Appetite regulation and lean mass: considerations in people with a spinal cord injury

People with a spinal cord injury (SCI) experience substantial changes in body composition, including increased adiposity and reduced fat-free mass. These changes augment the risk of obesity and related co-morbidities such as cardiovascular disease and type 2 diabetes. However, little is known about how chronic SCI influences appetite regulation, eating behaviours and obesity risk. Further, the optimal method(s) for maximising skeletal muscle mass (SMM) in the paralysed limbs of people with SCI, and the associated cardiometabolic benefits, are not established.

Chapter 3 of this thesis identified no differences in postprandial appetite-related hormone responses (peptide YY, glucagon-like peptide-1, and acylated ghrelin) to an isoenergetic preload between people with versus without SCI (matched for age, sex, and BMI). However, participants with SCI experienced elevated perceptions of postprandial satiety compared to the group without SCI. This may have been due to the group with SCI consuming a relatively larger test meal, given that energy requirements are typically lower in people with, compared to without, SCI. Accordingly, findings from Chapter 4 revealed no differences in postprandial appetite perceptions between people with versus without SCI following a meal standardised for resting metabolic rate (RMR). Food reward for sweet foods was greater in people with SCI, compared to the group without SCI, in fed and hungry states. These data imply that reward-related influences on eating behaviour more likely underpin obesity risk in this clinical population, rather than homeostatic factors.

Chapter 5 sought to appraise interventions (exercise and non-exercise) aimed at increasing SMM in the paralysed limbs of people with chronic, motor complete SCI. Neuromuscular electrical stimulation-based resistance training (NMES-RT) demonstrated the greatest efficacy in this population. Chapter 6 examined the augmentative effects of NMES-RT with (PRO), versus without (CON), daily protein supplementation on body composition and cardiometabolic markers. NMES-RT increased leg and thigh lean mass, but protein supplementation did not potentiate effects. These preliminary findings require additional scrutiny through fully powered efficacy studies.