Abstract

This thesis aims to explore the basic behavioural science guiding the design and development of nutrition-focused behavioural interventions adjunct to metabolic bariatric surgery (MBS). It comprises three systematic reviews to; 1) evaluate the quality of intervention reporting; 2) identify the potentially active content of interventions; and 3) explore perceived barriers and enablers to modifying post-operative dietary behaviours.

In Study one, the Template for Intervention Description and Replication (TIDieR) checklist was applied to evaluate the completeness of intervention reporting. In Study two, intervention materials were coded using the Behaviour Change Technique Taxonomy version 1 (BCTTv1). In addition to descriptive methods, effect size calculations were used to assess the impact of the interventions on weight outcomes. In Study three, data reporting barriers and enablers to modifying diet after MBS were analysed using the Theoretical Domains Framework (TDF). Barriers/enablers were mapped to BCTs to identify potential intervention strategies.

Among the 22 included interventions, none of them completely reported all intervention descriptors in the TIDieR checklist, with an average of 6.6/12 items being fully reported. The areas where reporting required improvement were; providing adequate details of the materials and procedures of the interventions; intervention personalisation; and modifications during the study. Common BCTs reported in interventions included: Instruction on how to perform a behaviour; Self-monitoring of behaviour; Goal setting (behaviour); Problem solving; Social support (unspecified); and Action planning. The BCTs that were only found in the most efficacious interventions (Monitoring of behaviour by others without feedback and Information about antecedents) were not among the most frequent techniques. Key factors influencing post-operative dietary behaviour change were in the categories of Environmental Context and Resources; Behavioural Regulation; Emotions; Beliefs about Consequences; and Social Influences. Potential strategies (BCTs) to support postoperative dietary behaviour change are in line with our findings in study two.

The poor quality of intervention reporting in the current literature limits the potential for evidence synthesis across studies. Addressing barriers to post-operative dietary change, ensuring transparent intervention reporting through behavioural science tools, and frameworks will contribute to the development of interventions that not only engage and mobilise patients towards positive behaviour change but also produce replicable evidence to inform clinical practice.