Protein and diet quality for muscle health and quality of life during ageing

  • Rachel Reid-McCann

Student thesis: Doctoral ThesisDoctor of Philosophy


Sarcopenia, the condition of age-related decline in muscle mass and strength, is estimated to affect 10-27% of those over the age of 60 and is associated with a range of adverse outcomes including reduced quality of life (QoL), disability and death. There is evidence that protein may improve muscle mass and strength alongside exercise, however the role of protein source is unclear. Limited observational evidence suggests that diet quality may also be protective of muscle health and quality of life, however experimental studies are needed to test this hypothesis, especially in older adults at nutritional risk who may benefit most from a dietary intervention.

Chapter 1: Literature review. Chapter 2: Systematic review and meta-analysis of RCTs which compared the effects of plant versus animal protein interventions on muscle mass, strength, physical performance and sarcopenia in adults aged 18 and over. Chapter 3: Intervention development for the PROMED-EX trial [Registration: NCT05166564], including establishment of a Personal and Public Involvement (PPI) group, development of written dietary education materials tailored for older adults, pilot testing of a commercial multimodal exercise programme (ExWell Medical) in the PROMED-EX target population of older adults at risk of undernutrition, and lastly, identification of optimal outcome measures for muscle mass, strength, physical performance, QoL and diet quality. Chapter 4: PROMED-EX recruitment strategy and statistical analysis of baseline demographics and nutrient intake, and effects of three months’ diet intervention, with (“PROMEDEX”) or without (“PROMED”) multimodal home-based exercise, on nutrient intake, diet quality, muscle mass, strength, physical performance, sarcopenia and QoL.

Systematic review (n=36 RCTs) and meta-analysis (n=19 RCTs) found no difference in the effect of plant or animal protein for muscle mass in younger (<50 years) or older (>50 years)populations, or for strength. Assessment of recruitment strategies for the PROMED-EX trial revealed that collaboration with primary care stakeholders was the most successful method. No participants in this PROMED-EX subsample (n=52) had sarcopenia. Both PROMED-EX and PROMED groups significantly increased protein intake and diet quality. The PROMED group significantly improved mental health related QoL. Muscle mass and strength did not change in response to interventions.

Most trials reviewed in Chapter 2 compared soy to milk protein, therefore these findings may not be extrapolated to all plant and animal proteins and future research is warranted into effects of different protein sources, e.g., non-soy legumes. Analysis of approximately half of the PROMEDEX sample (n=52/105) indicated that the PROMED diet is successful for increasing protein intake and diet quality, and potentially mental health. Further beneficial effects may be elucidated in final analysis after six months of intervention, aimed to be completed by May 2024.

Thesis is embargoed until 31 December 2024.

Date of AwardDec 2023
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsNorthern Ireland Department for the Economy
SupervisorMichelle McKinley (Supervisor) & Claire McEvoy (Supervisor)


  • Sarcopenia
  • muscle health
  • quality of life
  • healthy ageing
  • nutrition
  • protein

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