Mortality co-benefits of dietary shifts under contrasted trajectories toward net-zero emission in France by 2050

BackgroundFood systems--particularly livestock production--account for substantial greenhouse gas (GHG) emissions, while unhealthy diets, characterized by excessive animal-based and insufficient plant-based food consumption, are a major risk factor for all-cause mortality in Europe. Implementing climate mitigation policies related to the GHG emissions of the food system could therefore bring important health co-benefits. MethodsWe developed a health impact assessment model based on a life table approach and evaluated the mortality impact of transitions in food consumption through four contrasting scenarios leading to net-zero GHG emissions for France in 2050. These involved varying dietary shifts, all moving toward more plant-based foods. For each scenario, we modeled the evolution of the diet, as well as the impacts on all-cause mortality by applying the most recent and robust dose-response relationships derived from meta-analyses for 13 food groups. FindingsThe different trajectories of dietary shifts translated into a health impact ranging from 19% [uncertainty interval, UI: 17%-21%] to 24% [UI: 21%-26%] of all-cause mortality prevented in 2050 in the French population. Variation in intakes of nuts, red meat, processed meat, whole grains and legumes bring most of the health benefits. Whatever the parameters chosen in the sensitivity analyses, the results remained robust, with about 100,000-200,000 deaths that could be prevented yearly by 2050 in France. InterpretationThe present study highlights the considerable potential health benefits that trajectories toward net-zero emissions can bring, especially through shifts toward sustainable diets. These results reinforce the strong convergence of environmental and human health issues in the agri-food sector. FundingFrench High Council for the Future of Health Insurance (HCAAM) and the National Agency for Ecological Transition (Ademe). Research in contextO_ST_ABSEvidence before this studyC_ST_ABSFood systems are a significant contributor to climate change and in parallel, dietary risks are one of the leading causes of all-cause mortality globally, notably in high-income countries such as France. A recent systematic review by Moutet et al. revealed that only two studies evaluating health co-benefits through dietary shifts in net-zero GHG emissions scenarios were published to date. This suggests a convergence and a possible win-win situation between climate change and human health challenges regarding food production and consumption. In order to face the climate crises, governments around the world, and particularly those of the countries historically the largest contributors to climate change, must cut their greenhouse gas emissions to achieve net-zero emission by 2050. Dietary shifts would be a major driver to pursue this objective and could bring important health benefits to the population conducting these changes. For instance, Hamilton et al. showed that dietary changes in line with the Paris Agreements could result in 188 deaths prevented per 100,000 persons in 2040 in Germany and 141 in the UK. Added value of this studyOf the two previously published studies, only one assumed a gradual implementation of changes in diets, combined with a time lag in health effects. We also made these assumptions and considered the gradual change in consumption of thirteen food groups for which recent meta-analyses provided all-cause mortality dose-response relationships with a high level of quality. This study is also among the first to combine nutritional and environmental optimization, through four scenarios; all of which are expected to lead to net-zero emission by 2050 via very contrasting climate change mitigation trajectories. Nevertheless, all of them require a dietary shift toward more plant-based foods. We conducted a health impact assessment for France and showed that achieving net-zero emission by 2050 while considering nutrition references set by national guidelines would provide health co-benefits. Depending on the scenarios, health gains could range from 19% to 24 % of all-cause mortality prevented in the adult French population in 2050, compared to a scenario assuming that we would maintain the current observed dietary habits in the future. Implications of all the available evidenceThis study adds to the available evidence that taking action to mitigate climate change is an opportunity to strongly improve public health. Engaging populations in a shift toward a healthier and more sustainable diet could bring major human health and environmental benefits.