The overarching purpose of this PhD research program was to explore ways in which behaviour change theory and digital health following bariatric surgery can be used to inform future interventions aimed at improving the health outcomes of bariatric patients. This is important as solutions are needed for individuals who have undergone bariatric surgery to help support weight maintenance postoperatively. The thesis progressed from identifying target behaviours to identifying theoretical domains and behaviour change techniques and, finally, implementing an intervention that could be evaluated in a non-randomised feasibility study. Six main aims drove this PhD program of research to achieve the overarching purpose.

Aim One identified the target behaviours that need to be performed after bariatric surgery, the effect of behavioural non-adherence on weight regain, and barriers to behaviour change. Aim Two was to choose a theoretical framework to guide the PhD research program. Aim Three identified current intervention components in the literature by determining behaviour change theories and techniques used to inform nutrition interventions for adults undergoing bariatric surgery. Aim Four explored patient barriers to and determined current technology use for accessing bariatric surgery services and health information and explored the acceptability of digital health in bariatric surgery using the theoretical domains framework. Aim Five identified the various modalities of digital health and evaluated the effectiveness of digital health on bariatric surgery postoperative outcomes. Aim Six assessed the feasibility, acceptability, cost, and potential effect on weight of a digital health solution in bariatric surgery with potential for scale-up.

The PhD research program adopted a robust methodology, including two comprehensive systematic literature reviews, a mixed-methods study, and a non-randomised feasibility study, all aimed at gaining insights for the development of digital health interventions targeted at improving the health outcomes of bariatric patients. The thesis followed a multi-stage approach guided by the French et al. (2012) model (French model) and the theoretical domains framework, ensuring a thorough process for developing and evaluating a digital health intervention in bariatric surgery. [...]