40:60: The optimal ratio between animal and plant-based proteins for health and environment

Summary

There is currently little agreement on the optimal ratio of animal-sourced (ASP) versus plant-sourced proteins (PSP) in sustainable human diets. We deployed a biophysical optimization model to find the optimal ASP:PSP ratio at current and recommended protein intake levels for the EU28 countries. Results show that the lowest environmental impact for both land use and greenhouse gas emissions is achieved at a recommended protein intake of 46 g protein/cap/day with an ASP:PSP ratio of 40:60 (18 g ASP/cap/day). At current protein intake (82 g protein/cap/day), the optimal ASP:PSP ratio for land use ranges evenly between 22:78 and 60:40 (18 and 49 g ASP/cap/day) while for greenhouse gas emissions the optimal ASP:PSP ratio is at 40:60 (18 g ASP/cap/day). Diets containing less than 18 g ASP/cap/day show micronutrient inadequacies, leading to increases in both land use and greenhouse gas emissions.