Self-efficacy as a predictor of weight change and behavior change in the PREMIER trial

Abstract

Objectives: Determine whether self-efficacy independently predicted weight loss in a behavioral intervention and explore factors that influence the path between self-efficacy and weight change.

Design: Secondary analysis of the PREMIER trial, a randomized controlled trial testing effects of lifestyle interventions on blood pressure.

Setting: Four academic medical centers.

Participants: PREMIER recruited adults (n = 810) with pre-hypertension/stage 1 hypertension, not currently receiving medication. This analysis excluded participants in the control arm, resulting in n = 537.

Interventions: Participants were randomly assigned to 1 of 3 groups: advice only, established lifestyle recommendations, or established lifestyle recommendations plus Dietary Approaches to Stop Hypertension dietary pattern.

Main outcome measures: Self-efficacy (dietary self-efficacy [DSE], exercise self-efficacy [ESE]), dietary intake, fitness.

Analysis: Pearson correlations, 1-way analysis of variance, mediation analyses.

Results: Despite an overall decrease in DSE/ESE, change in DSE/ESE significantly predicted weight change at 6 (β = -.21, P < .01; β = -.19, P < .01, respectively) and 18 months (β = -.19, P < .01; β = -.35, P < .01). Change in percent calories from fat partially mediated the DSE/weight change relationship at 6 months. Change in fitness partially mediated the ESE/weight change relationship at 18 months.

Conclusions and implications: Changes in DSE/ESE were not associated with behavior change as hypothesized. Additional research is needed to identify mediators between self-efficacy and adoption of behaviors that influence weight loss.

Figure 1

Differences in weight loss between self-efficacy (SE) tertiles at 6 and 18 months. Groups formed by creating tertiles of change in self-efficacy scores from baseline to follow-up. Tertiles represent greatest increase in SE, no significant change in SE, and greatest decrease in SE. *Significantly different from greatest decrease group at P < .01 level.

Figure 2

Mediation analysis for change in percent dietary fat intake at 6 months. *P < .05; **P < .001. Statistical test: Baron and Kenny mediation analysis. Step 1 β = −.21; Step 2 β = −.07; Step 3 β = .31; Step 4 β = −.18.

Figure 3

Mediation analysis for change in cardiorespiratory fitness at 18 months. *P < .05; **P < .001. Statistical test: Baron and Kenny mediation analysis. Step 1 β = −.35; Step 2 β = −.17; Step 3 β = −.59; Step 4 β = −.31.