Abstract
The two most common forms of obesity management are currently behavioural and surgical interventions. This research aimed to explore the impact of behavioural and surgical interventions on weight loss outcome and to assess the mechanisms of change involved in this process with a focus on social cognitions, adaptive and maladaptive eating. The thesis consists of three studies which were designed using the Health Action Process Approach model as a theoretical framework. For study one a longitudinal design was adopted and data were collected from individuals undergoing behavioural and surgical weight loss interventions pre-treatment, at three months and six months post-treatment. Part one investigated the differences in social-cognitions between individuals undergoing behavioural and surgical interventions and parts two to four investigated predictors of adaptive and maladaptive eating and their role in weight loss. Building on this, study two used a qualitative design to investigate the long-term experience of patients undergoing surgery for weight loss with a particular focus on eating behaviour. Finally, study three was a Randomised Controlled Trial of a planning prompt to enhance weight reduction in individuals undergoing surgical weight loss interventions. Overall results showed that obese participants having either surgery or behavioural interventions vary along a number of different dimensions and that the roles of eating behaviours for the prediction of weight loss differ in these two populations. Not only does the mode of management influence the success of patient outcomes, but also the changes in the mechanisms necessary to bring about these outcomes. Based on the results of the studies it would seem that when trying to understand weight loss, a single model such as the HAPA although useful for study design, cannot be applied to all populations and that not only do the weightings given to different components vary between populations but also the associations between components and outcomes.