Review for 10.1186/s12876-024-03515-1 (2024)

Title: The Relationship between Food Components and Constipation: A Cross-Sectional Study
Version: 1 Date: 24 Sep 2024
Reviewer's report:
I thank the editor for inviting me to review this manuscript and I have several comments.
1. Figure 1 lists the exclusion criteria for this study; however, the authors used ellipses when
mentioning the missing data on demographics, BMI, and Bristol type. The inclusion and
exclusion criteria are a serious and important process, and the authors should provide all the
exclusion conditions.
2. In the Methods section of the article, there are two instances (Study Population and
Data Collection, Analyses and Statistical Methods) where inclusion and exclusion criteria are
mentioned, but the descriptions are not consistent. For example, in the Analyses and Statistical
Methods section, it states that 8,634 participants were excluded due to missing covariate data.
However, from the Study Population and Data Collection section and Figure 1, it is evident that
many were excluded because they were under 20 years of age.
3. Why did the authors use two samples? After applying the inclusion and exclusion criteria,
an analysis sample of 1,696 participants was generated; however, the second paragraph of the
Analyses and Statistical Methods section mentions an analysis sample of 1,903 participants.
Additionally, Table 1 analyzes the sample of 1,903 participants. Why did the authors conduct
the analysis this way? Furthermore, the abstract states that all the analysis samples consist of
1,903 participants.
4. The authors stated that they used the MEC weights in this study. Does this mean that the entire
study utilized these MEC weights? I noticed that both Table 1 and Table 2 used sample weights
for the analysis. Did the logistic regression analysis in Table 3 also use weights? If weights were
used, it should not be MEC weights; instead, dietary weights, namely wtdrd1 or wtdrd2, should
have been employed. Additionally, since Table 2 also involves dietary variables, dietary weights
should have been used there as well.
5. The statistical methods used to calculate the p-values in Tables 1 and 2 should be clearly
described.
6. The presentation of results in Table 3 is inconsistent with the statistical methods described
in the Analyses and Statistical Methods section. The section mentions that stepwise regression
analysis was used for both single-factor and multi-factor analyses. If this is the case, the results
for single-factor analysis with p > 0.05 should not be displayed. Additionally, what is the
difference between the "multivariate analysis" and the "final analysis" mentioned in Table 3? Is
the method for including variables in the multivariate analysis a enter method?
7. Figure 2 should indicate the p-values for the analyses described by the authors in the Results
section, and the statistical methods used to calculate the p-valuesshould be clearly described in
the Analyses and Statistical Methods section.
8. The authors state that "Although p < 0.05 for added sugar, the OR value is equal to 1.157;
therefore, added sugar does not affect the occurrence of constipation." However, the results in
Table 3 show that the final analysis indicates an OR of 1.01 for added sugar, with a p-value
of 0.037.
9. Table 3 should indicate the reference group; for example, the odds ratio (OR) can be
represented as 1 or labeled as "reference," rather than leaving it blank.
10. The threshold for vegetable intake of 2.93 (cups/d) needs to be clearly explained by the
authors. Additionally, the method used to determine the categorized values for vegetable intake,
specifically the range of 0-0.77 (cups/d), should also be described in detail.
11. The authors stated that they used multiplicative interaction to test the significance of
interaction, and that the forest plot showed the odds ratio (OR) value and its 95% confidence
interval (CI). However, these results and the forest plot are not found in the article.
12. The authors' description of added sugar is indeed confusing. According to the results in
Table 3, when added sugar is analyzed as a continuous variable, its odds ratio (OR) is 1.01, and
the p-value is less than 0.05. This suggests that the lower limit of the 95% confidence interval
(CI) should also be greater than 1. Such results cannot support the authors' assertion that "added
sugar does not affect the occurrence of constipation." Furthermore, the discussion section is also
worth reconsidering.
13. The authors' segmentation of vegetable intake levels is also quite confusing. Firstly, there is
no explanation provided for why these specific segments were chosen or the basis for grouping
them. Additionally, in the abstract, there is no mention of vegetable intake in the methods or
results sections, yet a description of 2.93 cups per day appears in the conclusion. Furthermore,
the results section of the main text only refers to the two thresholds of 2.93 (cups/d) and 0-0.77
(cups/d), while the discussion section mentions that "segmented analysis shows that the OR
value of vegetable intake between 2.2-2.93 cups/d is over 1." Overall, the authors' segmented
analysis of vegetable intake is unclear.