The importance of dietary protein quality for skeletal muscle anabolism in older adults

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Korzepa, Marie ORCID: https://orcid.org/0000-0002-6775-0645 (2024). The importance of dietary protein quality for skeletal muscle anabolism in older adults. University of Birmingham. Ph.D.

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Abstract

The age-related loss of skeletal muscle mass and strength, termed sarcopenia, is underscored by impairments in muscle protein turnover which presents as type II muscle fibre atrophy. Specifically, a blunted muscle anabolic response to dietary protein ingestion is suggested as a key driver of sarcopenia progression but the intracellular mechanisms remain unclear. Sarcopenia progression may be attenuated through dietary protein intake at or above 1.2 g·kg body mass[BM]-1day-1 and partaking in resistance exercise training (RET), but these strategies may not be feasible for many older adults. In this thesis, Chapter 2 uses immunofluorescence microscopy (IF) to compare the localisation and abundance of mechanistic target of rapamycin (mTOR)-related intracellular signalling targets on a fibre type-specific basis in rested skeletal muscle of young (YM) and old (OM) men. The abundance of each target was similar between fibre types, although in OM mTOR abundance was lower than YM, whereas tuberous sclerosis complex 2 and Ras homolog enriched in brain (Rheb) were greater, whilst Rheb localisation at the muscle fibre periphery also differed between YM and OM. This chapter highlights that IF has the capacity to identify age-related alterations in intracellular signalling protein abundance and localisation, which may underly impairments in muscle anabolism implicated in the progression of sarcopenia. Chapter 3 provides a narrative review highlighting barriers to increasing dietary protein intake beyond general population-wide guidelines and participating in RET. Considering these barriers, emphasising the consumption of higher quality protein sources (i.e., those with a complete essential amino acid (EAA) profile that is readily bioavailable) may support greater postprandial muscle anabolism, particularly in scenarios where protein intake is well below recommendations, such as with ill-health and disuse. Considering the proposed importance of dietary protein source, Chapter 4 explored the postprandial amino acid (AA) and appetite regulatory response to a very low protein-containing whole food mixed breakfast supplemented with a small bolus of higher quality whey protein concentrate (MB+WPC) or lower quality pea protein isolate (MB+PPI) smoothie in middle-to-older aged adults. Plasma total and EAA excursions and their overall availability over 180 minutes postprandially were not different between groups. However, plasma leucine availability was greater following MB+WPC. Perceived hunger and satiety responses, and plasma concentrations of appetite regulatory hormones were transiently altered following MB+WPC and MB+PPI but did not differ between groups. Greater postprandial plasma leucinemia with MB+WPC over MB+PPI could indicate a superior capacity for muscle anabolic stimulation in middle-to-older aged adults, without adverse effects on appetite. To investigate the suggestions of the preceding chapter, Chapter 5 determined free-living daily rates muscle protein synthesis (iMyoPS) in middle-to-older aged adults consuming a 10-day diet containing 1 g·kg BM-1·day-1 of protein. Meals and a snack were supplemented with a small bolus of higher-quality whey protein concentrate (HQ-D) or lower-quality pea protein isolate (LQ-D). Frequent unilateral RET sessions were performed over the 10-day dietary intervention. Daily rates of iMyoPS were similar between HQ-D and LQ-D in the untrained leg, but greater in the trained over the untrained leg in both groups. Changes in muscle adaptive remodelling, body composition and whole-body nitrogen balance were absent and/or indistinguishable between groups. In a typical lower protein-containing diet of healthy middle-to-older aged adults, the quality and source of ingested protein does not modulate rested or RET-induced iMyoPS rates over a 10-day period. Nonetheless, frequent RET augments daily rates of iMyoPS over a 10-day lower protein-containing diet and represents a potent strategy to mitigate age-related muscle deterioration.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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