Dietary protein digestion and absorption kinetics are not impaired after exercise or at an older age. Exercising before protein intake allows for a greater use of dietary protein-derived amino acids for de novo muscle protein synthesis in both young and elderly men. This trial was registered at clinicaltrials.gov as NCT00557388.

Timed protein supplementation immediately before and after exercise does not further augment the increase in skeletal muscle mass and strength after prolonged resistance-type exercise training in healthy elderly men who habitually consume adequate amounts of dietary protein. This trial was registered at clinicaltrials.gov as NCT00744094.

This is the first study to show that protein ingested immediately before sleep is effectively digested and absorbed, thereby stimulating muscle protein synthesis and improving whole-body protein balance during postexercise overnight recovery.

During postexercise recovery, optimal nutritional intake is important to replenish endogenous substrate stores and to facilitate muscle-damage repair and reconditioning. After exhaustive endurance-type exercise, muscle glycogen repletion forms the most important factor determining the time needed to recover. Postexercise carbohydrate (CHO) ingestion has been well established as the most important determinant of muscle glycogen synthesis. Coingestion of protein and/or amino acids does not seem to further increase muscle glycogensynthesis rates when CHO intake exceeds 1.2 g · kg -1 · hr -1 . However, from a practical point of view it is not always feasible to ingest such large amounts of CHO. The combined ingestion of a small amount of protein (0.2-0.4 g · kg -1 · hr -1 ) with less CHO (0.8 g · kg -1 · hr -1 ) stimulates endogenous insulin release and results in similar muscle glycogen-repletion rates as the ingestion of 1.2 g · kg -1 · hr -1 CHO. Furthermore, postexercise protein and/or amino acid administration is warranted to stimulate muscle protein synthesis, inhibit protein breakdown, and allow net muscle protein accretion. The consumption of ~20 g intact protein, or an equivalent of ~9 g essential amino acids, has been reported to maximize muscle protein-synthesis rates during the first hours of postexercise recovery. Ingestion of such small amounts of dietary protein 5 or 6 times daily might support maximal muscle protein-synthesis rates throughout the day. Consuming CHO and protein during the early phases of recovery has been shown to positively affect subsequent exercise performance and could be of specific benefit for athletes involved in multiple training or competition sessions on the same or consecutive days.

Impaired digestion and/or absorption of dietary protein lowers postprandial plasma amino acid availability and, as such, could reduce the postprandial muscle protein synthetic response in the elderly. We aimed to compare in vivo dietary protein digestion and absorption and the subsequent postprandial muscle protein synthetic response between young and elderly men. Ten elderly (64 +/- 1 y) and 10 young (23 +/- 1 y) healthy males consumed a single bolus of 35 g specifically produced, intrinsically l-[1-(13)C]phenylalanine-labeled micellar casein (CAS) protein. Furthermore, primed continuous infusions with l-[ring-(2)H(5)]phenylalanine, l-[1-(13)C]leucine, and l-[ring-(2)H(2)]tyrosine were applied and blood and muscle tissue samples were collected to assess the appearance rate of dietary protein-derived phenylalanine in the circulation and the subsequent muscle protein fractional synthetic rate over a 6-h postprandial period. Protein ingestion resulted in a rapid increase in exogenous phenylalanine appearance in both the young and elderly men. Total exogenous phenylalanine appearance rates (expressed as area under the curve) were 39 +/- 3 mumol.6 h.kg(-1) in the young men and 38 +/- 2 mumol.6 h.kg(-1) in the elderly men (P = 0.73). In accordance, splanchnic amino acid extraction did not differ between young (72 +/- 2%) and elderly (73 +/- 1%) volunteers (P = 0.74). Muscle protein synthesis rates, calculated from the oral tracer, were 0.063 +/- 0.006 and 0.054 +/- 0.004%/h in the young and elderly men, respectively, and did not differ between groups (P = 0.27). We conclude that protein digestion and absorption kinetics and the subsequent muscle protein synthetic response following the ingestion of a large bolus of intact CAS are not substantially impaired in healthy, elderly men.