Insufficient physical activity and sedentary behavior are both associated with higher risk of chronic disease and death. However, the long-term benefits of interventions to increase physical activity and reduce sitting time are unknown as randomized controlled trials are often infeasible or costly. Using data collected from 6,377 participants in the Australian Diabetes, Obesity and Lifestyle Study, investigators simulated specific health interventions. The scenarios involved increasing everyone’s leisure-time physical activity, decreasing their time watching TV, or both. Investigators compared the risk of death under each intervention. Increasing leisure-time physical activities to 150 to 300 minutes/week reduced the risk of death over 13 years by 8%, and by 17% if increasing it to more than 300 minutes/week. However, there was limited gain from keeping TV time under two hours/day. The findings were based on self-reported physical activity levels and TV time. Future research will benefit from integrating data of device-assessed physical activity and sedentary behavior.