Intragastric protein administration stimulates overnight muscle protein synthesis in elderly men.
Am J Physiol Endocrinol Metab. 2011 Sep 13. [Epub ahead of print] Groen BB, Res PT, Pennings B, Hertle E, Senden JM, Saris WH, van Loon LJ.
Background: The loss of skeletal muscle mass with aging has been attributed to an impaired muscle protein synthetic response to food intake. Therefore, nutritional strategies are targeted to modulate postprandial muscle protein accretion in the elderly. Objective: To assess the impact of protein administration during sleep on in vivo protein digestion and absorption kinetics and subsequent muscle protein synthesis rates in elderly men. Design: 16 healthy elderly men were randomly assigned to an experiment during which they were administered a single bolus intrinsically L-[1-(13)C]-phenylalanine labeled casein protein (PRO) or a placebo (PLA) during sleep. Continuous infusions with L-[ring-(2)H(5)]-phenylalanine and L-[ring-(2)H(2)]-tyrosine were applied, to assess in vivo dietary protein digestion and absorption kinetics and subsequent muscle protein synthesis rates during sleep. Results: Exogenous phenylalanine appearance rates increased following protein administration. The latter stimulated protein synthesis, resulting in a more positive overnight whole body protein balance (0.30±0.1 vs 11.8±1.0 μmol phenylalanine·kg(-1)·h(-1) in PLA and PRO, respectively; P<0.05). In agreement, overnight muscle protein fractional synthesis rates were much greater in the PRO experiment (0.045±0.002 vs 0.029±0.002 %·h(-1) respectively; P<0.05) and showed abundant incorporation of the amino acids ingested via the intrinsically labeled protein (0.058±0.006 %·h(-1)). Conclusion: This is the first study to show that dietary protein administration during sleep is followed by normal digestion and absorption kinetics, thereby stimulating overnight muscle protein synthesis. Dietary protein administration during sleep stimulates muscle protein synthesis and improves overnight whole-body protein balance. These findings may provide a basis for novel interventional strategies to attenuate muscle mass loss.
