Investigating muscle protein synthesis using deuterium oxide: The impact of dietary protein interventions across the lifespan.

This review highlights recent advancements in our understanding of muscle protein synthesis (MPS) across the lifespan, with a focus on dietary protein strategies to support muscle health. Given that skeletal muscle is crucial for whole-body metabolism, movement and independence, maintaining muscle mass throughout life is essential. However, the gradual decline in muscle mass and strength with age, known as sarcopenia, represents a significant health concern. Muscle mass is regulated by the balance of MPS and muscle protein breakdown, with dietary protein intake playing a central role in stimulating MPS and maintaining a positive protein balance. Much of our current understanding of protein intake, specifically its quantity, quality and distribution, comes from stable isotope-labelled amino acid methods. These techniques, however, are limited by time constraints and controlled settings, providing only brief snapshots of MPS dynamics. The use of deuterium oxide (D₂O) has provided new insights, enabling long-term measures of muscle protein metabolism in free-living conditions. Measurements of longer-term MPS using D₂O suggest that older adults might benefit from protein intakes of >1.2 g/kg/day to enhance MPS. Additionally, replacing protein in the diet with higher-quality sources or enriching lower protein intakes with leucine can further increase MPS. Nevertheless, discrepancies remain regarding optimal protein requirements and the long-term efficacy of supplementing with enriched suboptimal protein doses. The continued application of D₂O in dietary protein research has the potential to provide further insights into the prolonged effects of various protein strategies on muscle preservation across the lifespan.