Re-evaluating the importance of protein quality: insights on its limited role in multi-nutrient functional units

Abstract Purpose Changes in the consumption of protein-rich foods are needed due to their high environmental impacts. However, proteins are indispensable for human nutrition, and there is notable variation in the protein quality of protein-rich foods. The methods to consider protein quality in Nutritional Life Cycle Assessment (nLCA) are still developing. In this study, we assessed the impact of including protein quality in single- and multi-nutrient nutritional functional units (nFUs) in an LCA of products and meals. Methods We conducted an LCA with four different nFUs: protein content, protein content adjusted for protein quality, nutrient index for protein-rich foods, and the same nutrient index adjusted for protein quality. To assess the protein quality of the food products Digestible Indispensable Amino Acid Score (DIAAS) was used. The assessed food products were patties with beef, pork, chicken, trout, perch, chickpea, and soymeal as the main ingredients. The assessments were also done at meal-level, including a side dish of potatoes and mixed salad. Results and discussion Animal-based foods were of higher protein quality. When protein quality was included in the single-nutrient nFU, i.e. protein content, in nLCA, the climate impact decreased for animal-based products and increased for plant-based products. At meal-level, the trend was similar; however, the overall protein quality of meals was lower in comparison to the patties. When including protein quality correction in the nutrient index, there were little to no changes in the index score, resulting in little to no difference in the climate impact. Conclusions Protein-rich foods vary in protein quality, and thus, adjusting protein content with protein quality in nLCAs might be of interest when assessing only one nutrient, i.e. protein. However, we recommend it as an additional measure as there are notable limitations in assessing protein quality. Instead, when assessing multiple nutrients, as in nutrient indices, adding digestibility of protein into the index might not bring additional value to nLCA.