Alignment between healthy and sustainable diets: comparing the 2019 and 2025 adaptations of the planetary health diet with the healthy eating index in the Bavarian population

Introduction Global food systems face the double challenge of ensuring human health and reducing environmental impacts. While the Healthy Eating Index (HEI) evaluates nutritional quality, the Planetary Health Diet (PHD) attempts to integrate ecological sustainability with healthy nutrition in its framework. This study assessed the agreement between the metric HEI-2015 (mHEI-2015) and two versions of a Planetary Health Diet Index (PHDI-2019 and its updated version PHDI-2025), as well as their associations with environmental indicators in a Bavarian population. Methods Cross-sectional data from the 3rd Bavarian Food Consumption Survey (BVS III, 2021–2023, n = 1,100, 18–75 years) were used to calculate mHEI-2015, PHDI-2019, and PHDI-2025, with the latter newly operationalized to reflect the updated 2025 PHD framework. Dietary greenhouse gas emissions (GHGE), land use (LU), and water footprint (WFP) were estimated. Statistical analyses included weighted kappa ( kw ) for agreement, correlation analyses, and survey-weighted regression models adjusted for sociodemographic factors. Results Mean mHEI-2015 was 51.3 out of 100 points, PHDI-2019 19.3 out of 42 points, and PHDI-2025 20.6 out of 45 points. Regression analyses showed that female participants, individuals with higher education, and residents of large cities (≥500,000 inhabitants) consistently scored higher across all indices (all p ≤ 0.047), whereas age was positively associated only with mHEI-2015 ( β = 1.9 per 10 years; p 0.001). Agreement between PHDI-2025 and PHDI-2019 was nearly perfect weighted kappa ( kw ) = 0.84, p 0.001. Agreement between PHDI-2025 and mHEI-2015 was modest ( kw = 0.38, 95% CI 0.35–0.42; r = 0.58; p 0.001). Across PHDI-2025 quintiles, higher adherence was associated with lower GHGE (−12.5%; p-trend 0.001) and LU (−28.6%; p-trend 0.001), while WFP was unchanged ( p-trend = 0.146). Across quintiles, the mHEI-2015 showed reduced LU (−16.3%; p-trend = 0.008), increased WFP (+16.7%; p-trend 0.001), and no GHGE change ( p-trend = 0.849). Conclusion Health- and sustainability-focused diet indices aligned only partially in the Bavarian population. Both PHDI versions, but not mHEI-2015, were associated with lower GHGE and LU. PHDI-2025 closely mirrored PHDI-2019, indicating refinement rather than redefinition.