The impact of the interventionist–participant relationship on treatment adherence and weight loss

Little is known about the impact of the relationship built between interventionists and their participants on weight loss. Our objective is to determine whether stronger early (i.e., 4 weeks) participant-interventionist bond is associated with significantly greater weight loss success and treatment adherence. Three hundred and ninety-eight participants received an online group behavioral weight control program over 18 months. Weight was measured objectively at baseline and at 6 and 18 months. At 4 weeks, participants completed the Working Alliance Inventory (WAI) bonding subscale, which measures the collaborative bond with the interventionist. Adherence (i.e., session attendance and online self-monitoring diary completion) was recorded by the interventionists. Participant-interventionist bond at 4 weeks was significantly associated with weight loss at 6 months (t(322) = -2.14, p = .03) but not at 18 months (t(290) = 0.53, p = .60). The model indicated that participant-interventionist bond at 4 weeks was a significant predictor of adherence at 6 months (b = .063, standard error [SE] = .30, p = .04), and 6 month adherence was a significant predictor of weight loss at 6 months (b = -.594, SE = .049, p < .0001). The indirect effect of the WAI-Bond subscale was significant (b = -.037, p = .03, 95% confidence interval: -.074, -.002) and accounted for 54% of the total effect of participant-interventionist bond on weight loss. However, the total weight loss explained by WAI-Bond subscale was small (0.04 kg). Participant-interventionist bond between participant and interventionist is an early predictor of treatment adherence and weight loss success at 6 months; however, the degree of weight loss explained by participant-interventionist bond is small and was not maintained at 18 months.