Protein transition and circular food system transition are two proposed strategies for supporting food system sustainability. Here we model animal-sourced protein to plant-sourced protein ratios within a European circular food system, finding that maintaining the current animal–plant protein share while redesigning the system with circular principles resulted in the largest relative reduction of 44% in land use and 70% in greenhouse gas (GHG) emissions compared with the current food system. Shifting from a 60:40 to a 40:60 ratio of animal-sourced proteins to plant-sourced proteins yielded a 60% reduction in land use and an 81% GHG emission reduction, while supporting nutritionally adequate diets. Differences between current and recommended total protein intake did not substantially impact minimal land use and GHG emissions. Micronutrient inadequacies occurred with less than 18 g animal protein per capita per day. Redesigning the food system varied depending on whether land use or GHG emissions were reduced—highlighting the need for a food system approach when designing policies to enhance human and planetary health.

蛋白质转型和循环食品系统转型是支持粮食系统可持续性的两项拟议战略。在这里，我们对欧洲循环食品系统中动物源性蛋白质与植物源性蛋白质的比例进行了建模，结果发现，在保持当前动植物蛋白质份额的同时，按照循环原则重新设计系统，可以最大程度地相对减少 44% 的土地使用和与当前粮食系统相比，温室气体 (GHG) 排放量减少 70%。将动物源蛋白与植物源蛋白的比例从 60:40 转变为 40:60，土地使用量减少了 60%，温室气体排放量减少了 81%，同时支持营养充足的饮食。当前和推荐的总蛋白质摄入量之间的差异并未对最低土地利用和温室气体排放产生重大影响。人均每天动物蛋白摄入量低于 18 克，就会出现微量营养素不足的情况。重新设计粮食系统取决于土地使用或温室气体排放是否减少，这凸显了在设计促进人类和地球健康的政策时采用粮食系统方法的必要性。