The global food system contributes significantly to greenhouse gas (GHG) emissions, accounting for approximately one-third of the total. This contribution is disproportionately influenced by dietary choices, with high-consumption groups, particularly those with diets rich in animal products, generating substantially more emissions. This disparity is observed both within and between countries, with wealthier populations generally having larger carbon footprints. Simultaneously, a considerable portion of the global population suffers from hunger and malnutrition, highlighting the complex interplay between food security, health, and environmental sustainability. Efficiency gains in food production haven't offset the increase in emissions driven by consumption patterns, necessitating a shift towards sustainable dietary choices to mitigate climate change. The study focuses on analyzing GHG emissions from diets, quantifying the unequal distribution of these emissions across various population groups, and assessing the potential emission reductions achievable through widespread adoption of the EAT-Lancet planetary health diet, a dietary framework designed to promote both human health and environmental sustainability.

Existing research demonstrates the significant environmental impact of food systems, particularly regarding GHG emissions and the critical need to reduce food-related emissions to achieve climate goals. Studies have explored the unequal distribution of energy consumption and carbon emissions across income groups within and between nations. Several studies have examined income- or expenditure-specific food-related emissions within individual countries, but a comprehensive global assessment considering specific products and population groups was lacking. Research also indicates that shifting to healthier diets, aligned with the UN's Sustainable Development Goals, offers a promising pathway to simultaneously address hunger, improve health, and mitigate emissions. The EAT-Lancet planetary health diet has emerged as a key option, aiming to reconcile healthy diets with planetary boundaries. While prior studies have estimated changes in country-specific environmental impacts (GHG emissions and water consumption) of adopting the planetary health diet, a detailed analysis of the varying contributions of diverse population groups has been limited.

This study utilized a consumption-based approach to quantify GHG emissions associated with diets in 2019. The analysis involved detailed household expenditure data, linked to a global consumption-based emissions inventory of 140 food products categorized into 13 food categories. The data encompassed 139 countries, representing 95% of the global population, and were structured into 201 expenditure groups based on per capita total expenditure, as derived from the World Bank Global Consumption Database (WBGCD). This allowed for analysis of emission inequalities across income groups. Food loss and waste during household consumption were subtracted from national food supplies to obtain dietary intake. A scenario modeling the transition to the EAT-Lancet planetary health diet was constructed to estimate potential emission changes. The GHG footprint, expressed as the dietary emissions per individual over a year, was used. Emission inequality was measured using the GHG footprint Gini (GF-Gini) coefficient. Logarithmic regression was used to analyze the relationship between the GF-Gini coefficients and per capita GDP. Uncertainty analysis employing a Monte Carlo approach was used to address uncertainty in activity data, emission factors, and various parameters. The study acknowledged limitations related to data availability, such as the use of regional household food loss and waste factors and the assumption of constant purchasing prices across expenditure groups. Missing data for some major food-consuming countries were addressed by using expenditure shares from similar countries.

Total global dietary emissions in 2019 reached 11.4 GtCO2e. China and India were the largest contributors. The highest country-average per capita footprints were observed in Bolivia and Luxembourg, while Haiti and Yemen had the lowest. Animal-based products accounted for 52% of global dietary emissions, while plant-based products comprised 48%, despite the latter providing 87% of dietary calories. Red meat, grains, and dairy products were the main emission sources. Regional disparities in emission contributions were substantial, with Australia, the United States, and Rest of East Asia having high proportions of emissions from animal-based products, while Indonesia, Rest of Southeast Asia, and Sub-Saharan Africa had higher emissions from plant-based products. Significant differences in per capita GHG footprints were found within countries, with richer populations generally having larger footprints related to animal-based products. The GF-Gini coefficient revealed that emission inequality tended to decrease with increasing per capita GDP, being highest in low-income countries, especially in Sub-Saharan Africa. Adopting the planetary health diet could potentially reduce global dietary emissions by 17%, with overconsuming populations saving 32.4% of emissions, offsetting increases from underconsuming populations. The largest emission reductions would stem from decreased red meat and grain consumption. However, increased consumption of legumes and nuts, added fats, and vegetables and fruits would partly offset these reductions. The reduction in per capita footprints would be most significant in wealthy consumer groups in high-income countries, while poor groups in many countries would experience an increase.

The findings highlight the significant contribution of dietary choices to GHG emissions and the substantial inequality in emission distribution across countries and income groups. The study's results demonstrate the potential of widespread dietary shifts, aligned with the EAT-Lancet planetary health diet, for reducing emissions. While the planetary health diet offers dual benefits by addressing both undernutrition and climate change, the implementation requires region- and country-specific policies, acknowledging the varying dietary patterns and affordability of different food items. Reducing overconsumption of emission-intensive products in affluent countries is crucial, while in low-income countries, enhancing agricultural production efficiency and affordability of healthier diets are critical. The study underscores the need for policy interventions that incentivize sustainable dietary changes while addressing potential negative impacts on vulnerable groups, such as agricultural households in low-income countries. The significant changes in food demand projected under the planetary health diet indicate the need for careful planning and adaptation within the global agri-food system to accommodate altered production patterns and market dynamics.

This study demonstrates substantial inequality in dietary emissions globally, with high-income countries exhibiting higher emissions per capita but lower inequality, and low-income countries demonstrating lower emissions but higher inequality. Widespread adoption of the EAT-Lancet planetary health diet offers significant potential for GHG emission reductions, but requires tailored policies considering regional and national contexts and economic disparities. Future research should focus on the feasibility and social implications of achieving such dietary shifts, incorporating dynamic modeling and comprehensive assessment of the socio-economic impacts across various sectors.

The study's limitations include data availability constraints, such as regional food loss and waste factors and assumptions regarding constant purchasing prices across expenditure groups. Missing data for some countries required imputation. Furthermore, the scenario modeling assumed unchanged food production technology and trade patterns. The study did not consider dynamic impacts on prices or income distribution as a result of changing food demand.