Postprandial plasma amino acid and appetite responses to a low protein breakfast supplemented with whey or pea protein in middle-to-older aged adults

The addition of low-dose protein to low protein-containing meals in middle-to-older aged adults may promote greater postprandial plasma aminoacidemia and mitigate declines in muscle health but may be dependent on the source and quality of protein consumed. This single-blind randomised study investigated postprandial plasma aminoacidemia and appetite regulatory responses to a typical lower protein-containing (∼0.07 g·kg body mass[BM]^-1) mixed breakfast supplemented with ∼0.13 g·kg BM^{- 1} of whey protein concentrate (MB + WPC) or pea protein isolate (MB + PPI) in middle-to-older aged adults. Venous blood samples were collected whilst fasted and over a 180-min postprandial period to determine plasma amino acid and appetite hormone concentrations. Perceived appetite ratings were measured using Visual Analogue Scales. Plasma total amino acids and essential amino acids increased over time (both P < 0.05) with no between-group differences or overall availability over 180 min (incremental area under the curve (iAUC)). Plasma leucine concentrations increased over time (both P < 0.05) with greater peak concentrations (P = 0.032) and iAUC (P = 0.012) in MB + WPC compared with MB + PPI. Plasma total-ghrelin and total-GLP-1 concentrations and perceived ratings of hunger, fullness, and satiety were transiently altered following MB + WPC and MB + PPI (P < 0.05 for all), with no differences between groups. In middle-to-older aged adults, co-ingesting a small bolus of whey protein alongside a typical lower protein-containing breakfast elicits greater plasma leucinemia than co-ingestion of pea protein, with no differential impact on appetite regulation. Whether the addition of low-dose whey protein to typical meals of middle-to-older aged adults can enhance muscle anabolism without adversely affecting appetite remains to be determined.