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Title: Influence of body composition, metabolism and physical activity on mechanisms controlling energy intake
Author: Hopkins, Mark
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2013
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Background: Current models of appetite control embody the view that tonic and episodic inhibitory signals modulate a constant and recurring drive to eat, but the source of this excitatory drive has been poorly defined. A motivational drive arising from energy needs would appear logical, but the influence of energy expenditure on energy intake remains unclear. Furthermore, while changes in eating behaviour and body composition following acute and chronic exercise are highly variable, a greater understanding of the compensatory mechanisms that mediate this heterogeneity is needed. Methods: A multi-level experimental platform was used in which body composition, metabolism and eating behaviour were measured concurrently in overweight and obese individuals in response to either an acute bout of aerobic exercise, or 12 weeks of supervised aerobic exercise training. This approach allowed for the disclosure of any interdependent relationships between physiological and behavioural components of energy balance. Results: The key findings of this thesis are novel and demonstrated that: • Fat-free mass is a physiological source of hunger that drives day-to-day food intake at a level proportional to basal energy requirements. This homeostatic signal of energy demand was apparent under sedentary conditions, and during exercise-induced weight loss. In contrast, fat mass did not appear to exert a major influence on hunger or food intake under sedentary conditions. • Following 12 weeks of aerobic exercise, marked individual variability existed in exercise-induced weight loss. • While there was no mean change in food intake following 12 weeks of aerobic exercise, fasting hunger increased significantly following the exercise intervention. However, this increase in orexigenic drive was off-set by a parallel increase in meal-related satiety. • Some individuals experienced a greater than expected decline in resting metabolic rate following the 12 week exercise intervention (that could not be explained by changes in body composition). Importantly, these individuals also demonstrated a concomitant increase in food intake following the intervention. • Leptin was found to play a key role in co-ordinating the physiological and behavioural responses to exercise-induced weight loss, with a decline in fasting leptin (independent of fat mass) associated with a greater than expected decline in resting metabolic rate, a smaller increase in resting fat oxidation, an increase in daily hunger, and an increased liking for high fat foods following the 12 week exercise intervention. Conclusions: An important role for fat-free mass in the control of appetite was identified. Furthermore, the impact of exercise on appetite control and body weight regulation was found to be mediated through a cluster of inter-related physiological and behavioural pathways, with leptin potentially acting to co-ordinate these adaptive responses.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available