Functional Imagery Training Versus Motivational Interviewing for Weight Loss: a Randomised Controlled Trial of Brief Individual Interventions for Overweight and Obesity

Objective: Functional Imagery Training (FIT) is a new brief motivational intervention based on the Elaborated Intrusion theory of desire. FIT trains the habitual use of personalised, affective, goal-directed mental imagery to plan behaviours, anticipate obstacles, and mentally try out solutions from previous successes. It is delivered in the client-centred style of Motivational Interviewing (MI). We tested the impact of FIT on weight loss, compared with time- and contact-matched MI.

Design: We recruited 141 adults with BMI (kg/m²) ≥25, via a community newspaper, to a single-centre randomised controlled trial. Participants were allocated to one of two active interventions: FIT or MI. Primary data collection and analyses were conducted by researchers blind to interventions. All participants received two sessions of their allocated intervention; the first face-to-face (1 h), the second by phone (maximum 45 min). Booster calls of up to 15 min were provided every 2 weeks for 3 months, then once-monthly until 6 months. Maximum contact time was 4 h of individual consultation. Participants were assessed at Baseline, at the end of the intervention phase (6 months), and again 12 months post-baseline.

Main Outcome Measures: Weight (kg) and waist circumference (WC, cm) reductions at 6 and 12 months.

Results: FIT participants (N = 59) lost 4.11 kg and 7.02 cm of WC, compared to .74 kg and 2.72 cm in the MI group (N = 55) at 6 months (weight mean difference (WMD) = 3.37 kg, p < .001, 95% CI [-5.2, -2.1], waist-circumference mean difference (WCMD) = 4.3 cm, p < .001, 95% CI [-6.3,-2.6]). Between-group differences were maintained and increased at month 12: FIT participants lost 6.44 kg (W) and 9.1 cm (WC) compared to the MI who lost .67 kg and 2.46 cm (WMD = 5.77 kg, p < .001, 95% CI [-7.5, -4.4], WCMD = 6.64 cm, p < .001, 95% CI [-7.5, -4.4]).

Conclusion: FIT is a theoretically informed motivational intervention which offers substantial benefits for weight loss and maintenance of weight reduction, compared with MI alone, despite including no lifestyle education or advice.