Association Between Self-Reported Dietary Intake Questionnaires and Objective Measures in an Inpatient Cross-Sectional Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I recommend using the STROBE checklist to support and qualify the report.

 

It would be important to explain what an "inpatient study" is (assumptions, objectives, implications). I think that, being a more general journal, greater contextualization is needed.

 

Two points that seem important to me are: (1) what is the external validity of this research? This needs to be discussed and presented in more depth, and (2) what are the suggested paths for future studies?

 

Is there any possibility of using this evidence in practical decision-making? I recommend discussing this.

Author Response

Reviewer 1

We thank the reviewer for their time and thoughtful suggestions, which have greatly improved the quality of our manuscript. Below, we detail how we have addressed each of these comments.

• I recommend using the STROBE checklist to support and qualify the report.
• See attached strobe checklist and amendments made to the paper to align more closely with the checklist. 
• It would be important to explain what an "inpatient study" is (assumptions, objectives, implications). I think that, being a more general journal, greater contextualization is needed. Two points that seem important to me are: (1) what is the external validity of this research? This needs to be discussed and presented in more depth, and (2) what are the suggested paths for future studies?
• We felt that the explanation of “inpatient study” aligned with your point about external validity and addressed them together. See page 10, lines 297-299. To address the comment on future studies see page 11 lines 325-334. 
• Is there any possibility of using this evidence in practical decision-making? I recommend discussing this.
• While we find this suggestion interesting, we ultimately feel it is outside the scope of this paper. We find our results are more applicable to informing lab-based/inpatient research settings and less so in the healthcare system as a whole. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors, 

Thank you for the opportunity to review the manuscript examining the concordance between self-reported dietary assessment and objective measures of intake in an inpatient research-unit setting. The study addresses a fundamental issue in nutritional research, namely the limitations of dietary questionnaires and their susceptibility to reporting error. A particular strength is that the Authors juxtapose three distinct self-report perspectives: declared intake frequency, food preference, and product selection for the experimental paradigm. An additional asset is the use of a vending-machine paradigm, which enables a quantitative, objective record of intake as well as an analysis of the energy contributions of specific food groups. The study considers six product groups defined by fat content and the predominant macronutrient type, which facilitates interpretation in terms of dietary patterns. The results indicate that associations between questionnaire ratings and actual intake are generally weak, which is consistent with prior reports on the limited validity of self-reported dietary measures. An interesting and potentially novel element is the observation of sex differences for low-fat product groups, where significant associations appear more frequently in men than in women. Such a signal may be relevant for interpreting population studies in which measurement errors can be systematic and dependent on participant characteristics. In this sense, the work adds value by linking the classic question of self-report error with a concrete, controlled measurement of eating behavior.

At the same time, in its current form, the interpretation of the findings requires greater caution and several methodological clarifications. First, please explicitly discuss the implications of selecting 40 vending-machine products based on ratings within a predefined range, as this may restrict variability and attenuate correlations. Second, please consider the impact of the very long recruitment period on the stability of the results, since 1999–2023 encompasses substantial changes in product availability and composition. Please also extend the analysis with an element addressing multiple testing, or clearly specify which tests are primary and which are exploratory. Next, please consider adding at least one complementary index of agreement beyond correlation, such as classification into tertiles/quartiles or a prediction-error measure for PctGrp. Please strengthen the discussion of generalizability, as an inpatient setting and the vending-machine paradigm may not reflect free-living eating behavior. Please also clarify how PctGrp was calculated and briefly explain how potential leftovers/waste and product weighing were handled. The supplementary materials are useful; however, please clarify whether the classification of products into macronutrient-based groups was updated over time or remained constant. Overall, the study has publication potential after revision, as it combines a robust objective measure with the question of the validity of tools commonly used in nutritional epidemiology. Please address the above suggestions point by point in your response to the reviewer and indicate where changes have been made in the manuscript.

Best regards,

The reviewer.

Author Response

Reviewer 2

We thank the reviewer for their time and thoughtful suggestions, which have greatly improved the quality of our manuscript. Below, we detail how we have addressed each of these comments.

Thank you for the opportunity to review the manuscript examining the concordance between self-reported dietary assessment and objective measures of intake in an inpatient research-unit setting. The study addresses a fundamental issue in nutritional research, namely the limitations of dietary questionnaires and their susceptibility to reporting error. A particular strength is that the Authors juxtapose three distinct self-report perspectives: declared intake frequency, food preference, and product selection for the experimental paradigm. An additional asset is the use of a vending-machine paradigm, which enables a quantitative, objective record of intake as well as an analysis of the energy contributions of specific food groups. The study considers six product groups defined by fat content and the predominant macronutrient type, which facilitates interpretation in terms of dietary patterns. The results indicate that associations between questionnaire ratings and actual intake are generally weak, which is consistent with prior reports on the limited validity of self-reported dietary measures. An interesting and potentially novel element is the observation of sex differences for low-fat product groups, where significant associations appear more frequently in men than in women. Such a signal may be relevant for interpreting population studies in which measurement errors can be systematic and dependent on participant characteristics. In this sense, the work adds value by linking the classic question of self-report error with a concrete, controlled measurement of eating behavior.

At the same time, in its current form, the interpretation of the findings requires greater caution and several methodological clarifications. 

• First, please explicitly discuss the implications of selecting 40 vending-machine products based on ratings within a predefined range, as this may restrict variability and attenuate correlations. 
• See adjustments on line 113 on page 3. 
• Second, please consider the impact of the very long recruitment period on the stability of the results, since 1999–2023 encompasses substantial changes in product availability and composition. 
• This is an interesting point and was also raised by another reviewer. We have previously published the secular trends in dietary intake from this same cohort and have included a new paragraph in the discussion on that, see page 10, lines 279-291. 
• Please also extend the analysis with an element addressing multiple testing, or clearly specify which tests are primary and which are exploratory. 
• We have improved upon language in the introduction (page 2 line 71) and in the methods (page 4 lines 163 and 167) to clarify the primary and exploratory aims.
• Next, please consider adding at least one complementary index of agreement beyond correlation, such as classification into tertiles/quartiles or a prediction-error measure for PctGrp.
• We thank the reviewer for this suggestion. The primary objective of this analysis was to evaluate continuous agreement, rather than categorical classification. Accordingly, we report multiple complementary continuous metrics (correlations, partial correlations, R2, and regression coefficients), which together characterize both the strength and direction of agreement between measures. Categorization into tertiles or quartiles would require introducing arbitrary cutpoints and would reduce the information content of the continuous outcome, without materially altering the interpretation of the results. For these reasons, we did not include additional categorical agreement analyses in the current study. 
• Please strengthen the discussion of generalizability, as an inpatient setting and the vending-machine paradigm may not reflect free-living eating behavior. 
• Thank you for identifying our oversight in not acknowledging the generalizability of our work. We have included more language on the inpatient setting impact on generalizability (page 10 lines 297-299) and we direct you to lines 299-301 for a discussion of the vending machine paradigm impact on generalizability. 
• Please also clarify how PctGrp was calculated and briefly explain how potential leftovers/waste and product weighing were handled. 
• A discussion on how PctGrp intake was calculated is briefly mentioned in the abstract (page 1 lines 20-21) and more thoroughly in the methods (page 4 lines 140-145). 
• For an explanation of the food waste processing, see lines 137-139 on page 4. 
• The supplementary materials are useful; however, please clarify whether the classification of products into macronutrient-based groups was updated over time or remained constant. 
• See addition of clarifying language on line 120 page 3. 

Overall, the study has publication potential after revision, as it combines a robust objective measure with the question of the validity of tools commonly used in nutritional epidemiology. Please address the above suggestions point by point in your response to the reviewer and indicate where changes have been made in the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for inviting me to review this paper. This study analyzed the correlation between self-reported dietary questionnaires and objectively measured ad libitum intake. The study topic and methodology are interesting. Some comments are outlined below for the authors.

 

Title/Abstract

- The context of the study, such as the name of the country or study period, should be clarified in the title or abstract

- In the abstract, the number of participants included should be clarified.

- Also, in the abstract, the statistical method employed should be clarified

 

2. Materials and methods

2.1. Subjects and recruitment

- The number of participants included should be clarified in this section.

- Please provide the reference number of the IRB approval.

 

2.5. Covariates

- Was there any information on the SES? (e.g., education, income, or occupation)

 

4. Discussion

- I believe that the study findings have some implications for future research. The recommendations for research and/or policy implementation should be discussed.

- The study period is very long (>20 years!). The dietary practices among the population might have significantly changed during the study period. The limitations related to the long-term nature of this study should be discussed.

Author Response

We thank the reviewer for their time and thoughtful suggestions, which have greatly improved the quality of our manuscript. Below, we detail how we have addressed each of these comments.

Thank you for inviting me to review this paper. This study analyzed the correlation between self-reported dietary questionnaires and objectively measured ad libitum intake. The study topic and methodology are interesting. Some comments are outlined below for the authors.

• Title/Abstract
• The context of the study, such as the name of the country or study period, should be clarified in the title or abstract
• In the abstract, the number of participants included should be clarified.
• Also, in the abstract, the statistical method employed should be clarified 
• Thank you for identifying these points that needed additional clarity. Please see adjustments on page 1 line 16 and 21-23. 
• Materials and methods
• 2.1. Subjects and recruitment
• The number of participants included should be clarified in this section.
• See page 2 lines 84-85 and 87-88 for clarification. 
• Please provide the reference number of the IRB approval.
• The original IRB approval date was 04/07/1999. The IRB number is OH99DKN019. 
• 2.5. Covariates
• Was there any information on the SES? (e.g., education, income, or occupation)
• For current studies, it is now in our standard protocol to collect SES information. However, it was not collected at the start of this study in 1993,  and thus did not report it in this analysis, as we didn’t have the information for many participants. 
• Discussion
• I believe that the study findings have some implications for future research. The recommendations for research and/or policy implementation should be discussed.
• We included a further discussion on the implications of this work that can be found in the conclusion, 11 lines 325-334. 
• The study period is very long (>20 years!). The dietary practices among the population might have significantly changed during the study period. The limitations related to the long-term nature of this study should be discussed.
• This is an interesting point and was brought up by another reviewer as well. See adjustments on page 10 lines 279-291. 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The new version is suitable for publication.

 

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

You introduced the significant improvements to your manuscript. I support its publication in its present form.

Best regards,

The reviewer.