In search of indicators to assess the environmental impact of diets

The aim of this paper is to identify a set of crucial indicators to assess the most pressing environmental impacts of diets. Based on a literature review, 55 potential assessment methods were selected and their distinctive indicators identified. The methods were classified according to their position in the DPSIR framework [chain of Drivers, Pressures, State (changes), Impacts, and Responses], and into 15 environmental issues at three levels. The selection was narrowed down to eight, based on the availability of reliable methods, their relevance to agri-food systems, their frequent application for diets, and their recommendation by international bodies. (1) At the global (supra) level, the planetary boundaries approach addresses the current global environmental (change in) state and helps to prioritize the most pressing issues related to the agri-food system as a driver. These issues are climate change, nitrogen and phosphorus cycle disruption, land-use change, and freshwater use. (2) At the national (macro) level, the footprints approach is used to identify indicators. This footprint family includes ecological, land, carbon, energy, and water footprints. International bodies support these key indicators, but they recommend complementary assessment methods for nitrogen and phosphorus flows, soil health, and pesticide use. (3) At the product (micro) level, life cycle assessment includes 11 pressure indicators. Of the latter, greenhouse gas emissions (GHGEs) and land use (LU) are the most frequently used indicators in diet studies. We conclude that GHGEs and LU fulfill the selection criteria and address most of the environmental impact of diets well. In the future, these indicators should be supplemented with an indicator addressing the nitrogen and phosphorous efficiency of food products.