Background: Unhealthy diets, the rise of non-communicable diseases, and the declining health of the planet are highly intertwined, where food production and consumption are major drivers of increases in greenhouse gas (GHG) emissions, substantial land use, (LU) and adverse health outcomes such as cancer and mortality.

Methods: In the European Prospective Investigation into Cancer and Nutrition (EPIC), a multi-centre prospective cohort study (n=443,991), we estimated associations between dietary contributions to GHG emissions and LU and all-cause and cause-specific mortality and incident cancers using Cox proportional-hazard regression models. Co-benefits, encompassing the potential effects of alternative diets on all-cause mortality and cancer and potential reduction in GHG emissions and LU, were estimated using counterfactual attributable fraction (AF) intervention models, simulating potential effects from dietary shifts based on the EAT-Lancet reference diet.

Findings: There was an association between levels of dietary-based GHG emissions and LU and all-cause mortality, with a Hazard Ratio and 95% Confidence Interval (CI) of 1.13 (1.10, 1.16) and 1.18 (95% CI: 1.15, 1.21), respectively, comparing the fourth quartile to the first (HRQ4 vs Q1). Similar associations were observed for cause-specific mortality. There were also associations between overall cancer rates and GHG emissions (HRQ4 vs Q1: 1.11, 95% CI: 1.09, 1.14) and LU (HRQ4 vs Q1: 1.13, 95% CI: 1.10, 1.15); however, estimates differed by cancer type. Through counterfactual AF modelling of shifts in diets, we find that between 19 to 63% of deaths and 10 to 39% of cancers could be prevented, over a 20-year risk period, from adhering to different scores of the EAT-Lancet reference diet. Additionally, switching from a lower score of the EAT-Lancet reference diet to a higher score could reduce food-associated GHG and LU levels by 50% and 62%, respectively.

Interpretation: Our results support shifts in diets that could lead to co-benefits, minimizing dietary related GHG emissions and LU, to reduce environmental footprints, aiding in climate change mitigation, and improving population health.