The effect of nutritional quality on comparing environmental impacts of human diets

We concluded that the nutrient intake resulting from a meal cannot be used to assess the nutritional quality of a daily diet and, hence, the environmental impact of meals cannot be compared to that of daily diets. Studies on meals were therefore excluded from further analysis. Our results further show that daily diets that had higher percentages of ASFP were associated with higher (excess) intakes of total protein and lower values of NRD9.3. Diets that had higher percentages of ASFP were associated with higher GWPs and LU's per gram protein capped and per unit NRD9.3. Without capping protein to the recommended intake level, GWP and LU per gram of protein were generally lower for diets that had higher percentages of ASFP. Without capping, diets with higher percentages of ASFP are credited for overconsumption of protein. Since overconsumption of protein does not benefit health, we recommend capping to the recommended intake level. The effect of using NRD9.3 rather than day as functional unit was small for GWP. For LU we found no effect. When using NRD9.3 as functional unit, it must be considered that this functional unit requires more data than day or protein. Our analysis is based on a limited number of studies. Although initially a substantial number of studies were found, many of these were excluded because insufficient data were provided about diet composition, only one diet scenario was assessed, or because the studies assessed the environmental impact of meals rather than of diets. We found mainly Western-oriented diets, often designed by the researchers and not representative for actual consumption. For further research on the environmental impact of diets, we therefore recommend analysis on representative daily diets.