Does Motivational Interviewing Improve Behavioral Weight Loss Outcomes for Obesity?

Although behavioural weight loss programs (BWLP) are typically the first line of treatment for obesity, they are often plagued by high attrition rates and poor adherence. Studies evaluating the benefit of adding motivational interviewing (MI) to BWLPs have yielded mixed findings. The main purpose of this randomized controlled trial was to assess the efficacy of adding MI to a BWLP on weight loss and adherence outcomes among 135 overweight and obese individuals enrolled in a 12-week (24 session) BWLP. This study used a randomized, controlled, longitudinal, between-subjects design to investigate the effects of a two-session MI intervention on weight loss in participants enrolled in a BWLP. Patients received either two 45-60 minute MI interventions or two 45-60 minute attention control interviews. The control group interview consisted of questions ascertaining weight history, diet history, dietary awareness and physical activity. Questions for the control group focused primarily on assessment of past behaviour whereas questions for the MI group focused on enhancing motivation by exploring and resolving ambivalence. Weight was measured at baseline, end of the BWLP, and 6 months following BWLP completion. Program adherence (measured as number of BWLP sessions attended out of 24) was assessed as a secondary dependent measure. Importance, readiness, and confidence for weight change were assessed at baseline and then immediately following each interview (either MI or control). In addition, several other secondary outcome measures were assessed at baseline, end of the BWLP, 1 month follow-up, and 6 month follow-up. Research personnel informed all BWLP participants about the study at the initial BWLP group intake assessments, which occurred just prior to the commencement of the formal BWLP. Individuals who expressed interest in participating were contacted by phone by a research assistant and screened for eligibility. If eligible, an appointment was made for the first MI/control session which was scheduled within the first two weeks of the BWLP. Randomization occurred immediately prior to this interview. Participants were then contacted during the 10th week of the BWLP to schedule a second MI/control session, which occurred approximately during the 12th week of the program. Participants were all contacted several weeks following program completion to schedule the one-month follow-up assessment. Finally, all participants were contacted approximately five months following program completion in order to schedule the six-month follow-up assessment. Sessions were tape recorded for all participants for quality assurance purposes. A subset of tapes were used to assess for treatment integrity.