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Failure of muscle mass maintenance in older adults is attributed to anabolic resistance, or a weakened protein synthetic response to anabolic stimuli. Leucine, an amino acid, is a key food-related anabolic stimulus. There is a scarcity of data on muscle protein synthesis (MPS) following the administration of a single bolus of leucine in aged population. Additionally, long-term single leucine supplementation does not seem to increase muscle mass.
A study by Dijk et al evaluated the MPS response to the administration of a single bolus of leucine or leucine combined with whey protein, in aged experimental models.
Overnight fasted models were administered an oral gavage with leucine or whey-protein enriched with leucine or 0.5 mL water (fasted control). Investigators assessed amino acid concentrations in plasma and right muscle tibialis anterior (TA). MPS and phosphorylation rate of Akt, 4E-BP1 and p70S6k were assessed in left TA.
In aged models, leucine administration did not increase MPS, despite a 6-fold increase in plasma leucine and elevated muscle free leucine levels. However, leucine-enriched whey protein significantly stimulated MPS. Additionally, muscle free EAA, NEAA and the phosphorylation rate of Akt, 4E-BP1 and p70S6k were found to be significantly enhanced only after administration of leucine-enriched whey protein.
The study thus revealed that leucine-enriched whey protein stimulates MPS in aged models but leucine administration does not do so.
- Dijk FJ, van Dijk M, Walrand S, et al. Differential effects of leucine and leucine-enriched whey protein on skeletal muscle protein synthesis in aged mice. ClinNutr ESPEN. 2018 Apr;24:127-133.