Intra- and Interindividual variability in postprandial blood Amino Acid kinetics in healthy young adults after ingestion of a good and a moderate digestible protein source

Background and objectives. Measuring appearance of postprandial amino acids levels is relatively easy to perform and is already used by many science groups all over the world as an indication of the quality of a protein source. However considerable variation in postprandial amino acid kinetics can be expected between individuals due to, amongst others, differences in an individual’s digestion and absorption capacity. As more attention should be given to inter-individual variation of nutrient uptake, this study aimed to quantify the variation in postprandial AA profiles between and within individuals after consumption of a good (whey) and moderate (lucerne) digestible protein source.
Methods. In this randomised, cross-over, double blind, controlled trial 18 young healthy adults visited the research unit on five occasions to consume a 20 g protein drink. Three times lucerne and two times whey, in random order, with a washout period of one week. Blood was collected before and up-to five hours after protein consumption. Blood amino acid kinetics of free amino acids totals were calculated as Area Under the Curve (AUC, corrected for baseline), maximum peak height, and time to peak, using an AA response package in R.
Results. On average, lucerne was associated with ~ 50% lower postprandial AA profile (AUC), a lower peak height and a delayed time to peak compared to whey. However substantial variation between individuals was observed, with the AUC for whey being 2.1 and 1.7 times higher for the highest versus the lowest subject for AA totals (TAA) and essential AA (TEAA) respectively. For lucerne protein these differences were 3.1 and 2.4 times for TAA and TEAA. Also substantial within individuals (‘day-to-day’) variation was seen, with the intra-individual variation being lower than the inter-individual variation for whey, but both being of a comparable magnitude for the lucerne protein drink. Finally, there was little to no correlation between the response (AUC) on the two proteins sources (r<0.20); in other words those with a high AUC for one protein source were not necessarily those with a high AUC for the other protein source.
Conclusions. Postprandial amino acid appearance after ingestion of 20 gram of protein is associated with substantial variation between individuals, as well as within individuals. This appears to be larger for a protein with a low digestibility, i.e. lucerne compared to whey. These results indicate that single blood amino acid profiles should be interpreted with caution as an indication of a protein’s quality, but also warrants further investigation in the – biological - factors that underlie this variation.