Synergies Between Food Biodiversity, Processing Levels, and the Eat-lancet Diet for Nutrient Adequacy and Environmental Sustainability: a multiobjective optimization using the European Prospective Investigation into Cancer and Nutrition cohort

Background: Diets have become increasingly monotonous and high in ultraprocessed foods (UPFs), contributing to poor health outcomes and environmental degradation. Although sustainable diets, food biodiversity, and food processing levels have each been linked to nutritional and environmental outcomes, their combined impact has not been assessed. Objectives: This study aims to examine whether food biodiversity, intakes of UPFs, and adherence to the EAT-Lancet diet can simultaneously optimize nutrient adequacy while reducing environmental impacts. Methods: Using data from 368,733 adults in the European Prospective Investigation into Cancer and Nutrition, we assessed associations and interactions between dietary species richness (DSR) (disaggregated into DSR _Plant and DSR _Animal), food processing levels (Nova categories; % g/d), and adherence to EAT-Lancet recommendations [healthy reference diet (HRD) score; 0–140 points] with the Probability of Adequate Nutrient Intake Diet (PANDiet) score, dietary greenhouse gas emissions (GHGe; kg CO ₂-eq/d), and land use (m ²/d). Regression models subsequently informed multiobjective optimization to identify optimal dietary patterns balancing nutritional and environmental outcomes. Results: Compared with observed diets, optimal diets showed a mean HRD score increase of 13.91 (95% confidence interval: 13.89, 13.93) points; DSR _Plant increased by mean of 1.36 (1.35, 1.37) species, and a mean substitution of 12.44 (12.40, 12.49) percentage points of UPFs with unprocessed or minimally processed foods. Correspondingly, the mean PANDiet score increased by 4.12 (4.10, 4.14) percentage points, whereas GHGe and land use reduced by 1.07 (1.05, 1.09) kg CO ₂-eq/d and 1.43 (1.41, 1.45) m ²/d, respectively. Conclusions: Diets that adhere to the EAT-Lancet diet, are more biodiverse, and prioritize unprocessed and minimally processed foods over UPFs, have the potential to synergistically enhance nutrient adequacy while minimizing environmental impacts. These findings suggest that moderate improvements across multiple dietary dimensions simultaneously can achieve meaningful gains in both nutritional adequacy and environmental sustainability.