Multidisciplinary research into the effects of resistance exercise and whey protein supplementation in healthy older men

Abstract

Introduction: Ageing is associated with declines in skeletal muscle mass, strength and physical function, reductions in components of energy expenditure (EE), and deterioration of metabolic and cognitive function. Two interventions that may mitigate these adverse health outcomes are resistance exercise (RE) and increased dietary protein intake. However, further work is required to determine the synergistic effects compared to each intervention alone. Broadly, the aim of this thesis was to examine the individual and combined effects of RE and whey protein supplementation on components of 24-h energy metabolism, parameters of sarcopenia, and metabolic and cognitive function in healthy older men. Additionally, this thesis aimed to examine potential mechanisms of action.

General methods: Thirty-six healthy older men [(mean ± standard error (SE)) age: 66.9 ± 0.7 y; body mass index (BMI) 25.5 ± 0.4 kg/m²] participated in a 12 week, 4-arm, double-blind, randomised controlled trial (RCT). Participants were randomised to either control (CON, n = 9), whey protein supplementation (PRO, n = 9), RE + control (EX+CON, n = 9), or RE + whey protein supplementation (EX+PRO, n = 9). Resistance exercise was performed twice weekly by participants in the EX+CON and EX+PRO groups. Supplements (PRO, 25 g whey protein
isolate; CON, 23.75 g maltodextrin) were consumed twice daily. For the primary analysis, the four intervention groups were compared. Exploratory analyses were also conducted between pooled exercise (EX+CON + EX+PRO, n = 18) and non-exercise groups (CON + PRO, n = 18), and between pooled whey protein (PRO + EX+PRO, n = 18) and control supplement groups (CON + EX+CON, n = 18). Three individual study chapters were derived from the 12- week RCT.

Study specific methods and results:

Study 1: Investigated the individual and combined effects of RE and whey protein

supplementation on 24-h EE, substrate oxidation, metabolic flexibility, subjective appetite and

glucose homeostasis. Participants (n = 33) resided in respiration chambers for 24 h pre- and

post-intervention. Resistance exercise significantly increased fat-free mass (FFM), resting

metabolic rate (RMR), sedentary EE, and 24-h metabolic flexibility compared to non-exercise.

Additionally, RE also elicited within-group increases in insulin sensitivity and subjective

hunger, and within-group decreases in the energy cost of step exercise and spontaneous

activity. Whey protein supplementation aided maintenance of body mass and reduced FM

compared to control supplement groups pooled. Within-group decreases in the energy cost of

both spontaneous activity and step exercise in the fasted state were also observed following

whey protein supplementation. No negative effects of whey protein supplementation were

observed for either total protein or energy intake (EI), or 24-h subjective appetite. However,

whey protein supplementation did result in an increase in overnight protein oxidation, resulting

in a reduced 24-h protein balance. Consequently, this may be a caveat to longitudinal high

protein diets in the elderly. Combined RE and whey protein supplementation did not

significantly augment changes in body composition, 24-h EE, substrate oxidation or metabolic

flexibility, or glucose homeostasis compared to either RE or whey protein supplementation

alone.

Study 2: Examined the individual and combined effects of RE and whey protein

supplementation on skeletal muscle/FFM, muscle strength, physical function, and hormonal

and inflammatory biomarkers related to sarcopenia. Resistance exercise significantly

increased FFM, muscle strength and physical function, and decreased markers of systemic

inflammation compared to non-exercise. Whey protein supplementation increased physical

function (4 m gait speed) and muscle strength [leg press one repetition maximum (1RM)]. No

synergistic effects occurred for any parameter of sarcopenia compared to RE or whey protein

supplementation alone. Furthermore, changes in hormonal and inflammatory markers did not

correlate with changes in skeletal muscle mass, strength, or physical function. Diurnal salivary

cortisol secretion did, however, significantly correlate with multiple parameters of sarcopenia

at baseline.

Study 3: Tested the individual and combined effects of RE and whey protein supplementation on cognitive function and explored mechanisms of action. At baseline, parameters of sarcopenia (muscle strength and physical performance) positively correlated with several domains of cognitive function. Following the intervention, RE and whey protein supplementation alone and combined did not elicit any significant benefits compared to control. However, whey protein supplementation per se elicited within-group improvements in global cognitive function, working memory and executive function. When whey protein supplement groups were pooled, there was also a trend towards a greater increase in globalcognitive function compared to control supplement groups pooled. Resistance exercise alone elicited within-group improvements in multitasking efficiency but worsened processing speed. No significant additive effects of combined intervention were observed compared to either RE or whey protein supplementation alone. Moreover, changes in cognitive function were notcorrelated with changes in any neurobiological, inflammatory or insulin sensitivity marker, nor blood pressure or salivary cortisol indices. In contrast, an association was observed between changes in SMI and episodic memory.
Conclusions: Overall, this body of work supports the use of RE as the primary intervention to mitigate age-related declines in EE and parameters of sarcopenia. Increased dietary protein intake via whey protein supplementation may also be recommended as a safe method for older adults to mitigate age-related declines in muscle strength, physical function and sarcopenic obesity, and aid aspects of cognitive functioning. Finally, data presented in this thesis does not support the need for combined RE and whey protein supplementation to curb sarcopenia or age-related declines in metabolic or cognitive function.

Date of Award	Aug 2021
Original language	English
Awarding Institution	Coventry University University Hospitals Coventry and Warwickshire NHS Trust
Sponsors	Coventry University
Supervisor	Derek Renshaw (Supervisor), John Hattersley (Supervisor) & Michael Duncan (Supervisor)