Stage-based analysis of an adaptive worksite intervention trial for diabetes prevention.

Objective: Stage-based models of change posit stage specific factors to promote motivation and intention formation for those not ready to change and volitional action strategies for others. The impact of two interventions on energy restriction and weight change among adults with prediabetes (n = 190) was examined by baseline stage.

Methods: Stage classification included: Pre-intenders had no intention to change; Intenders set an intention but were not acting; and Actors reported eating a low-fat diet at baseline. Intervention impact on intention formation, planning, self-efficacy, energy intake, and weight change was evaluated. Structural equation modeling identified mechanisms of change.

Results: At baseline, Pre-intenders (28.3 %) and Actors (41.7 %) significantly differed in action self-efficacy, planning, and energy intake. Post-intervention, 91.7 % of the sample remained Actors or progressed in stage placement; intention to consume a low-fat diet increased for Pre-intenders. An increase in action self-efficacy strengthened intention formation for Intenders/Actors. Model fit for post-intentional factors was unsatisfactory, but dietary planning may promote energy restriction.

Conclusions: The lifestyle interventions promoted stage progression. Whether post-intentional mechanisms of change differ for Pre-intenders compared to Intenders/Actors requires further research.

Practice Implications: Classifying participants by intention and tailoring interventions to stage may promote greater intention formation and reduction in energy intake.