The influence of optimal dietary protein intake for muscle metabolism across the lifespan

Mathewson, Sophie L. (2023). The influence of optimal dietary protein intake for muscle metabolism across the lifespan. University of Birmingham. Ph.D.

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Abstract

Research has demonstrated a deterioration of skeletal muscle mass and function with increasing age (termed ‘sarcopenia’), and protein nutrition, in particular amount and source of protein, has been highlighted as a key factor regulating its progression. This thesis endeavours to explore the role of protein dose and source on muscle metabolism across the lifespan; from younger adults to frail older adults in care homes. Chapter 2 of this thesis explores the causes of protein-energy malnutrition in the residential care setting and evaluates the interventional literature targeting this. A review of the literature establishes that oral nutritional supplementation and protein-fortified foods are most commonly used to increase daily protein intake in care home residents. However, the effectiveness of these on musculoskeletal health outcomes and their compliance rates are unclear and conflicting due to the complexity in carrying out interventional work in this setting. Chapter 3 of this thesis investigates the role of habitual dietary protein intake on physiological muscle parameters in healthy older adults, with results suggesting that there are no differences between the habitual protein intakes of these two populations. However, whole-body lean mass and knee extensor strength were significantly higher in younger adults, suggesting that in recreationally active, healthy older adults, other factors aside from habitual protein intake are playing a role in regulation of muscle metabolism. To further explore this, Chapter 4 aims to develop a human serum ex vivo C2C12 co-culture model to explore the use of fasted vs. fed serum to investigate muscle responsiveness to feeding, with results demonstrating negligible differences between serum conditions. Further optimisation of this model is needed, with no clear protocol for AA starvation period, serum treatment concentration, nor media glucose content yet identified. The final data chapter of this thesis explores the amino acid (AA) kinetics in young and older adults following ingestion of a vegan-blend and whey protein, and highlights a lower circulating concentration of several AAs, including leucine, following consumption of a vegan-blend protein in comparison to a whey protein, with little effect of age. Further investigation confirmed the muscle protein synthesis (MPS) response of C2C12 myotubes to AA treatment mimicking vegan and whey protein compositions. However, when ‘preconditioning’ C2C12 myotubes with young and older adult fasted serum prior to AA treatment, there is negligible age nor protein source differences in the myotube MPS response.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):