Relative environmental impacts and monetary cost of food categories: Functional unit matters

The aim of this study was to explore how the choice of a functional unit (FU) influences the environmental and economic rankings of food categories. For each adult in the latest French national dietary survey (n = 2121), we built a dataset providing the energy and nutritional content, environmental impacts (14 metrics) and monetary cost of 20 food categories as consumed. The cost and environmental impacts of each food category were expressed for each individual according to 4 general FUs (1 kg, 100 kcal, 1 portion, 1 nutritional quality unit) and 9 nutrient-specific FUs (e.g., 50 g of proteins), and categories were ranked according to their median impact or cost. Cost and environmental rankings of food categories differed according to the FU (especially with nutrient-specific ones). Despite such heterogeneous rankings, some results were generally consistent: compared to other food categories, legumes, potatoes and whole grains were less expensive and less impacting, meats (especially ruminant ones) were more expensive and more impacting, and dairy and eggs had intermediate cost and environmental impacts. By providing a wide overview of different “metric × FU” situations, this study contributes to answering the important question of the right FU to use when evaluating the sustainability of food.