Review for 10.1186/s12876-021-01688-7 (2021)

Reviewer’s report
Title: 
Association of meat consumption with NAFLD risk and liver-related
biochemical indexes in older Chinese: a cross-sectional study
Version: 
0 
Date: 
13 Sep 2020
Reviewer's report:
In this study the authors aimed to explore the association between specific meet
subtypes consumption and the risk of NAFLD. They showed an increased risk of
NAFLD development derived from the overconsumption of red meat as well as
identified a positive correlation with serum levels of GGT, ALT, AST, TG and
negative correlation with HDL-C.
In this study it is possible to identify strength points like the sample size and the
detailed statistical analysis. However, some other concerns regarding the
scientific background surrounding the rationale of the study and the
methodologic approach exist.
Minor revisions
1. Abstract: "High meats intake contributes to unhealthy status" please describe
better considering your topic.
2. Abstract: "liver related biomarkers", please define.
3. Abstract-Methods: in this section it was not inserted a methods description.
Please change it.
4. Abstract: please insert the p values for all the mentioned evaluations
5. Keywords: meat consumption
6. Introduction: "Furthermore, liver-related clinical parameters such as 
γ
-
glutamyl transferase (GGT), aspartate aminotransferase (AST) and alanine
transaminase (ALT) were closely associated with NAFLD [21]. Elevated GGT,
AST ALT and were the markers underlying liver diseases such as NAFLD [22]."
Please modify the sentences. Even if there were indicated the sources of this
knowledge by specific references, nowadays it is largely accepted that the
indicated parameters don't represent useful markers for the disease, in particular
considering NAFLD in general and not NASH. Moreover AST, ALT and GGT
are not "clinical" but biochemical parameters.
7. Methods: "(D) Individuals who did not answer more than 25 food-related
items on the questionnaire." You excluded them from the analysis, not from the
enrollment, right? Please clarify. 
8. Results: please indicate the evaluated variables (where it is possible) in mg/dl,
not mmol/L
Major revision
1. What is the reason why the authors decided to enroll patients older than 45? It
would have been interesting to analyze the data of younger people also in order
to stratify the risk of meat overconsumption-NAFLD development among
different age ranges. This assumption is sustained by the analysis of the scientific
literature on this topic that identified in the young population an increasing
prevalence of NAFLD.
2. A study design flowchart is needed
3. In the inclusion/exclusion criteria: it was not mentioned the use of medication
that could potentially interfere with the showed results, as well as patients with
thyroids disturbances.
4. So, in order to evaluate the presence of NAFLD it was performed only an
abdominal ultrasonography examination. As not so sensible technique the
authors certainly considered the possibility of "some false negative patients".
Moreover, they didn't classify the patients in accordance to the severity of the
steatosis (CAP, MRI, FLI, etc). I think it is necessary to discuss these points in
the discussion section-study limitations.
5. Methods: the nutritional assessment was based on Semi-quantitative food
frequency questionnaire. The authors didn't assess completely dietary behavior
in terms of macro and micronutrients intake with a dedicate software
(WinFood® or something similar). That certainly could affect severely the
results of the study, due to the influence of some other dietary components on
the specified main endpoint.
6. Statistical analysis: 
- "Nonparametric Kruskal-Wallis test and Chi-Square test were performed for
comparisons between groups" what groups? Until this paragraph the authors
didn't mention a group stratification
- What is the reason for the application of non-parametric test? Did the authors
perform any assessment for normality (Kolgoromov-Smirnov or similar)?
- Confounding variables: medication
7. It is not clear the reason why the authors decided to assess some biochemical
variables and didn't use any strategy for the steatosis severity assessment.
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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