| Summary: | Although the majority of obese and overweight individuals successfully lose weight only a minority maintain weight loss in the long term. This thesis, through a mixed model methods approach, examined the factors which reinforced healthy behavior change in a group of obese and overweight individuals and assessed the factors which underlined sustained behavior change in the minority of individuals who successfully maintained at least 10% of their initial weight loss. In particular, the thesis focuses on the role of life events in triggering behaviour change and the impact of sustaining conditions in maintaining this change in the long term. Study 1 was a quantitative study. Members of a commercial weight loss program (N= 1093) were invited to participate in the study through an online advertisement. The aim of the study was to examine participants' different weight patterns, based on their weight history, and to assess whether these patterns were explained by participants' weight and demographic characteristics. The results showed that weight histories could be categorized into 5 independent patterns which were: a) weight cycling with overall increase, b) weight cycling with initial weight stability, c) weight cycling with return to baseline, d) weight loss and e) gradual gain. Concerning participants' demographic and weight characteristics, results also revealed significant .differences between the different weight patterns. In addition, obese and overweight individuals indicated significant differences in their weight histories. Based on their weight histories, and in particular, their percentage of weight loss, participants could be also categorized into those individuals who regained some or all of their weight loss (unsuccessful participants; N= 592) and those who managed to maintain at least 10% of their initial weight loss and which they maintained for a minimum of one year (successful participants; TV = 431). Study 2 then focused on these two groups and aimed to examine the role of life events and sustaining conditions in behavior change and behavior maintenance. Variables such as participants' health status and experiences with consultants were also included in the analysis. Results revealed significant differences between the two groups with successful participants indicating more life events, less benefits from their unhealthy behavior, more choice over their healthy behavior and more psychological beliefs about causality which were related to their behavioral solutions. Also, successful participants were more positive concerning their health status and experiences with their consultants. Study 3 applied a within subjects design which aimed to examine the differences within the successful group between Time 1 (Their heaviest) and Time 2 (sustained weight loss) in regards to their health status and sustaining conditions of disruption of function, reduction choice and solutions for their increased weight. The results showed that maintaining weight loss was linked to an improved health status, more choice and perceived benefits over the healthy behavior and an endorsement of an improved and healthier lifestyle. Study 4, using a qualitative approach, aimed to further explore whether maintenance of behavior was related not only to the sustaining mechanisms but also to a shift in identity and perception of self. 10 successful individuals were invited to participate. Using IPA results indicated that weight loss maintenance is related to an identity shift from a previously restrained individual towards a liberated person who tends to redefine themselves based on new qualities apart from their weight. Overall, this thesis indicates that the minority of individuals who are finally successful in losing and maintaining weight loss are more likely to experience some life events central to their goals and identity. These events enhance maintenance when they are accompanied by sustaining mechanisms and by a shift in mental representations about their self.
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