Social Support and Perceived Dietary Barriers Mediate Weight Loss in the AMPLIFY Web-Based Diet Intervention

Web-based interventions that promote healthy diet and weight loss among cancer survivors are growing, but theoretical constructs driving their success remain unclear.

This study explores whether Social Cognitive Theory (SCT) constructs (self-efficacy, social support, perceived barriers) mediate the effects of the AMPLIFY-Diet intervention on energy intake, diet quality, and body weight.

This mediation analysis used data from the AMPLIFY-Diet randomized controlled trial (RCT).

Data collected from March 2020 to March 2024 at baseline, 3 months, and 6 months were analyzed from 346 overweight-or-obese cancer survivors enrolled nationwide.

Cancer survivors received a serialized, theoretically-grounded, 24-week, web-based intervention to improve diet quality and weight loss.

Energy intake and diet quality were measured using two non-consecutive 24-hour dietary recalls, and body weight was measured using digital scales at baseline and 6 months. SCT mediators were assessed using self-reported instruments at baseline, 3 months, and 6 months.

Mediation analyses were conducted to estimate indirect effects.

At 3-months, the effect of the AMPLIFY-Diet intervention on weight was significantly mediated through improvements in social support from baseline (unstandardized indirect effect estimate=-0.42 (SE=0.21); 95% CI [-0.894, -0.084]); whereas, at 6-months, the effect was significantly mediated through reductions in perceived dietary barriers from baseline (unstandardized indirect effect estimate=-0.45 (SE=0.21); 95% CI [-0.928,-0.103]). Self-efficacy, social support, and perceived dietary barriers did not emerge as significant mediators for energy intake or diet quality models.

Findings suggest that the AMPLIFY-Diet intervention achieved weight loss among cancer survivors through time-dependent mechanisms, improving social support earlier in the intervention and reducing perceived dietary barriers later on. However, these constructs did not explain changes in models for dietary intake. Future web-based dietary interventions should measure and examine additional theoretical constructs to better understand the mechanisms underlying dietary change.