Group motivational interviewing in the 'Small Changes' weight management project: a quasi-experimental trial

Background - Motivational interviewing has been recommended as an effective counselling intervention for weight management with overweight and obese individuals. Nevertheless, there is a paucity of research for the use of motivational interviewing in weight management groups and research in the area often lacks sufficient 'treatment fidelity', failing to accurately report the consistency, style, content and competence of those delivering the intervention. The current study examined the efficacy of the Small Changes weight management programme comparing motivational interviewing in groups to treatment as usual. Methods - Those in the motivational interviewing group intervention received 12 sessions of 2 hours, which comprised 9 group and 3 one to one sessions over 12 months. The motivational interviewing group were treated in a motivational interviewing consistent manner throughout; for example, change talk was identified, evoked and strengthened via specific micro-skills such as open questions, affirmations and reflections. In the treatment as usual group, subjects also received 9 group and 3 one to one sessions over a 12 month period. The treatment as usual group were required to self-select a 'Small Change' at each meeting with the facilitator. All subjects were measured at five time points: baseline, 3, 6, 9 and 12 months, outcome measures included: weight, body mass index, body-fat percentage, waist to hip ratio, number of minutes of daily physical activity, fruit and vegetable consumption and feelings of well-being. A treatment fidelity framework was applied to the motivational interviewing groups' intervention to ensure a consistent, reliable and reproducible approach. Results - After 12 months, improvements were shown for all variables measured in the motivational interviewing groups; only the composite measure of physical and psychological wellbeing improved statistically in the treatment as usual groups, . When comparing approaches: significant differences were found between motivational interviewing and treatment as usual in favour of the motivational interviewing intervention for mean percentage change in weight and body mass index but not for % body fat, waist to hip ratio, fruit and vegetable consumption, feelings of well-being or physical activity levels. The retention rates in the motivational interviewing groups were higher with 64% of subjects returning for the 12 month outcome measures versus 14% in the treatment as usual groups. Conclusions - This study indicates improvements to weight loss outcome measures after 12 months for an intervention implementing motivational interviewing for weight management groups when compared to an existing weight management programme. Future research is needed to establish the empirical basis for the use of motivational interviewing for weight management groups, with heterogeneity of dose and treatment fidelity as essential features. Keywords : Motivational interviewing, treatment fidelity, weight management