Intra- and interindividual variability in postprandial plasma amino acid kinetics after ingestion of whey and lucerne protein in healthy young adults

Protein intake and the resulting postprandial aminoacidemia are important anabolic stimuli. However, considerable individual variation in postprandial amino acid (AA) kinetics can be expected due to, amongst others, differences in an individual’s digestion and absorption capacity. Therefore, we 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. Eighteen healthy young adults consumed a 20 g protein drink on five occasions (3x lucerne and 2x whey) in a randomised, cross-over, double-blind trial. Blood was collected before and up-to five hours after protein consumption. Plasma free AA kinetics were calculated as incremental Area Under the Curve (iAUC), maximum peak height, and time to peak, using an AA response package in R. Peak height and iAUC were significantly greater for whey compared to lucerne, for both total AAs and total indispensable AAs (TIAAs) (p < 0.001). The total IAA AUC of lucerne was only 51.6% of that of whey, confirming the low IAA availability of lucerne as a protein source. For whey, the inter-person variability in iAUC (SD: 1110.5 for TIAAs) was higher than the intra-person variability (SD: 604.6 for IAAs), indicating that differences between participants were larger than within participants. Likewise, for lucerne the inter-person variability of TIAAs was larger (SD: 703.4 vs 553.1 for inter- and intra-person variability). There was little-to-no correlation between the iAUC of whey and lucerne (r<0.20), suggesting that subjects with a high iAUC for one protein source were not necessarily those with a high iAUC for the other protein source. These results confirm the low (I)AA availability of lucerne compared to whey, and indicate that variation in postprandial AA kinetics should not be neglected and insights in this variation is warranted to support future optimized protein intake advice to prevent deficiency.