Diet item details: reporting checklist for human feeding studies measuring the dietary metabolome—consensus results from an online Delphi study

Nutritional metabolomics is an emerging objective dietary biomarker method to help characterise dietary intake. Our recent scoping review identified gaps and inconsistencies in both design features and level of detail of reported dietary intervention methods in human feeding studies measuring the metabolome (1) and our cross-over feeding study protocol details dietary information for identification of metabolites that characterise ‘healthy’ and ‘unhealthy’ (typical) Australian diets (2) . The current study aimed to gain consensus on core diet-related item details (DID) and recommendations for reporting DIDs to inform development of a reporting checklist. The aim of this checklist is to guide researchers on reporting dietary information within human feeding studies measuring the dietary metabolome. A two-stage online Delphi was conducted encompassing 5 survey rounds (February–July 2024). This study is approved by the University of Newcastle’s Human Research Ethics Committee (HREC; H-2023-0405). Sixty-seven experts were invited across expertise in clinical trial design, feeding study intervention implementation, metabolomics, and/or human biospecimen analyses. Twenty-eight DIDs categorised across five domains underwent consensus development. Stage 1 (2 rounds) gained consensus on a core set of DIDs, including phrasing. Stage 2 (3 rounds) gained consensus on standard reporting recommendations for each DID and acceptance of the final reporting guideline. The research team convened after every round to discuss consensus-driven results. Experts resided from Australia, New Zealand, United States, United Kingdom, Sweden, Israel, Italy and Denmark. Twenty-five completed stage 1 and n = 22 completed stage 2. After stage 1, two DIDs merged and two new DIDs were identified, totalling 29 core DIDs. At the end of stage 2, round 2, based on expert feedback, all items were organised to determine differing degrees of reporting in the methods section of publications, with additional recommendations collated for other sections, including supplementary files. The reporting guideline (DID-METAB Checklist) was generated and accepted by the expert working group in round 3, with all experts agreeing that relevant journals should include the checklist as a suggested reporting tool for relevant studies or used alongside existing reporting tools. The Delphi process gained consensus on a core set of DIDs, and consolidated expert views on the level of detail required when reporting DIDs in research. The Delphi process generated the reporting guideline (DID-METAB Checklist) which can be implemented independently or as an extension to existing guidelines such as CONSORT (at item 5) or SPIRIT (at item 11) to improve reproducibility and comparability of feeding studies. Endorsement by scientific societies and journals will be key for the dissemination strategy and optimising the utility of the tool to strengthen the evidence base of nutritional metabolomics. The DID-METAB Checklist will be a key tool to advance reporting of diet-related methodologies in metabolomics for both personalised and precision nutrition interventions in clinical practice.