Dietary changes and uneven sanitation systems widen urban-rural health environment efficiency disparity

Diets have synergistic effects on human health and environmental pollution, comprehensively revealing their impact mechanisms is crucial for promoting health-and environment-friendly diets. This study proposes a Health-Environment Efficiency (HEE) indicator, defined as the ratio of health benefits to diet-related reactive nitrogen (Nr) emissions, to reveal the environmental cost of supporting human health through diets in urban and rural China from 1980 to 2022. Although dietary changes improved health benefits in both areas, per capita Nr emissions increased by 17.9 % in urban areas and 105.1 % in rural areas, leading to divergent HEE trends. From 1980 to 2003, increased animal-based food consumption caused additional Nr pollution, offsetting health benefits and causing a continuous decline in HEE. During 2004-2022, healthier diets and upgraded sanitation systems improved urban HEE, widening the urban-rural disparity eightfold. Urban sanitation system has become the primary driver of Nr reduction, while rural dietary changes still caused a 0.2 Tg increase in Nr emissions. Projections to 2050 under shared socioeconomic pathways suggest that integrating dietary transitions with treatment upgrades can effectively balance health and environmental goals, narrowing the urban-rural HEE disparity by 48.4 %.