Résumé
Tunisia is a typical country of the Mediterranean region where high prevalence of overweight, obesity and non-communicable diseases co-exist with some micronutrient deficiencies, and diet-related environmental issues must be addressed. Individual food choices may influence both health and environment. The aim of this study was to identify diets that are nutritionally adequate, culturally acceptable, and with low environmental impact for Tunisian adults. Individual dietary data from a national Tunisian survey on food consumption (n = 7209, 35'70 years) and the national food composition table were used to estimate the food and nutritional content of the mean observed (OBS) diet. The diet environmental impact was assessed through seven metrics: water deprivation, land-use, land-use potential impacts on biodiversity loss, erosion resistance, mechanical filtration, groundwater replenishment, and biotic production. Quadratic optimization models were implemented to obtain diets that met the nutritional recommendations, and concomitantly respected increasingly stringent environmental constraints and minimized the departure from the OBS diet. Without environmental constraints, the nutritional recommendations were met by increasing the amount of dairy, starch and vegetables, and decreasing foods high in fat/salt/sugar (HFSS) and added fat. Compared with the OBS diet, the environmental impact of this diet increased: +32% for water deprivation and +46'48% for land use and its impacts. When a moderate environmental impact reduction ('30%) was added to the nutritional constraints, the dietary changes at the food group level were similar to those required to reach nutritional adequacy, except for a progressive decrease in meat/fish/egg quantities. Animal-based product contributions to the total energy and protein content were close or slightly lower than in OBS diet, but a redistribution of sources was required: less meat in favor of dairy, egg and fish products. Stronger reductions ('40%) required substantial changes that might compromise the optimized diet acceptability. Targeting a nutritionally adequate diet without considering its environmental impact might increase water deprivation, land use and its impacts on biodiversity and soil quality. In Tunisia, moving towards healthy diets with lower environmental impact relied more on redistributing the sources of animal-based products rather than on reducing their total contribution, together with a decrease of HFSS and added fats, and an increase of vegetables. Actions to favor the adoption of such dietary changes by consumers should be explored to promote more sustainable diets in the Mediterranean region.