Kouw IWK, et al. – This study examined the impact of presleep protein ingestion on dietary protein digestion and absorption kinetics and overnight muscle protein synthesis rates in older men. It was observed that in healthy older men, the observed myofibrillar protein synthesis during sleep was the end product of pre–sleep protein ingestion and its proper digestion and absorption throughout the night. Therefore, it was evident that ingestion of 40 g protein before sleep increased myofibrillar protein synthesis rates during overnight sleep.

Methods

• A total of 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, in a randomized, double-blind, parallel design.
• 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.
• Researchers collected muscle and blood samples throughout overnight sleep.

Results

• Findings showed that exogenous phenylalanine appearance rates increased after protein ingestion, but to a greater extent in PRO40 than in PRO20 and PRO20+LEU (P <0.05).
• Data reported that 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).
• Researchers observed that 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 = 0.06.