Psychological flexibility and the gains of acceptance-based treatment for post-bariatric surgery: six-month follow-up and a test of the underlying model S. Weineland 1 , S. C. Hayes 2 and J. Dahl 1 Research highlights • Bariatric surgery is associated with dramatic weight loss. • Follow-up studies show that many surgery patients continue to struggle with self-stigma, body dissatisfaction and emotional eating. • To date we are aware of only three published randomized controlled trials evaluating psychological interventions in combination with bariatric surgery. • Acceptance and Commitment Therapy (ACT) targets psychological flexibility: acceptance to have difficult feelings and thoughts, while at the same time engaging in vital healthy activities. • The present study shows significant improvements in the ACT group as compared with (TAU) after treatment as usual at a 6-month follow-up and shows that the mechanism of change may be psychological flexibility. • Results from this study indicate the possibility of optimizing bariatric surgery outcomes by adding interventions targeting psychological flexibility. 1 Department of Psychology, University of Uppsala, Uppsala, Sweden; 2 Department of Psychology, University of Nevada, Reno, NV, USA Received 16 February 2012; revised 17 May 2012; accepted 23 May 2012 Address for correspondence: Ms S Weineland, Department of Psychology, University of Uppsala, von Kraemers allé 1, 751 42 Uppsala, Sweden. E-mail: sandra.weineland@psyk.uu.se Summary The current article presents and evaluates an Acceptance and Commitment Therapy (ACT) approach for obesity-related psychological struggles post- bariatric surgery. Some patients who have undergone bariatric surgery report loss of control over eating and distress concerning body figure and shape, which can affect other outcomes such as weight loss and quality of life post surgery. A recent randomized trial (n = 39) evaluating a 6-week treatment package of ACT follow- ing bariatric surgery found large and significant effects as compared with treat- ment as usual (TAU) on eating disordered behaviours, body dissatisfaction, psychological flexibility and quality of life. Though effects were found, questions remain regarding maintenance of outcomes and the process changes related to outcomes. The present study examines both the maintenance of behavioural change at a 6-month follow-up for the original study and the processes that may be involved in the outcomes. ACT led to gains in quality of life (es = 0.88) and body dissatisfaction (es = 0.77), as compared with TAU at follow-up. Both groups improved in eating disordered behaviours (ACT; es = 0.86 and TAU; es = 0.55). A series of multiple mediator tests supported the role of enhanced psychological flexibility in the changes seen in body dissatisfaction, eating disordered behaviour and quality of life. This study provides preliminary support for the ACT treatment model in terms of optimizing bariatric surgery outcomes. Keywords: Acceptance and commitment therapy, bariatric surgery, body dissatisfaction, eating behaviour. clinical obesity doi: 10.1111/j.1758-8111.2012.00041.x 1 © 2012 The Authors Clinical Obesity © 2012 International Association for the Study of Obesity. clinical obesity