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Abstract Background: The loss of skeletal muscle mass with aging has been attributed to the blunted anabolic response to protein intake. Presleep protein ingestion has been suggested as an effective strategy to compensate for such anabolic resistance. Objective: We assessed the efficacy of presleep protein ingestion on dietary protein digestion and absorption kinetics and overnight muscle protein synthesis rates in older men. Methods: In a randomized, double-blind, parallel design, 48 older men (mean ± SEM age: 72 ± 1 y) ingested 40 g casein (PRO40), 20 g casein (PRO20), 20 g casein plus 1.5 g leucine (PRO20+LEU), or a placebo before sleep. Ingestion of intrinsically L-[1-13C]-phenylalanine– and L-[1-13C]-leucine–labeled protein was combined with intravenous L-[ring-2H5]-phenylalanine and L-[1-13C]-leucine infusions during sleep. Muscle and blood samples were collected throughout overnight sleep. Results: Exogenous phenylalanine appearance rates increased after protein ingestion, but to a greater extent in PRO40 than in PRO20 and PRO20+LEU (P < 0.05). Overnight myofibrillar protein synthesis rates (based on L-[ring-2H5]-phenylalanine) were 0.033% ± 0.002%/h, 0.037% ± 0.003%/h, 0.039% ± 0.002%/h, and 0.044% ± 0.003%/h in placebo, PRO20, PRO20+LEU, and PRO40, respectively, and were higher in PRO40 than in placebo (P = 0.02). Observations were similar based on L-[1-13C]-leucine tracer (placebo: 0.047% ± 0.004%/h and PRO40: 0.058% ± 0.003%/h, P = 0.08). More protein-derived amino acids (L-[1-13C]-phenylalanine) were incorporated into myofibrillar protein in PRO40 than in PRO20 (0.033 ± 0.002 and 0.019 ± 0.002 MPE, respectively, P < 0.001) and tended to be higher than in PRO20+LEU (0.025 ± 0.002 MPE, P = 0.06). Conclusions: Protein ingested before sleep is properly digested and absorbed throughout the night, providing precursors for myofibrillar protein synthesis during sleep in healthy older men. Ingestion of 40 g protein before sleep increases myofibrillar protein synthesis rates during overnight sleep. These findings provide the scientific basis for a novel nutritional strategy to support muscle mass preservation in aging and disease. This trial was registered at as NTR3885.


Mary MacKillop Institute for Health Research

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Journal Article

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