A feasibility randomised controlled trial of a motivational interviewing-based intervention for weight loss maintenance in adults

Background: Obesity has significant health and NHS cost implications. Relatively small reductions in weight have clinically important benefits, but long-term weight loss maintenance (WLM) is challenging. Behaviour change interventions have been identified as key for WLM. Motivation is crucial to supporting behaviour change, and motivational interviewing (MI) has been identified as a successful approach to changing health behaviours. The study was designed as an adequately powered, pragmatic randomised controlled trial (RCT); however, owing to recruitment issues, the study became a feasibility trial. Objectives: To assess recruitment, retention, feasibility, acceptability, compliance and delivery of a 12-month intervention to support WLM. Secondary objectives were to assess the impact of the intervention on body mass index (BMI) and other secondary outcomes. Design: Three-arm individually randomised controlled trial comprising an intensive arm, a less intensive arm and a control arm. Setting: Community setting in South Wales and the East Midlands. Participants: Individuals aged 18–70 years with a current or previous BMI of ≥ 30 kg/m2 who could provide evidence of at least 5% weight loss during the previous 12 months. Intervention: Participants received individually tailored MI, which included planning and self-monitoring. The intensive arm received six face-to-face sessions followed by nine telephone sessions. The less intensive arm received two face-to-face sessions followed by two telephone sessions. The control arm received a leaflet advising them on healthy lifestyle. Main outcome measures: Feasibility outcomes included numbers recruited, retention and adherence. The primary effectiveness outcome was BMI at 12 months post randomisation. Secondary outcomes included waist circumference, waist-to-hip ratio, physical activity, proportion maintaining weight loss, diet, quality of life, health service resource usage, binge eating and well-being. A process evaluation assessed intervention delivery, adherence, and participants’ and practitioners’ views. Economic analysis aimed to assess cost-effectiveness in terms of quality-adjusted life-years (QALYs). Results: A total of 170 participants were randomised. Retention was good (84%) and adherence was excellent (intensive, 83%; less intensive, 91%). The between-group difference in mean BMI indicated the intensive arm had BMIs 1.0 kg/m2 lower than the controls [95% confidence interval (CI) –2.2 kg/m2 to 0.2 kg/m2]. Similarly, a potential difference was found in weight (average difference of 2.8 kg, 95% CI –6.1 kg to 0.5 kg). The intensive arm had odds of maintaining on average 43% [odds ratio(OR) 1.4, 95% CI 0.6 to 3.5] higher than controls. None of these findings were statistically significant. Further analyses controlling for level of adherence indicated that average BMI was 1.2 kg/m2 lower in the intensive arm than the control arm (95% CI –2.5 kg/m2 to 0.0 kg/m2). The intensive intervention led to a statistically significant difference in weight (mean –3.7 kg, 95% CI –7.1 kg to –0.3 kg). The other secondary outcomes showed limited evidence of differences between groups. The intervention was delivered as planned, and both practitioners and participants were positive about the intervention and its impact. Although not powered to assess cost-effectiveness, results of this feasibility study suggest that neither intervention as currently delivered is likely to be cost-effective in routine practice. Conclusion: This is the first trial of an intervention for WLM in the UK, the intervention is feasible and acceptable, and retention and adherence were high. The main effectiveness outcome showed a promising mean difference in the intensive arm. Owing to the small sample size, we are limited in the conclusions we can draw. However, findings suggest that the intensive intervention may facilitate long-term weight maintenance and, therefore, further testing in an effectiveness trial may be indicated. Research examining WLM is in its infancy, further research is needed to develop our understanding of WLM and to expand theory to inform the development of interventions to be tested in rigorously designed RCTs with cost-effectiveness assessed. Trial registration: Current Controlled Trials ISRCTN35774128. Funding: This project was funded by the National Institute for Health Research Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 19, No. 50. See the NIHR Journals Library website for further project information