Introduction: Ensuring healthy diets within planetary boundaries is essential. However, current instruments measuring adherence to the EAT-Lancet planetary health diet are unsuitable for large-scale surveys. Simplified tools assessing consumption frequency can improve response rates, lower costs, and facilitate administration. This study aimed to develop a practical and concise index for evaluating relative adherence to the EAT-Lancet diet across large-scale multi-country surveys. Methods: First, the EAT-Lancet Consumption Frequency Index (ELFI) was developed using a brief food propensity questionnaire of 14 food groups representing the planetary health diet from the FEAST survey, which encompassed 27 European countries (n = 27,417). Subsequently, ELFI was further validated using 24-hour dietary recalls from the INCA3 survey (n = 1,645), correlating it with the valid EAT-Lancet Index (ELI), which evaluates absolute adherence, as well as with food group consumption, measures of nutritional health (nutrient adequacy and diet quality), and environmental impact. Analyses included assessment of reliability, structural validity, concurrent validity, and nomological validity. Results: ELFI showed strong reliability (alpha > 0.80) and factor analysis revealed a two-factor solution: foods to encourage and foods to balance and to limit. Confirmatory factor analysis demonstrated that ELFI is structurally valid. Concurrent validity was confirmed as it was associated with sex, age, education, income, household size, physical activity and smoking habit (p < 0.05). ELFI correlated with ELI (0.44, p < 0.0001) and food group consumptions. Regarding nomological validity, the ELFI subscores for foods to encourage and foods to balance and to limit were associated with better nutritional health (β = 0.62 and 0.23, respectively; p < 0.0001) and a lower environmental impact (β = -0.16 and -0.36, respectively; p < 0.0001). Conclusion: ELFI approach represents a valuable and easy-to-implement index for evaluating relative adherence to sustainable and healthy diets in large-scale multi-country studies.

The authors have declared no competing interest.

https://assets-eu.researchsquare.com/files/rs-4464994/v1/22975163-cc5e-4a43-8bb0-aec22c1585bf.pdf?c=1723545447

This study is part of the FEAST (Food systems that support transitions to healthy and sustainable diets) project funded by the European Union's Horizon Europe research and innovation program under grant agreement number 101060536 and by Innovate UK under grant number 10041509. Swiss participant in FEAST is supported by the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number 22.00156. More details in https://www.feast2030.eu/.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Ethical approval for the FEAST survey was granted by the conjoined Ethics Committee of Scuola Superiore SantAnna and Scuola Normale Superiore (Resolution No. 29/2023, and following amendments). The INCA3 study adhered to the Declaration of Helsinki and received approval from the French Data Protection Authority (Decision DR 2013-228) and the Advisory Committee on Information Processing in Health Research (Opinion 13.055).

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Data from the Third French Individual and National Food Consumption Survey (INCA3) in available on the data.gouv.fr platform at: https://www.data.gouv.fr/fr/datasets/donnees-de-consommations-et-habitudes-alimentaires-de-letude-inca-3/. Data on the environmental impacts of foods consumed in France is available on the agribalyse.ademe.fr platform. FEAST anonymous survey data will be made available coherently with the FEAST Data management Plan: https://feast2030.eu/sites/default/files/feast/resources_files/2024/FEAST_WP1_DMP-PlanDel1.2_D_20240528_V2.pdf.

https://www.data.gouv.fr/fr/datasets/donnees-de-consommations-et-habitudes-alimentaires-de-letude-inca-3/