For design of healthy and sustainable diets and food systems, it is important to consider not only the quantity but also the quality of nutrients. This is particularly important for proteins, given the large variability in amino acid composition and digestibility between dietary proteins. This article reviews measurements and metrics in relation to protein quality, but also their application. Protein quality methods based on concentrations and digestibility of individual amino acids are preferred, because they do not only allow ranking of proteins, but also assessment of complementarity of protein sources, although this should be considered only at a meal level and not a diet level. Measurements based on ileal digestibility are preferred over those on faecal digestibility to overcome the risk of overestimation of protein quality. Integration of protein quality on a dietary level should also be done based on measurements on an individual amino acid basis. Effects of processing, which is applied to all foods, should be considered as it can also affect protein quality through effects on digestibility and amino acid modification. Overall, protein quality data are crucial for integration into healthy and sustainable diets, but care is needed in data selection, interpretation and integration.

Current evaluation systems for protein quality focus only on indispensable amino acids (IAAs) and do not consider the dispensable amino acids (DAAs). However, at excess levels of IAAs, DAAs may become limiting. Here, we used published ileal amino acid digestibility data determined in growing pigs and currently assumed protein and IAA recommendations to estimate utilizable, oxidized, and non‐absorbed amino acids in different dietary protein and to compare these utilizable amino acid values to digestible indispensable amino acid score (DIAAS) values. For dietary protein sources with a DIAAS value 90, the amount of utilizable amino acid stays within the range 800–1000 mg/g protein. Cereals contained the lowest levels of utilizable amino acids and the highest amount of oxidized amino acids. Dairy and meat have the highest amount of utilizable amino acids followed by nuts and pulses. For many mixtures of protein sources, the highest value for utilizable amino acids, which considers both IAAs and DAAs, occurred at a different ratio of protein sources than the maximum DIAAS value, which only considers IAAs. From this theoretical study and based on the assumptions made, we conclude that estimation of utilizable amino acids from data typically reported in DIAAS studies further enables complementary insights next to DIAAS values. Careful consideration of protein and IAA requirements is critical in further work.

Critically ill patients in the Intensive Care Unit (ICU) should receive nutritional support matched to their metabolic needs as both under- and overfeeding energy has been shown to increase mortality. Critical illness can significantly affect metabolism. Consequently, resting energy expenditure (REE) can vary markedly during critical illness. Therefore, indirect calorimetry to estimate REE is recommended to determine energy requirements in individual ICU patients and to guide optimal nutritional support. Currently, the Quark metabolic monitor is considered the gold standard in our ICU, but novel mechanical support devices are also equipped with indirect calorimetry functionalities. This study aimed to evaluate the performance of a currently unevaluated device. A cross-sectional analysis in mechanically ventilated patients was conducted in a mixed medical-surgical ICU. The primary outcome was a numerical and visual comparison of the performance of the Beacon indirect calorimeter to calculate REE compared to the Quark device using Bland Altman plots. Performance was evaluated using bias, precision, accuracy, and reliability. Secondary analysis included a comparison with REE estimated by predictive equations. Seventy-one measurements were obtained in 27 mechanically ventilated subjects. An underestimation by the Beacon device in calculated REE of -96.2 kcal/day (4.5%) was found. There was a bias towards higher VCO₂ and lower VO₂ values with Beacon as compared to Quark. The reliability of the Beacon was good, with an absolute intraclass correlation coefficient of 0.897 (95%CI 0.751-0.955; p = 0.000). There was a poor correlation (<0.40) between the separate indirect calorimetry devices and most predictive equations. Only the Faisy predictive equations had good reliability (ICC 0.687, p = 0.002). Beacon indirect calorimetry accurately determined REE in mechanically ventilated critically ill patients compared to the gold standard in our ICU (Quark indirect calorimeter), although confidence intervals were wide. There was low bias and good reliability. On the other hand, predictive equations performed poorly compared to both devices, underestimating the true metabolic needs of mechanically ventilated ICU patients.