Mechanisms that explain behavior change within web-based lifestyle interventions are not well-studied. This secondary analysis explores whether the effects of the DUET web-based lifestyle intervention on diet, physical activity, and/or adiposity are mediated through changes in self-efficacy, social support, and perceived barriers (key constructs of social cognitive theory). Data on mediators, diet quality, caloric intake, moderate-to-vigorous physical activity (MVPA), weight, and waist circumference (WC) were analyzed from 112 cancer survivors and their partners enrolled in the DUET intervention. Mediation analyses were performed using Mplus to execute regression analyses and determine associations. Mediation analyses supported an effect of the intervention on caloric intake (-3.52, 95% CI [-8.08 to -0.84]), weight (-1.60, CI [-3.84 to -0.47]), and WC (-0.83, CI [-1.77 to -0.18]), interpreting these negative associations as intervention induced reductions in dietary barriers. Higher social support was significantly and positively associated with, but not a mediator for, improvements in self-reported and accelerometry-measured MVPA (b = 0.69, CI [0.19, 1.24]) and (b = 0.55, CI [0.15, 1.00]), respectively. Self-efficacy did not appear to mediate the intervention's effects. Findings suggest that the effects of the DUET intervention on diet and adiposity stem from reducing perceived barriers to a healthful, low-calorie diet.
Keywords: barriers; cancer survivors; diet; dyads; exercise; internet; self-efficacy; social support.