One diet, many indices: heterogeneity in measuring adherence to the EAT-lancet planetary health diet

This study provides a systematic comparison of dietary indices developed to assess adherence to the EAT-Lancet planetary health diet. A literature search was conducted in PubMed and Scopus up to April 2026 following PRISMA guidelines. Studies were included if they described the construction of indices derived from the EAT-Lancet framework. Twenty-six indices were identified. Although all were based on the same reference model, substantial heterogeneity emerged in their operationalisation. Many indices were adaptations of a limited number of original frameworks, with differences in food group definition, number of components, and scoring procedures. Variability was also observed in scoring systems, ranging from binary to continuous approaches, and in the use of energy adjustment, including absolute, energy-standardised, or relative intake measures. Taken together, these differences may lead to non-equivalent measures of adherence. These results suggest that stronger methodological rigour and better standardisation are needed to improve comparability across studies evaluating sustainable dietary patterns.