials
(RCT)
(14)
was used with a slight modification to score the qual-
ity of reporting of each article. Each article received one point
(1) if randomisation of participants to treatment was men-
tioned, (2) if the method of randomisation was appropriate,
(3) if blinding of the researchers/lab technicians to the inter-
vention was mentioned, (4) if the method of blinding was
appropriate and (5) if the number of all patients who started
and completed the trial was clear, with reasons stated if
no data were given. One point was also deducted if either
the method of randomisation or blinding was considered
inappropriate. Possible scores could range from 0 to 5. Studies
were categorised as having a low or high quality of reporting
if the total score was between 0 and 2, or 3 and 5, respectively.
We also recorded the presence or absence of a sample size or
power calculation for each article.
Reporting preferences
Studies were classified as RCT (1) if subjects were randomised
to treatments groups, (2) if there was an appropriate control
group and (3) if responses were compared between the oat
and control groups. For studies that showed a statistically sig-
nificant (P,0·05) effect of oats consumption, the percentage
change from baseline in the oat intervention group relative
to the control group was the preferred outcome of interest
to present. If this was not available in the article, it was calcu-
lated from the results given, and such values are indicated in
the tables.
Results
We identified thirty-eight articles
(13,15 – 51)
describing twenty-
nine studies that assessed the effect of oat consumption on
bowel disease (Fig. 1). Two studies were each carried out in
participants with a history of colorectal adenomas
(15,16)
(Table 2) or UC
(17,18)
(Table 3), eleven studies (described in
seventeen articles
(13,19 – 34)
) were carried out in participants
with coeliac disease (Table 4), and fourteen studies
(35 – 48)
were carried out in participants without a history of colorectal
adenomas, UC or coeliac disease (Table 5).
Colorectal cancer risk
Two studies
(15,16)
were carried out in participants with a
history of colorectal adenomas (Table 2). A 2-week oat-bran
intervention had no significant effect on putative risk
measures for colorectal cancer (colonic mucosal labelling
index, mucosal labelling pattern and micronuclei per crypt)
Table 2. Characteristics of studies in participants with a history of colorectal adenomas
Participants Intervention
Study Country nSex F (%) Age (years) Health RCT Design Length Diet(s)
Kashtan et al.
(15)
Canada 43 (oats) M and F 31 28–79 Healthy Yes Parallel 2 weeks Oat-bran or wheat-bran
supplementation
at 6·8g fibre/4814 kJ
(1000 kcal) (maximum
of 16·4g/d fibre)
46 (wheat) M and F 50 29–74 Post-polypectomy
or normal colon
Macrae et al.
(16)
Australia 20 M and F 45 36– 75 With $1 adenoma
removed at recent
colonoscopy
Yes Crossover 6 weeks 25 g unprocessed wheat
bran or 64 g unprocessed
oat bran or 38 g processed
wheat bran (all bran)
F, female; RCT, randomised controlled trials; M, male.
F. Thies et al.S34
British Journal of Nutrition
in post-polypectomy and non-polyp Canadian patients
(15)
.
Similarly, 64 g/d of oat-bran for 6 weeks had no significant
effect on measures of rectal epithelial cell proliferation
(number of crypts, number of labelled cells/crypt column,
number of cells/crypt column, total labelling index and
percentage of labelled cells within compartments) in twenty
Australian patients with recent adenomas
(16)
. Both articles
were categorised as having a low quality of reporting.
Ulcerative colitis
Two Swedish studies
(17,18)
assessed the effect of oat-bran con-
sumption in participants with UC (Table 3). Hallert et al.
(17)
found no signs or symptoms of colitis relapse in twenty-two
patients adding 60 g/d of oat bran to their daily diet for
12 weeks. In fact, those who reported any gastrointestinal
complaint at entry had a significant reduction in abdominal
pain and reflux by 24 and 55 %, respectively, after consuming
oat bran
(17)
. Zhang et al.
(18)
found that the addition of oat-bran
bread to the diet for 3 weeks in nine participants procoto-
colectomised for UC significantly increased the wet and dry
weights of ileostomy effluent by 73 and 88 %, respectively,
in comparison with wheat flour bread. The quality of report-
ing for both articles was considered low.
Coeliac disease
Table 4 shows the characteristics of the eleven studies carried
out in patients with coeliac disease (described in seventeen
articles
(13,19 – 34)
). Three studies were carried out in the
UK
(19,20,26)
, five in Finland
(13,21 – 23,25,27 – 30)
, and one each in
Norway
(24)
, Ireland
(31,32)
and Sweden
(33,34)
. The number of
subjects in each intervention group ranged from four to
thirty-five, and the interventions involved consuming between
34 and 100 g/d of oats for between 14 d to 5 years. The quality
of reporting for the seventeen articles
(13,19 – 34)
was considered
low (modified Jadad score between 0 and 2) for ten
articles
(13,19 – 25,31,34)
and high (modified Jadad score between
3 and 5) for seven articles
(26 – 30,32,33)
.
Analyses of intestinal biopsy specimens have mostly shown
either no change or a slight improvement in various measures
including ratios of surface to volume
(20)
and villous height
to crypt depth
(25,26,30)
, enterocyte height
(26,31,32)
, villous
atrophy
(13,21,23,27)
, villous architecture
(26,33)
, histomorphometric
index
(13,27)
, morphological damage
(31,32)
, mononuclear-cell
infiltration
(13,27)
, Marsh score
(24)
, mucosal inflammation
(21,23)
,
grade of inflammation
(33)
, mucosal human leucocyte antigen
DR (HLA-DR) expression
(25,29,32)
, enterocyte lactase
expression
(32)
, CD25 positive cells/1 mm
2(32)
, intercellular
adhesion molecule 1 (ICAM-1) (CD54) staining
(32)
and
lamina propria blood vessel size
(32)
. In the Norwegian
study
(24)
however, one patient was found to be intolerant to
oats and developed mucosal changes and dermatitis.
Intraepithelial lymphocyte counts were also reported to
have remained within normal limits
(26)
, or not changed signifi-
cantly in five studies
(25,28,29,31,32)
. While a Finnish study
(30)
found a slight but significant increase in CD3
þ
and gd intrae-
pithelial lymphocyte densities, the authors stated that the
Table 3. Characteristics of studies in participants with ulcerative colitis
Participants Intervention
Study Country nSex F (%) Age (years) Health RCT Design Length Diet(s)
Hallert et al.
(17)
Sweden 22 (oats) M and F 45 20 – 77 Ulcerative colitis No Parallel 12 weeks 60g/d oat bran to daily diet
v. no oat bran (control)10 (control) M and F 30 21– 64
Zhang et al.
(18)
Sweden 9 M and F 22 27– 67 Procotocolectomised for
ulcerative colitis With
ileostomies Good general health
Yes Crossover 3 weeks 272 g/d wheat flour bread
(187 g/d wheat flour) or
408 g/d oat-bran bread
(135 g/d oat bran)With ileostomies
Good general health
F, female; RCT, randomised controlled trials; M, male.
Oats and bowel disease S35
British Journal of Nutrition
Table 4. Characteristics of studies in participants with coeliac disease
Participants Intervention
Study Country nSex F (%) Age (years) Health RCT Design Length Diet(s)
Low quality of reporting (modified Jadad score 0–2)
Baker & Read
(19)
UK 12 M and F 33 5– 59 Coeliac disease No SC 14 –100 d 60 g/d uncontaminated oats
Dissanayake et al.
(20)
UK 4 –* – Coeliac disease No SC 4 weeks 40 – 60 g/d porridge oats
Kemppainen et al.
(21– 23)
Finland 31 M and F 58 16– 64 Coeliac disease No Cross-over 6 months 100 g/d kilned oats or
unkilned oats
Lundin et al.
(24)
Norway 19 M and F 89 Adults Coeliac disease No SC 12 weeks 50 g/d contaminant free oats
Reunala et al.
(25)
Finland 11 (oats) M and F 55 36– 61 Coeliac disease No Parallel 6 months 50 g/d porridge oats free of
gluten contamination or
home-baked bread (control)
11 (control) M and F 55 30 –67 DH
High quality of reporting (modified Jadad score 3 –5)
Hardman et al.
(26)
UK 10 M and F 30 44– 71 Coeliac disease No SC 12 weeks 50 – 70 g/d oats free of gluten
contaminationDH
Janatuinen et al.
(27,28)
Finland 26 IR (oats) M and F 65 48 (12)† Coeliac disease Yes Parallel 6– 12 months 50– 70 g/d oats or gluten-free
diet without oats (control)26 IR (control) M and F 65 42 (10)
19 ND (oats) M and F 63 42 (14)
21 ND (control) M and F 76 48 (11)
Janatuinen et al.
(13)
and
Kemppainen et al.
(29)
Finland 35 (oats) M and F 63 53 (12) Coeliac disease Yes Parallel 5 years 10–70 (mean 34) g/d rolled
oats and oat breakfast cereals
freely taken or no oats (control)
28 (control) M and F 64 52 (10) Follow-up study
(27,28)
Peraaho et al.
(30)
Finland 23 (oats) M and F 74 25– 69 Coeliac disease Yes Parallel 1 year 50 g/d oats-containing gluten-free
products or no oats16 (no oats) M and F 75 22 –65
Srinivasan et al.
(31)
and
Feighery et al.
(32)
Ireland 10 – Adults Coeliac disease No SC 12 weeks 50 g/d porridge oats (gluten-free)
Størsrud et al.
(33,34)
Sweden 15 M and F 60 22 – 71 Coeliac disease No SC 2 years 100 g/d uncontaminated
rolled oats
F, female; RCT, randomised controlled trials; M, male; SC, self-controlled; DH, dermatitis herpetiformis; IR, in remission; ND, newly diagnosed.
* Not available.
† Means and standard deviations (shown in parentheses).
F. Thies et al.S36
British Journal of Nutrition
Table 5. Characteristics of studies in participants without a history of colorectal adenomas, ulcerative colitis or coeliac disease
Participants Intervention
Study Country nSex F (%) Age (years) Health RCT Design Length Diet(s)
Low quality of reporting (modified Jadad score 0 – 2)
Abrahamsson et al.
(35)
Sweden 12 (oats) Women 20 –46 Healthy Yes Crossover 5 weeks 376g/d bread buns containing
oat bran or wheat bran
(20 g fibre)
12 (wheat)
Anderson et al.
(36)
USA 10 Men 34– 66 HC No Crossover 21 d 100 g/d oat bran after control diet
Hosig et al.
(37)
USA 9 (oats) Men 19 –28 Healthy No Parallel 28 d 100 g/d oat bran or 30 g/d
wheat bran9 (wheat)
Judd & Truswell
(38)
UK 10 M and F 40 24 –37 No SC 21 d 125 g/d rolled oats after
control diet
Kirby et al.
(39)
USA 8 Men 35 –62 88 % HC No Crossover $10 d 100g/d oat bran or no oat bran
Kretsch et al.
(40)
and
Calloway & Kretsch
(41)
USA 6 (83 % Caucasian
17 % African
American)
Men 23 –40 Healthy No Crossover 15 d Egg formula (control) alone or
with toasted or untoasted oat
bran (0·6 g/kg body weight)
Kristensen & Bugel
(42)
Denmark 24 M and F 22–30 Healthy No Crossover 2 weeks 102 g oat bran/10 MJ or no
oat bran
Marlett et al.
(43)
USA 9 Men 23·8 (2·2)* Healthy, NC No Crossover 28 d 100 g/d oat bran or low-fibre diet
Noakes et al.
(44)
Australia 23 M and F 43 44– 64 Hypertriglyceridaemic Yes Crossover 4 weeks 121/87 g/d (M/F) oat bran or
low-amylose starch diet
Sturtzel & Elmadfa
(45)
,
Sturtzel et al.
(46,47)
Austria 15 (oats) 57–98 Multiple chronic
diseases
No Parallel 12 weeks 7 –8 g/d oat bran or habitual
diet (control)
15 (control) Laxative use
Valle-Jones
(48)
UK 50 M and F 64 60–80 Constipation No SC 12 weeks Two oat-bran biscuits
per d (Lejfibre)
High quality of reporting (modified Jadad score 3 – 5)
Arffmann et al.
(49)
Denmark 6 Men 22– 26 Healthy Yes Crossover 2 weeks 18 g/d oat bran or 18 g/d
breadcrumbs
Kestin et al.
(50)
Australia 24 Men 29 –61 HC Yes Crossover 4 weeks 95 g/d oat bran, 35g/d wheat
bran or 60 g/d rice- bran
Payler et al.
(51)
UK 10 Caucasian M and F 80 31 – 64 Slow intestinal transit Yes Crossover 3 weeks 20 g/d oatmeal or wheat bran
for 1 week then 40 g/d
for 2 weeks
F, female; RCT, randomised controlled trials; M, male; HC, hypercholesterolaemic; SC, self-controlled; NC, normocholesterolaemic.
* Mean and standard deviation (shown in parentheses).
Oats and bowel disease S37
British Journal of Nutrition
density was relatively mild when compared with patients
treated for coeliac disease in general.
Evidence from nine studies suggests that oats consump-
tion has little impact on serum levels of antibodies
to gliadin
(13,24 – 26,28,31 – 33)
, reticulin
(13,26,28)
or endomy-
sium
(13,21 – 26,30 – 33)
following the consumption of oats.
The addition of oats to a gluten-free diet appears to have no
negative effects on nutritional status, as indicated by little
change in BMI
(13,22,27,33,34)
, weight
(22)
or blood concentrations
of vitamin A, D or E
(22)
; folate or vitamin B
12(20,27,30,33,34)
; Hb,
ferritin or Fe
(27,30,33,34)
;Ca
(22,27)
;Mg
(22)
; albumin
(27,33,34)
or
alkaline phosphatase
(33,34)
. However, Kemppainen et al.
(22)
found a significant reduction in serum vitamin B
12
after the
consumption of kilned or unkilned oats.
One study
(22)
found no significant change in serum total- or
HDL-cholesterol concentrations in response to the consump-
tion of kilned or unkilned oats. However, after 6 months of
consuming a diet with unkilned oats, serum TAG concen-
trations decreased significantly by 24 % but returned to
near-baseline level after a further 6 months using kilned oats.
There were two studies
(25,26)
of patients with dermatitis
herpetiformis. In a UK study
(26)
, dermal IgA showed no signifi-
cant changes following oat consumption and there were no
reports of pruritis or rash. In a Finnish study
(25)
, IgA fluor-
escence on the skin increased in one patient only, two
patients developed a transient rash and one patient withdrew
due to the appearance of a persistent but mild rash, in com-
parison with three of the control patients who developed a
transient rash and had IgA deposits on the skin. Both studies
concluded that patients with dermatitis herpetiformis can
include moderate amounts of oats in the diet and that the
rash in these patients is not activated by eating oats.
In patients with coeliac disease, the effect of oats on gastro-
intestinal symptoms was varied. Symptoms included diarrhoea
and flatulence
(19,24,30,33,34)
, nausea
(19)
, bloating or abdominal
distension
(22,24)
, constipation
(30)
and anorexia and irritabil-
ity
(19)
. In some studies, patients remained symptom free, had
no adverse effects or there was no significant difference in
symptoms compared with the control group
(20,21,26,28,31,32)
.
Some studies showed improvements in symptoms, including
a reduction in indigestion
(30)
, improved bowel function
(34)
and an increase in the percentage of patients without symp-
toms from 50 % at baseline to 67% at 24 months
(33)
.
Reasons for withdrawal of patients with coeliac disease
from studies included gastrointestinal symptoms such as dis-
tension and flatulence
(13,28,30,33,34)
or pain
(24,30)
, vomiting
(23)
,
rash
(13)
and worsening of itching without signs of dermatitis
(in patients with dermatitis herpetiformis)
(27,28)
. In one
study
(13)
, the main reason given for withdrawing was uncer-
tainty of the safety of oats.
Other studies in participants without coeliac disease
reported increased flatulence
(35)
or no significant side
effects
(17,39,48)
associated with oats consumption.
Bowel function
Table 5 describes the fourteen studies (seventeen
articles
(35 – 51)
) that were carried out in participants without a
history of colorectal adenomas, UC or coeliac disease. Five
studies were carried out in the USA
(36,37,39 – 41,43)
, three in the
UK
(38,48,51)
, two in Denmark
(42,49)
, two in Australia
(44,50)
and
one each in Austria
(45 – 47)
and Sweden
(35)
. The number of sub-
jects in each intervention group ranged from six to fifty (with
only one study containing more than twenty-four subjects per
group) and the interventions lasted between at least 10 d and
12 weeks. The quality of reporting for the seventeen articles
was considered low for fourteen articles
(35 – 48)
, and high for
three articles
(49 – 51)
.
Oat consumption significantly increased wet and dry stool
weight in six out of nine studies (from 15 to 88 % increase)
and five out of six studies (from 15 to 101 % increase), respect-
ively (Table 6). Stool frequency did not change significantly in
five studies, improved in two studies and reduced in one study
relative to wheat-bran and rice-bran interventions. Transit time
decreased significantly by 17 % in only one
(39)
out of four
studies (Table 6). In addition, an American study
(40)
found
no effect of toasted or untoasted oat bran on retention time
of a dye marker (the period until it was no longer detectable).
Two studies in older participants with constipation have
both found beneficial effects of oat bran. A UK study
(48)
found that consumption of two oat-bran biscuits per d in indi-
viduals aged 60– 80 years improved bowel frequency
(Table 6), increased the proportion of participants with
normal stool consistency (16 – 84 %) and reduced the pro-
portion who had pain on defecation (20– 6 %). In addition,
an Austrian study
(45 – 47)
of frail nursing home residents
found that adding 7–8 g/d of oat bran to the diet significantly
reduced laxative use by 59 % in comparison with a non-signifi-
cant increase of 8 % in the control group. However, a study
(35)
in younger women reported no significant effect of oat bran
on stool consistency.
Faecal SCFA
There is a lack of evidence to support an effect of oats on
faecal SCFA excretion
(15,17,44)
. Kashtan et al.
(15)
found no
change in faecal SCFA or butyric acid after a 2-week oat-bran
RCT in participants with a history of colorectal adenomas.
Similarly, Hallert et al.
(17)
found no significant change in the
faecal excretion of a variety of SCFA or in the sum of SCFA
after their 12-week oat-bran intervention in participants with
UC, although butyric acid was increased significantly by
36 % at the fourth week and hepatonic acid was increased
significantly by 100 % at the eighth week. While Noakes
et al.
(44)
’s RCT found no change in the faecal excretion of
acetate or propionate, the excretion of butyrate was signifi-
cantly lower after 4 weeks of oat bran compared with a
high-amylose diet.
Statistical analysis
Only one
(42)
of the thirty-eight
(13,15 – 51)
articles described
adjusting for any variables (body weight, sex, baseline
values and period) in their analyses. Only two articles
described carrying out a sample size or power calculation.
F. Thies et al.S38
British Journal of Nutrition
Quality of reporting
For the thirty-eight articles
(13,15 – 51)
reviewed, the total modi-
fied Jadad score ranged from 0 (13 % of articles) to 4 (3% of
articles). The most common total score was 1 (32 %), followed
by 2 (29 %) and 3 (24 %). Nineteen articles (50 %) mentioned
randomisation of participants to an intervention group, and
the method of randomisation was reported and judged to be
appropriate for one article. Blinding of researchers to treat-
ment was mentioned in ten articles (26 %), and the method
of blinding was reported and judged to be appropriate in
seven of these. The number of participants who started and
completed the trial was clearly described, with the reason
being stated if no data, for twenty-eight articles (74 %).
Discussion
Strength and limitations of review
To our knowledge, the present study is the first systematic
review to assess the effects of long-term interventions with
oat products on a range of bowel functions/diseases/risk
markers. Of the thirty-eight articles
(13,15 – 51)
included in the
present review, eleven were identified from the reference
lists rather than from the database searches, highlighting the
importance of using multiple sources to identify relevant
articles. It is possible that the database search strategy
missed these studies because the journals were not covered
by the databases, or the terms used to identify intervention
studies alone were too restrictive. It is likely that publication
bias had an impact on the findings of the present review:
articles showing significant results are more likely to be sub-
mitted, published or published more quickly than studies
without such characteristics, and articles published in
languages other than English were excluded.
The present review is limited by the small number of studies
in participants with a history of colorectal adenomas or UC,
and the lack of studies identified in patients with CD. The
majority of studies had a small sample size and many studies
lacked an appropriate control group. The studies were rela-
tively heterogeneous in terms of the intervention diet
(amount and type of oat product), the control diet used and
the clinical markers reported for each condition. However, it
is difficult to pinpoint specific markers for each disorder,
considering the variability and complexity of symptoms and
biomarkers associated with bowel disease. Therefore, future
studies are required to assess the effect of different types of
oat products and their dose–response effect for various
bowel conditions, and such studies need to be adequately
powered, contain an appropriate control group and target pri-
mary outcome measures that can be compared across studies.
Colorectal cancer
The hypothesis linking fibre intake with colorectal cancer risk
was originally proposed by Burkitt
(52)
nearly 40 years ago.
Increased stool bulk and dilution of carcinogens in the colonic
lumen, reduced transit time and bacterial fermentation of fibre
to SCFA have been suggested as possible mechanisms of
Table 6. Effect of oat consumption on stool weight, frequency and transit time
Comparison Wet weight Dry weight Frequency Transit time Reference
Low quality of reporting (modified Jadad score 0 – 2)
Oat bran v. wheat bran (20 g/d fibre) – * – NS – Abrahamsson et al.
(35)
100 g/d oat bran v. control diet 43 % "56 % "– – Anderson et al.
(36)
100 g/d oat bran v. 30 g/d wheat bran NS NS NS NS Hosig et al.
(37)
125 g/d rolled oats v. control diet NS 15 % "NS 17 %† #Judd & Truswell
(38)
100 g/d oat bran v. no oat bran 15 %† "22 %† "– – Kirby et al.
(39)
Toasted oat bran v. control 65 %† "92 %† "NS NS Kretsch et al.
(40)
and Calloway & Kretsch
(41)
Untoasted oat bran v. control 88 %† "101 %† "NS NS
102 g oat bran/10 MJ v. no oat bran 45 % "70 % "– – Kristensen & Bugel
(42)
100 g/d oat bran v. low-fibre diet 44 %† "– – – Marlett et al.
(43)
121/87 g/d (M/F) oat bran v. low-amylose starch diet NS – 13 % "– Noakes et al.
(44)
7 –8 g/d oat bran v. habitual diet (control) – – NS – Sturtzel et al.
(46)
Two oat bran biscuits per d v. baseline – – No stool: 12 v. 64 %† – Valle-Jones
(48)
High quality of reporting (modified Jadad score 3 – 5)
18 g/d oat bran v. 18 g/d breadcrumbs 34 %† "– – – Arffmann et al.
(49)
95 g/d oat bran v. 35 g/d wheat bran – – 9 %† #– Kestin et al.
(50)
95 g/d oat bran v. 60 g/d rice bran 12 %† #
40 g/d oatmeal v. 40 g/d wheat bran or baseline – – – NS Payler et al.
(51)
M, male; f, female.
* Not reported.
† Percentage change calculated from information in original article.
Oats and bowel disease S39
British Journal of Nutrition
action
(53)
. Recent evidence highlighted the protective role of
whole-grain foods against colorectal cancer
(3,54)
. However,
despite the observational epidemiological evidence, few inter-
vention studies have been conducted in order to confirm the
association between whole-grain consumption and decreased
risk of colorectal cancer, as well as to assess the effects of
specific whole-grain foods. As described in the present
review, only two intervention studies with oats have been car-
ried out in participants with a history of colorectal adenomas,
and neither showed any significant effects on putative and
indirect risk factors for colorectal cancer. Furthermore, these
studies included only a small number of patients and had
a short follow-up. It is therefore impossible to draw any
conclusion with regard to the results obtained, and further
research including comprehensive and well-designed trials is
warranted.
Inflammatory bowel disease
Our literature search identified only two long-term interven-
tion studies with oats in patients with UC and none in patients
with CD. However, only one of these studies was relevant
in terms of improvement in the patients’ conditions, with
a reduction in relapse and decrease in abdominal pain and
reflux
(17)
.
Experiments with animal models suggested that a loss of tol-
erance to gut microbiota could be central to the pathogenesis
of IBD
(55)
; however, this has not been confirmed in patients
with IBD. Antibiotic therapy has no beneficial effect on UC
while it provides some clinical benefits in luminal CD
(56)
.
Defects in innate or humoral and adaptive immune response
to host microbiota occur in CD
(57,58)
and UC
(59,60)
,
respectively. Drug therapy for IBD includes the use of various
anti-inflammatory drugs such as aminosalicylates (PPARg
agonist) or corticosteroids. However, probiotic therapy
seems effective in inducing and maintaining remission
in UC patients
(61,62)
, which underlines the potential benefit
of using the prebiotic properties of oats as an adjuvant to
probiotic/pharmaceutical treatment for UC patients.
Coeliac disease
Coeliac disease presents a wide spectrum of clinical manifes-
tations, characterised by diarrhoea, abdominal distension
and failure to thrive in young children
(63)
, while older children
and adolescents more often present atypical gastrointestinal
complaints including pain, vomiting, or constipation as well
as other symptoms such as arthritis, neurological symptoms,
anaemia or asymptomatic silent disease
(64)
. In adults, the
main feature of the disease is diarrhoea
(65)
, but anaemia
(66)
and osteoporosis
(67)
are also prominent. Other manifestations
include villous atrophy, dermatitis herpetiformis, IBS,
bloating, and chronic fatigue as well as various neurological
presentations
(68)
.
The results of the present review are in agreement with
Thompson’s review
(69)
of articles published between 1995
and 2003, and Haboubi et al.
(70)
’s systematic review of articles
published up to 2005, which show that including oats in the
diet of patients with coeliac disease has mostly no detrimental
effects on the intestinal mucosa morphology and inflam-
mation. Serum concentration of antibodies against gliadin
also remained unchanged after oat consumption. Further-
more, symptoms generated by dermatis hepetiformis were
not worsened after oat consumption. The results of the pre-
sent study suggest that the majority of patients with coeliac
disease can tolerate up to 100 g/d of uncontaminated oats.
Relieving the restrictions on oats for patients with coeliac
disease could increase the acceptability of, and adherence
to, a gluten-free diet.
However, it is often difficult to avoid the contamination of
oats by traces of other gluten-containing cereals such as
wheat cereals. Commercial oats may be processed in facilities
that also process gluten-containing cereals. Contamination can
also happen in the field, or during the transport of the grains,
so conventionally grown, and therefore the level of contami-
nation in processed oats can vary. It is therefore probably
not appropriate to suggest that oats can be safely consumed
by coeliac patients who are very sensitive to gluten. Some coe-
liac disease patients may also be intolerant to oats
(24,71)
, and
there is currently no accurate estimate of the prevalence of
oats intolerance in coeliac disease.
Bowel function
Dysfunctional bowel function is a common feature of many
intestinal disorders such as IBS and includes abdominal pain
relieved after defecation, changes in stool frequency/
consistency as well as flatulence and bloating
(72)
. Only a
limited number of studies examined the effects of oats on mar-
kers of bowel function. The majority of the studies described
in the present review showed no significant effect of oats on
stool frequency or transit time. However, oats or oat bran sig-
nificantly increased stool weight (dry and wet) and decreased
constipation, which would suggest that increasing oat con-
sumption could benefit people suffering from IBS. However,
these effects do not seem to be specific to oats when compari-
sons with wheat or rice bran are considered
(37,50,51)
.
Gut motility may be one of the mechanisms linking dietary
factors and physical activity with colorectal cancer risk
(52)
.
However, results of epidemiological studies are inconclu-
sive
(73 – 76)
, and appropriately powered, well-designed
RCT are required to properly assess the effects of oats on
bowel function. Considering bowel function as a marker for
colorectal cancer risk is currently inadequate considering the
discrepancy of results obtained from epidemiological studies.
SCFA
SCFA, such as butyrate, are the product of bacterial
fermentation of dietary fibre in the colon. Many studies
using cell culture and animal models have assessed the effects
of butyrate on colon cancer, with conflicting results
(77)
.
Butyrate has been shown to modulate cellular proliferation
(78)
,
apoptosis
(79,80)
and cell differentiation
(81)
. The few studies that
examined the effects of oat consumption on SCFA production
do not support a positive effect on SCFA. All studies used
F. Thies et al.S40
British Journal of Nutrition
faecal SCFA concentration as a surrogate marker for SCFA pro-
duction. However, such measurement does not represent the
actual epithelial exposure. Inter- and intra-individual SCFA
productions are also highly variable due to many confounders
such as recent dietary intake, colonic transit and hydration
status. Therefore, the interpretation of such data is greatly
limited.
Conclusion
Long-term dietary intake of oats or oat bran could present
some benefits for patients with IBS and UC. A protective
effect on colorectal adenoma and cancer is plausible but it
has not been convincingly shown. Relieving the restrictions
on oats for patients with coeliac disease could increase the
acceptability of, and adherence to, a gluten-free diet. How-
ever, further research including comprehensive and well-
designed trials is required to assess the efficacy of increased
oat consumption against bowel disorders.
Acknowledgements
The authors thank M. Mowett for sourcing the majority
of the articles. F. T. reviewed articles for inclusion, and drafted
the paper. L. F. M. carried out the literature search, extracted
the data and contributed to writing the paper; P. B.
and P. K.-E. contributed to writing the paper.
F. T., P. K.-E. and P. B. received an honorarium from Quaker
Oats Company (a subsidiary of PepsiCo, Inc.) for attending
the workshop in May 2012 to discuss the content of the
supplement, and the University of Aberdeen received an
unrestricted grant from Quaker Oats Company. L. F. M. has
no conflict of interest to report.
This paper was published as part of a supplement to British
Journal of Nutrition, publication of which was supported
by an unrestricted educational grant from Quaker Oats Co.
(a subsidiary of PepsiCo Inc.). The papers included in this
supplement were invited by the Guest Editor and have
undergone the standard journal formal review process. They
may be cited.
The Guest Editor to this supplement is Roger Clemens. The
Guest Editor declares no conflict of interest.
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