Pennings B, Groen B, de Lange A, Gijsen AP, Zorenc AH, Senden JMG, van Loon LJC. Amino acid absorption and subsequent muscle protein accretion following graded intakes of whey protein in elderly men. protein ingestion has been shown to effectively stimulate postprandial muscle protein accretion in older adults. However, the impact of the amount of whey protein ingested on protein digestion and absorption kinetics, whole body protein balance, and postprandial muscle protein accretion remains to

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... e established. We aimed to fill this gap by including 33 healthy, older men (73 Ϯ 2 yr) who were randomly assigned to ingest 10, 20, or 35 g of intrinsically L-[1-13 C]phenylalanine-labeled whey protein (n ϭ 11/treatment). Ingestion of labeled whey protein was combined with continuous intravenous L-[ring-2 H5]phenylalanine and L-[ring-2 H2]tyrosine infusion to assess the metabolic fate of whey protein-derived amino acids. Dietary protein digestion and absorption rapidly increased following ingestion of 10, 20, and 35 g whey protein, with the lowest and highest (peak) values observed following 10 and 35 g, respectively (P Ͻ 0.05). Whole body net protein balance was positive in all groups (19 Ϯ 1, 37 Ϯ 2, and 58 Ϯ 2 mol/kg), with the lowest and highest values observed following ingestion of 10 and 35 g, respectively (P Ͻ 0.05). Postprandial muscle protein accretion, assessed by L-[1-13 C]phenylalanine incorporation in muscle protein, was higher following ingestion of 35 g when compared with 10 (P Ͻ 0.01) or 20 (P Ͻ 0.05) g. We conclude that ingestion of 35 g whey protein results in greater amino acid absorption and subsequent stimulation of de novo muscle protein synthesis compared with the ingestion of 10 or 20 g whey protein in healthy, older men. nutrition; aging; sarcopenia; fractional synthetic rates; stable isotopes AGING IS ACCOMPANIED BY a progressive decline in skeletal muscle mass, termed sarcopenia (15). Data have been obtained to suggest that the skeletal muscle protein synthetic response to food intake is impaired in older adults (7, 12) . This proposed anabolic resistance is now regarded a key factor in the etiology of sarcopenia. Consequently, we and other laboratories have been trying to define effective interventional strategies to compensate for this anabolic resistance by improving postprandial muscle protein accretion in older adults (14, 20, 22, 23) . Recently, we assessed the impact of protein digestion and absorption kinetics as well as amino acid composition on postprandial muscle protein synthesis rates in older men. The results showed that whey protein was more effective than either casein or casein hydrolysate protein in stimulating postprandial muscle protein accretion (19).