This study examines the health-environment efficiency of diets from 1990 to 2011 across 195 countries. It defines health-environment efficiency as the ratio of health benefits to four key environmental impacts: greenhouse gas emissions, scarcity-weighted water withdrawal, acidifying emissions, and eutrophying emissions. The results show that this efficiency follows a nonlinear trend along the Socio-Demographic Index (SDI) gradient, which represents different levels of socio-economic development. Initially, efficiency increases as food supply improves and child and maternal malnutrition decreases. However, it then decreases due to increased environmental impacts from a shift to animal-based diets. Finally, in some developed countries, efficiency slowly increases as they transition to healthier diets. The study highlights the complex relationship between dietary patterns, health outcomes, and environmental impacts. While improving diets can reduce health risks and environmental pressures, it can also lead to trade-offs, such as increased greenhouse gas emissions from dairy product consumption. The findings suggest that dietary transitions can lead to win-win solutions or conflicts between health and environmental goals. The study emphasizes the need for policies that promote sustainable food consumption patterns to achieve Sustainable Development Goals, including zero hunger, good health and wellbeing, responsible consumption and production, climate action, life below water, and life on land. The study also discusses the challenges and opportunities for policymakers in different stages of dietary transition. It provides insights into how environmental and health outcomes change with socio-economic development and highlights the importance of integrating health and environmental considerations in food policy. The health-environment efficiency indicator developed in this study can be used to guide efforts towards dietary sustainability at different development levels. The study underscores the need for further research to improve the accuracy and applicability of the indicator, as well as to address the limitations of the current data and methods.This study examines the health-environment efficiency of diets from 1990 to 2011 across 195 countries. It defines health-environment efficiency as the ratio of health benefits to four key environmental impacts: greenhouse gas emissions, scarcity-weighted water withdrawal, acidifying emissions, and eutrophying emissions. The results show that this efficiency follows a nonlinear trend along the Socio-Demographic Index (SDI) gradient, which represents different levels of socio-economic development. Initially, efficiency increases as food supply improves and child and maternal malnutrition decreases. However, it then decreases due to increased environmental impacts from a shift to animal-based diets. Finally, in some developed countries, efficiency slowly increases as they transition to healthier diets. The study highlights the complex relationship between dietary patterns, health outcomes, and environmental impacts. While improving diets can reduce health risks and environmental pressures, it can also lead to trade-offs, such as increased greenhouse gas emissions from dairy product consumption. The findings suggest that dietary transitions can lead to win-win solutions or conflicts between health and environmental goals. The study emphasizes the need for policies that promote sustainable food consumption patterns to achieve Sustainable Development Goals, including zero hunger, good health and wellbeing, responsible consumption and production, climate action, life below water, and life on land. The study also discusses the challenges and opportunities for policymakers in different stages of dietary transition. It provides insights into how environmental and health outcomes change with socio-economic development and highlights the importance of integrating health and environmental considerations in food policy. The health-environment efficiency indicator developed in this study can be used to guide efforts towards dietary sustainability at different development levels. The study underscores the need for further research to improve the accuracy and applicability of the indicator, as well as to address the limitations of the current data and methods.