Low-carbon diets can reduce global ecological and health costs

The global food system contributes significantly to greenhouse gas emissions, accounting for about one-third of the total. Mitigating climate change necessitates substantial emission reductions from this sector. Dietary change, particularly reducing consumption of animal-sourced foods (ASF), presents a significant mitigation opportunity. ASF production generates considerably more emissions per gram compared to plant-based foods (PBF). While the direct climate and environmental effects of dietary changes are relatively well-understood, the indirect economic repercussions (externalities) remain under-explored. These externalities, encompassing ecological and socio-economic costs not reflected in food prices, significantly impact human health and ecosystem quality. Previous studies on dietary externalities have been limited in scope, often focusing on specific countries, food types, or impact categories. This study addresses this gap by providing a holistic global assessment of the ecological and socio-economic costs of dietary changes.

Existing literature highlights the link between dietary shifts and climate change mitigation, demonstrating the potential of reducing ASF intake to yield significant climate benefits. Studies have also shown the positive impacts of such shifts on planetary stability and public health. However, a comprehensive quantification of the indirect cost repercussions of these dietary changes, particularly the externalities associated with food production, remains scarce. Previous research often lacks a global perspective or focuses on limited aspects like single countries, specific food types, or individual impact categories such as GHG emissions or nitrogen flows. This study aims to fill this gap by providing a more comprehensive and holistic analysis of the global externalities.

This study quantifies the indirect costs of nine global low-carbon dietary change strategies that progressively reduce ASF consumption. The methodology integrates life cycle impact assessment (LCIA) principles, Food and Agriculture Organization (FAO) Statistics Division Food Balance Sheets (FBS), and monetarization factors to assess the external costs of food supplies across 101 countries. The LCIA uses the ReCiPe2016 method to assess the environmental impacts of food production, considering categories such as terrestrial acidification, ecotoxicity, eutrophication, land use, global warming, ozone formation, water use, human toxicity, and particulate matter formation. These midpoint impacts are then linked to endpoint damage categories: damage to human health (measured in disability-adjusted life years, DALYs) and damage to ecosystem quality (measured in time-integrated species loss). DALYs and species loss are then monetarized using established factors to estimate the total external costs. Nine hypothetical dietary change scenarios were modeled, progressively reducing ASF and substituting them with PBF, insects, and processed plant-based alternatives. The scenarios include a baseline (2018 food supply pattern), the EAT-Lancet Commission's reference diet, and variations involving the progressive elimination of red meat, poultry, seafood, dairy, and eggs, along with partial substitutions with insect protein and processed plant-based alternatives. The impact of each scenario on both production-related and consumption-related health burdens was assessed. A comparative risk assessment approach was used to estimate changes in disease risk (coronary heart disease, stroke, cancer, type-II diabetes) associated with changes in food intake.

The study finds that the external costs of food production embedded in global diets in 2018 were substantial, amounting to US$14.0 trillion (US$5.9–32.8 trillion), equivalent to 17% (7–39%) of the world’s GDP. Approximately US$8.3 trillion was linked to human health burden and US$5.7 trillion to ecosystem quality decline. The hidden costs averaged US$1.94 (US$0.82–4.56) for every dollar of consumer expenditure. These hidden costs nearly tripled the true cost of the average global diet. Dietary shifts toward lower ASF consumption could generate significant savings. Eliminating red meat alone could save US$4.0 trillion (US$1.8–9.4 trillion) in externalities and 2.3 Gt CO₂e (2.0–2.8 Gt CO₂e) in GHG emissions. The complete exclusion of ASF (Vegan scenario) could deliver the largest savings—US$7.3 trillion (US$3.2–17.0 trillion) in externalities and abatement of approximately 4.5 Gt CO₂e (3.9–5.8 Gt CO₂e). High-income countries hold the most critical role in realizing these potential savings. Processed plant-based foods and insect protein could also contribute to externality reduction, although less than substitutions with legumes, fruits, and vegetables. The analysis also shows that neglecting the health implications of less environmentally damaging food production underestimates the health advantages of plant-based diets. A substantial portion of the total potential health benefits (avoided DALYs) from dietary shifts stems from the reduction in environmental impacts associated with food production, highlighting the importance of considering both production and consumption effects. The environmental impact drivers were identified as: for human health, agricultural water use; and for ecosystems, water consumption and land use.

The study's findings underscore the significant hidden costs associated with current food production and consumption patterns. Monetarizing these externalities allows for a more comprehensive understanding of the true economic burden and facilitates cross-domain comparisons. The results demonstrate the potential of dietary changes to mitigate climate change and simultaneously reduce wider environmental impacts on human health and ecosystem quality. The significant economic incentive to support a transition to low-carbon diets is highlighted by the substantial monetary value of potential externality savings. The strong link between diets and health, both directly through consumption and indirectly through food production's environmental impacts, is reinforced. While the highest potential savings are found in high-income countries, the study emphasizes the need for sustainable practices in all income groups, especially in developing countries where addressing undernourishment and nutritional deficiencies is paramount. The potential of processed plant-based foods and insects as ASF substitutes is noted, but the limitations of these substitutions in terms of overall externality reduction and potential health impacts are also acknowledged.

This research highlights the substantial external costs embedded in current global diets and demonstrates the significant economic and environmental benefits of transitioning to low-carbon diets, particularly those with reduced ASF consumption. Considering both production-related and consumption-related health effects is crucial for a complete appraisal of the benefits of dietary change. The study underscores the need for policies and initiatives that incentivize shifts toward more sustainable food systems, including promoting plant-based alternatives, improving sustainable livestock farming practices, and addressing the 'disgust' factor regarding insect consumption in certain regions. Future research could investigate the dynamic interplay between dietary changes, agricultural practices, and the broader socio-economic implications of such shifts.

The study's results are subject to certain limitations. The cradle-to-gate LCA approach may underestimate the total environmental impacts by excluding retail and use stages. The reliance on global average impact intensities for many countries introduces uncertainty, particularly in regions with limited LCI data. The monetarization of DALYs and species loss involves inherent uncertainties, and the assumptions made in the comparative risk assessment approach could influence the results. The scenarios presented do not represent specific dietary recommendations but rather hypothetical shifts for illustrating potential externality reductions. Finally, the study assumes no changes in agricultural practices in the models, which might underestimate or overestimate impacts depending on the shifts.