Background: People with mental illness often experience unique barriers to healthy eating and physical activity. For these clients, interventions should focus on changes in the immediate environment to change behaviors. The purpose of this project was to implement and evaluate policy changes that would limit calorie intake and increase calorie expenditure of clients receiving mental health services.Context: This intervention was implemented in a rural mental health system in the southeastern United States. Clients live in small group homes, where they are served breakfast, dinner, and a snack, and attend outpatient day treatment programs, where they are served lunch and can purchase snacks from vending machines.Methods: This intervention included institutional policy changes that altered menus and vending machine options and implemented group walking programs. Primary outcome measures were changes in clients' weight at 3 and 6 months after policy implementation.Consequences: At the 3-month follow-up, the median weight loss for overweight/obese clients (n = 45) was 1.4 kg. The 33 overweight/obese clients who were still in the group homes at the 6-month follow-up either maintained or continued to lose weight.Interpretation: Institutional policy changes aimed at improving dietary intake and physical activity levels among clients receiving mental health services can promote weight loss in overweight clients.