Background
It was proposed over 60 years ago that “the differences between the intakes of food must originate in differences in the expenditure of energy” (Edholm et al., 1955). It was also proposed that a ‘U’ shaped function described the relationship between physical activity (PA) energy expenditure (EE) and dietary intake (Mayer et al., 1956); this relationship also involved body mass. These relationships served as the basis for the studies conducted for this thesis. The main objective was to examine the associations among free-living sedentary and active behaviours, adiposity and appetite control. The investigation was conducted within an energy balance framework. The main focus of the thesis was to extend understanding of the interaction between PA, sedentary behaviour (SB), adiposity and appetite.
Methods
The methodology was based on measurements of body composition together with anthropometric, physiological, behavioural and psychological variables and involved a combination of cross-sectional and medium-term (12-weeks) intervention studies. The thesis used state-of-the-art methodology for measuring free-living activity and aimed to detect a measure of SB based on both posture and activity intensity.
Results
Study 1 - SB was positively associated with adiposity and moderate-to-vigorous physical activity (MVPA) was negatively associated with adiposity.
Study 2 - A procedure was developed to integrate data on two dimensions of free-living SB (posture and activity intensity) using two validated activity monitors.
Study 3 - Posture alone (as a marker of SB) is not a good indicator of the tendency to accumulate fat mass (FM).
Study 4 - Total EE and the metabolic contributors to total EE (fat-free mass (FFM) and resting metabolic rate (RMR)) were associated with subjective appetite sensations and EI, and provisionally can be regarded as drivers of appetite.
Study 5 - The 12-week exercise intervention resulted in a significant (compensatory) increase in EI, however, there was no change in non-exercise physical activity (NEPA).
Study 6 - Diet induced weight loss (mainly FM loss) did not lead to a compensatory reduction in PA or increase in SB.
Conclusions
These studies have extended the understanding of the associations among PA, SB, adiposity and appetite control. The outcomes of the studies have contributed to a theoretical framework for understanding the interactions between physiological and behavioural variables that contribute to energy balance and body mass (adiposity) regulation under realistic conditions. It could be deduced that a combination of increased EE (through exercise) and reduced EI are likely to produce greater weight loss and more favourable changes in body composition than either exercise or diet alone.
