H1: The increase in body mass index between baseline and two year follow-up among intervention worksites will be lower than that among control worksites, such that the differential change will be negative on average.

Our overall objective is to develop and evaluate an intervention that will maintain or decrease body mass index; specifically, we will recruit and randomize 30 worksites to a two year intervention in which we will:

• Influence the worksite environment, including policies and procedures, by increasing worksite access to healthy foods and physical activity opportunities
• Promote individual behavior change, through increasing awareness of energy balance; building a physical activity intervention that will promote increased levels of energy expenditure through the combination of increased daily physical activity and regular, structured exercise; and building a dietary intervention that will promote decreased calorie intake.

Our primary aim is to:

1) Evaluate the effectiveness of the intervention in reducing or maintaining body mass index in a randomized controlled trial of worksites.

Our secondary aims are to:

1. Assess changes in worksite environment in access to healthy foods and physical activity opportunities attributable to the intervention
2. Assess changes in individual level physical activity and energy intake attributable to the intervention
3. Assess the changes in sequalae of weight loss including biomarkers of metabolic effects, and weight loss quality of life and symptom measures; and
4. Estimate the cost-effectiveness of the intervention in controlling weight.

Inclusion Criteria:

• Employees of the enrolled worksite who are 18 years or older and work at the company at least 50% FTE (20 hrs per week)

Exclusion Criteria:

• Any employees of the enrolled worksite who are interns or seasonal workers or employees who work less than 50% FTE (20 hrs per week)