Review for 10.1186/s12876-025-04021-8 (2025)

Title: Association between Dietary Index of Gut Microbiota and abnormal bowel symptoms in
U.S. adults: a cross-sectional study from NHANES 2007–2010
Version: 1 Date: 13 Apr 2025
Reviewer's report:
Major Comments
1. Causality and Study Design
The cross-sectional design limits the ability to infer causality between DI-GM and bowel
symptoms. While this is acknowledged, the discussion should emphasize this limitation more
explicitly and recommend longitudinal or interventional studies to establish causal relationships.
2. Validation of DI-GM
The manuscript references a 2024 study (Ref. 14) for DI-GM validation but does not provide
sufficient details on how this index correlates with actual gut microbiota biomarkers (e.g.,
sequencing data, SCFA levels). Clarify whether Ref. 14 is published or under review and include
key validation metrics (e.g., correlation coefficients) in the methods or supplementary materials.
3. Rationale for DI-GM Components
The selection of 14 specific foods/nutrients for DI-GM lacks justification. Provide evidence or
references supporting why these components were chosen over others (e.g., mechanistic links
to microbiota diversity). Were other foods (e.g., prebiotics, polyphenol-rich foods) considered?
4. Subgroup Analysis Interpretation
Subgroup analyses reveal interactions (e.g., race, recreational activity), but the discussion does
not explore potential explanations for these findings. Hypothesize why these subgroups might
exhibit differential associations (e.g., dietary habits, genetic factors) to enrich the interpretation.
5. Chronicity of Bowel Symptoms
The definition of "chronic" constipation/diarrhea is unclear. Specify the duration criteria (e.g.,
Rome IV criteria) used in the NHANES Bowel Health Questionnaire to ensure consistency with
clinical standards.
Minor Comments
1. Abbreviations
Define all abbreviations upon first use (e.g., DI-GM, NHANES, RCS) for clarity.
2. Formatting  Issues
- Tables 1 and 2 are duplicated at the end of the manuscript; remove duplicates.
- Ensure consistent formatting of p-values (e.g., *P* = 0.002 vs. *P* < 0.001).
3. Statistical Reporting
Specify the R packages used for weighted logistic regression and RCS analyses (e.g., `survey`,
`rms`).
4. Figure Citations
Figures 1–4 are referenced but not included in the manuscript. Ensure figures are provided with
clear captions and legends (e.g., explain the inflection point at DI-GM = 5 in Figure 4).
5. Grammar and Syntax
- Revise awkward phrasing (e.g., "prevent the disease and prevent the disease from changing"
# "prevent disease progression").
- Correct typographical errors (e.g., "Depresssion" in Table 1).
6. Reference Consistency
Ensure in-text citations match the reference list (e.g., Ref. 28 is cited as "Kiecolt-Glaser et al.,
2019" but listed under "Marriage and gut feelings").
7. Dietary Recall Limitations
Expand on the limitations of 24-hour dietary recalls (e.g., day-to-day variability, underreporting)
and how these might affect DI-GM scoring.
8. Ethics Statement
Clarify whether secondary analysis of NHANES data required separate ethics approval or relied
solely on the original NHANES IRB approval.
9. Repetitive Content
The introduction and discussion sections repeat background information about gut microbiota.
Condense redundant passages to improve readability.