Date of Award


Degree Type


Degree Name

Doctor of Philosophy in Psychology



First Advisor

Andrea Paiva


In the last decade, the prevalence of obesity has increased significantly in populations worldwide. It is well established that overweight and obesity are associated with a host of deleterious health consequences. Standard Behavioral Therapy (SBT) for weight loss has been demonstrated to yield only modest outcomes with poor long-term maintenance. Therefore, efforts must be made to improve upon what is currently considered to be best practices in weight loss interventions, especially with a goal of improving retention and long-term maintenance. Acceptance and Commitment Therapy (ACT) is a behavioral and cognitive intervention that implements both acceptance and mindfulness processes, and commitment and behavior change processes with the purpose of increasing psychological flexibility to allow an individual to live a value-driven life. To date little is known about the effects of improving one’s consistency of values regarding weight loss and weight loss maintenance. The purpose of this secondary data analysis of a randomized controlled trial (N=162) aimed to model weight and values scores during 12 months of intervention and 12 months of follow-up and to conduct a mediation analysis to identify if, and how much, values scores mediated change in weight over time. Longitudinal modeling demonstrated the SBT arm exhibited a slightly larger decrease in weight during the study invention, but also exhibited a larger rebound in weight gain post-intervention compared to the ACT arm (p=0.0277). The longitudinal modeling of participant values suggests that both arms exhibited an increase in the value score throughout the study intervention; however, after the study intervention, the SBT arm saw a drop in the value score whereas the ACT arm appeared to maintain the gain in value score on average (p=0.0003). Finally, the mediation analysis suggests that change in value score at 18 months partially mediates (50.7%) between study treatment arm and weight loss at 24 months. Future research needs to replicate this finding, and to examine the mechanisms of change (specifically values clarity) with more sophisticated statistical analyses and larger sample sizes, to further understand the proposed mechanisms of change contribution.



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