Sustainable diets: are nutritional objectives and low-carbon-emission objectives compatible?

Food systems in developed countries face one major challenge, namely the promotion of diets that are both healthy and generate less greenhouse gas emissions (GHGE). In this article, we review papers evaluating the impact of a change in diets on both health and GHGE. We address the following questions: How big are the health and environmental impacts that could be induced by a switch to healthier diets? What is, in monetary value, the relative importance of the health impact and the environmental impact? Is it possible to design an economic policy that increases global welfare taking into account externalities on both health and the environment? Since the way the change in diet is modeled is a key issue, we classify papers according to the methodology used for simulating diet changes: ad-hoc scenarios, optimized diets and economic modelling. We find that it is possible to design economic policies that have positive impacts on both dimensions. Because the substitutions / complementarities between food products are complex, it is not granted that a policy targeting one dimension will generate positive effects on the other dimensions. However, given the diversity of substitution and complementarity possibilities between products, it is possible to design a policy that does improve both dimensions. A carbon-based policy that targets the products with a high GHG content (e.g. meat products) and reinvests the revenues collected with the tax to subsidize the consumption of fruits and vegetables is likely to have positive effects on both dimensions.