Review for 10.1186/s12876-015-0393-0 (2015)

Reviewer ’s report  
 
Title: Perceived food intolerance and irritable bowel syndrome in a population 3 years after a  
giardiasis -outbreak: a historical cohort study  
 
Version: 0 Date: 20 Sep 2015  
 
Reviewer: Per G Farup  
 
Reviewer's report:  
 
The paper compares perceived food intolerance in subjects three years after an infection with 
Giardia lamblia with a control group. The authors have published several papers from the same 
dataset, such as chronic fatigue three  and six years after the infection, and the relation between 
fatigue, IBS, and overactive bladder six years after the infection. There is some overlap between 
the papers, but not more than acceptable.  
The topic of the paper is of interest, and the paper is  in large well written and presented.  
 
Major concerns:  
One of the aims was to study the effect of high and low FODMAP foods on perceived food 
intolerance, and the conclusion in the abstract was that "high FODMAP foods were not more 
important than low FODM AP foods in causing………". The formulation "more important" is not 
scientifically correct, and the paper does not allow any conclusions about "cause" but only about 
associations.  
It is unacceptable not to report the results of one of the three main aims of the study. On page 9 - 
lines 32 -35 the authors write "data not shown". It is probably correct that there were no 
differences between high and low FODMAP foods, but the data (the results) have to be reported 
with confidence intervals in the same way as the other results.  
The wording is confusing. "Perceived food intolerance", "abdominal symptoms", "self -reported 
abdominal symptoms" and "IBS" have been used inconsequently. There ar e three types of 
abdominal symptoms with some overlap: "Abdominal symptoms related to intake of food 
(perceived food intolerance)", "IBS" and "abdominal symptoms not associated with intake of 
food and not fulfilling the Rome III criteria for IBS". E.g the last sentence of the abstract, what 
are abdominal symptoms? Is it "perceived food intolerance", "all abdominal symptoms with or 
without relation to food", or "IBS with or without food intolerance". How have the authors 
classified patients with abdominal co mplaints not related to food, and not qualified for the IBS 
diagnosis? The scoring of the Rome III criteria always reveals symptoms that do not qualify for 
the diagnosis of IBS.  
 
 
Minor concerns:  
Page 5 - lines 50 -55 refer to "categories" and "conventional  categories". Please explain the 
categories.  
Page 6 - line 42. Age was categorized in 20 years groups. Page 7 lines 36 -37 report the results of 
mean age as 36.1 and 32.9. Does it give any meaning when age was categorized in 20 years' 
groups?  
Page 8 line 12. It is a bit confusing that question 2 is aim 3.  
Page 12 lines 1 -3. The authors raise the hypothesis that the pathogenesis of IBS and food 
intolerance is identical. My belief is that the pathogenesis differs because a substantial proportion 
of the subj ects has a food intolerance and not IBS and vice versa. The Giardia infection might 
activate several immunological pathways. Of course, the authors present their hypothesis and not 
mine.  
In all, the discussion is vague and introduces new results and disc ussion about fibre and gluten. 
The discussion could be more to the point.  
Are the methods appropriate and well described?  
If not, please specify what is required in your comments to the authors.  
 
Yes 
 
Does the work include the necessary controls?  
If not, please specify which controls are required in your comments to the authors.  
 
Yes 
 
Are the conclusions drawn  adequately supported by the data shown?  
If not, please explain in your comments to the authors.  
 
No 
 
Are you able to assess any statistics in the manuscript or would you recommend an  
additional statistical review?  
If an additional statistical review is reco mmended, please specify what aspects require further  
assessment in your comments to the editors.  
 
I am able to assess the statistics  
 
Quality of written English  
Please indicate the quality of language in the manuscript:  
 
Acceptable  
 
Declaration of competing in terests  
Please complete a declaration of competing interests, considering the following questions:  
 
1. Have you in the past five years received reimbursements, fees, funding, or salary from an 
organisation that may in any way gain or lose financially from the publication of this 
manuscript, either now or in the future?  
 
2. Do you hold any stocks or shares in an organisation that may in any way gain or lose 
financially from the publication of this manuscript, either now or in the future?  
 
3. Do you hold or are you currentl y applying for any patents relating to the content of the 
manuscript?  
 
4. Have you received reimbursements, fees, funding, or salary from an organization that 
holds or has applied for patents relating to the content of the manuscript?  
 
5. Do you have any other financial competing interests?  
 
6. Do you have any non -financial competing interests in relation to this paper?  
 
If you can answer no to all of the above, write 'I declare that I have no competing interests' 
below. If your rep ly is yes to any, please give details below.  
 
I declare that I have no competing interests.  
 
I agree to the open peer review policy of the journal. I understand that my name will be included 
on my report to the authors and, if the manuscript is accepted for pu blication, my named report 
including any attachments I upload will be posted on the website along with the authors' 
responses. I agree for my report to be made available under an Open Access Creative Commons 
CC-BY license ( http://creativecommons.org/licens es/by/4.0/ ).  I understand that any comments 
which I do not wish to be included in my named report can be included as confidential comments 
to the editors, which will not be published.  
 
I agree to the open peer review policy of the journal