BACKGROUND: The worksite represents a promising venue in which to address the issue of obesity.

DESIGN: Pair-matched, cluster-RCT. Data were collected from 2005 to 2008 and analyzed in 2008.

SETTING/PARTICIPANTS: A random sample of 806 employees was selected to represent the workforce of six hospitals in central Massachusetts.

INTERVENTION: The 2-year ecologic intervention sought to prevent weight gain through changes in worksite weight-related norms using strategies targeted at the organization, interpersonal environment, and employees.

MAIN OUTCOME MEASURES: The primary outcome was change in BMI at the 12- and 24-month follow-ups. Change in perceptions of organizational commitment to employee health and normative coworker behaviors were secondary outcomes.

RESULTS: There was no impact of the intervention on change in BMI from baseline to 12 (beta=0.272; 95% CI=-0.271, 0.782) or 24 months (beta=0.276; 95% CI=-0.338, 0.890) in intention-to-treat analysis. When intervention exposure (scale=0 to 100) was used as the independent variable, there was a decrease of 0.012 BMI units (95% CI=-0.025, 0.001) for each unit increase in intervention participation at the 24-month follow-up. Employees in intervention sites reported significantly greater improvements in perceptions of organizational commitment to employee health at 12 and 24 months compared to control sites, but there was no impact on perceptions of normative coworker behaviors.

CONCLUSIONS: The intervention had a dose-response relationship with BMI, with positive effects proportional to extent of participation. Although the intervention was able to change organizational perceptions, successfully improving changes in actual and perceived social norms may be needed to achieve population-level impact in complex worksite organizations. All rights reserved.