Review for 10.1186/s12876-024-03392-8 (2024)

Title: Association between plant-based dietary index and disease severity in patients with
ulcerative colitis: A cross-sectional study
Version: 0 Date: 26 Apr 2024
Reviewer's report:
Report
I read with great interest the manuscript entitled " Assessment of the association between plant-
based dietary index and disease severity in patients with ulcerative colitis: A cross-sectional
study" by Nikniaz et al. They concluded that a plant-based diet is associated with lower disease
severity score in ulcerative colitis patients, although, the study was cross-sectional, and therefore
could not report on causal relationships. However, the results are interesting from a clinical point
of view in diet recommendations – a topic very important to many patients with IBD.
Firstly, I have some general comments:
Page and line numbers would have been helpful, at least for the review process. I therefore added
these on each page (with line numbers starting over again on each page).
The authors should also consider English proofreading of the manuscript by a native English
speaker.
I would encourage the authors to make more of their results in the discussion by making a clearer
argument about what they think they mean.
My further comments to the different sections in the manuscript:
INTRODUCTION
Page 3, line 8:
I suggest also citing reference 9 and 10 when referring to previous studies (the references 4-8)
that “showed that various dietary components could affect intestinal inflammation, microbiota,
immunity, and mucosal barrier function (4-8).”
Page 3, line 16-17:
“In other inflammatory conditions, the adverse association between a PBD and C-reactive
protein has been shown [13].” Do you mean “inverse” association?
Page 3, lines 21-24:
Suggest moving the information about the PDI to the methods section.
Page 4, line 5:
Suggest including a brief explanation of Mayo score, for example “and the Mayo Score for
disease activity (reference) in patients with UC.”
METHODS
Page 4
Line 9:
Please provide the time of recruitment (exact date).
Insert “were” after “patients” in the sentence: “The patients included in the present study (…)”
Lines 7-10:
How was UC defined? Please provide the diagnosis code used and write where the diagnostic
information came from (e.g. electronic patient record or similar).
Line 12:
Insert “they” after etc.
Lines 13-14:
Please expand the abbreviation “PASS software”, for example: The PASS Sample Size and
Power Software (ref.) was used…
Please explain in a little more detail, but briefly, what you mean about “the result” of the similar
study.
Lines 18-21:
Please provide a more detailed description of the variables – how there were defined. Educational
level (primary, secondary, tertiary or other categories?); marital status (married, single?);
smoking (previous, never, current smoker?); disease duration (in days?); which treatments and
supplements? Etc.
Lines 21-22:
Suggest rewording to: “The Mayo score was used for determination of disease severity and is
described elsewhere (reference).”
Page 5, lines 5-6:
Suggest deleting these lines as I do not think it is necessary to explain the calculation of BMI.
You already said in the previous lines that the nutritionist used standard protocols.
General: Consider including a flowchart of the inclusion/exclusion of participants.
Statistical analysis:
Page 6, line 5:
Were the data for all variables normally distributed? If not, you should use medians.
Lines 9-12:
“The result of regression was adjusted for age, sex, smoking, drinking alcoholic beverages,
disease duration, comorbidities, prednisolone use, dietary supplements use, and BMI.”
Suggest rewording: The model was adjusted for the potential confounders: (variables).
Furthermore, please make sure that there is consistency between the covariates described in this
section and the covariates described previously. For example, comorbidities are not mentioned
in the previous section (page 4) describing the included covariates. Also, be consistent with
the wording throughout the manuscript – use for example “covariates” when speaking of the
included variables not being the exposure or the outcome variables.
RESULTS
Page 6, line 17:
Suggest rewording “The information regarding general characteristics and disease-related
evidence” to “The demographic and disease-related characteristics of study participants across
tertiles of..” and copy this to the title of the Table 1 also.
Lines 18-19:
Sugggest rewording to: “Although participants were similar regarding most of the demographic
and disease-related variables across tertiles of PDI, hPDI, and uPDI, there were significant
differences in… “
Medical treatment also shows significant differences across PDI tertiles. These are not
mentioned in the description of the results of Table 1, although interesting as medical treatment
could be regarded as a surrogate measure of disease severity.
Line 23:
Suggest rewording to: “Table 2 presents the risk difference (or relative risk?) estimates of the
linear regression analysis of the association between PDI score and disease severity”.
The effect measure in this study (risk difference (RD)?) should be provided in the abstract, the
method section and the results section, including the table. Suggest writing the results in the
following way: (RD: -0.21 (95% CI: -1.89 ; -0.17)).
DISCUSSION:
Page 7, Line 12-13:
Suggest deleting or rewording of the sentence.
Page 7, Line 14:
A positive association means that when one variable is increased, the value of another variable
increases. This is not the case in this study. When PDI increases, the severity of UC decreases.
Please rephrase.  Also see page 8, line 2.
Page 8, line 3:
Please expand the abbreviation “SFA”.
Page 8, Lines 8-9:
The explanation in line 8-9 should be further elaborated. Which effect does the inclusion of fish
and seafood on the index have on the association?
Page 8, Lines 11-14:
English proofreading/the text needs revision.
Page 8, Line 15:
Strengths
Line 20:
Which biases are the authors referring to? Please elaborate.
CONCLUSION
I recommend not using the wording “negative association” or “positive association”, as it may
lead to misunderstandings. Rather describe the association using more words – a higher PDI
was associated with lower disease severity score.