Review for 10.1186/s12876-022-02301-1 (2022)

Reviewer’s report
Title: 
Effects of bowel preparation on intestinal bacterial associated urine and
faecal metabolites and the associated faecal microbiome.
Version: 
0 
Date: 
21 Jan 2022
Reviewer's report:
"PEER REVIEWER ASSESSMENTS: 
OBJECTIVE - Full research articles: is there a clear objective that addresses a
testable research question(s) (brief or other article types: is there a clear
objective)?
Yes - there is a clear objective
DESIGN - Is the current approach (including controls and analysis protocols)
appropriate for the objective?
No - there are minor issues
EXECUTION - Are the experiments and analyses performed with technical rigor
to allow confidence in the results?
Yes - experiments and analyses were performed appropriately
STATISTICS - Is the use of statistics in the manuscript appropriate?
Yes - appropriate statistical analyses have been used in the study
INTERPRETATION - Is the current interpretation/discussion of the results
reasonable and not overstated?
No - there are minor issues
OVERALL MANUSCRIPT POTENTIAL - Is the current version of this work
technically sound? If not, can revisions be made to make the work technically
sound?
Probably - with minor revisions
PEER REVIEWER COMMENTS: 
GENERAL COMMENTS: 
The authors present here a study on the effect of bowel cleansing with PEG
solutions on the microbiome and the metabonome, at different timepoints
regarding a colonoscopic procedure.
The researchers have done a good selection of the patients included, and
described the experimental design appropriately.
Besides, careful consideration was given in the discussion to the possible effects
of sample size and methodology on the results, and the conclusions of the study
were compared to other previous findings.
Overall, this manuscript is deemed suitable for publication with just some minor
changes that would add value for the readership.
REQUESTED REVISIONS: 
The authors recruited 11 patients to follow up before and after colonoscopy. Of
them, 9 were males. Although this is partly explained by the demography of
colon cancer and screening procedures, I would like the authors to comment on
the potential bias of this selection. For future studies, I would recommend to
include further patients so that this difference is not significant, eliminating thus
a possible bias on the results.
In relation to that question: are those 9 males the 9 samples showing intra-subject
clustering in the PCA over the 3 time points, or there is no influence of the
gender on this homogeneity?
ADDITIONAL REQUESTS/SUGGESTIONS: 
None."
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Is the study design appropriate to answer the research question (including the use
of appropriate controls), and are the conclusions supported by the evidence
presented?
No
Are the methods sufficiently described to allow the study to be repeated?
No
Is the use of statistics and treatment of uncertainties appropriate?
Yes
Is the presentation of the work clear?
Yes
Are the images in this manuscript (including electrophoretic gels and blots) free
from apparent manipulation?
Yes