A peer-reviewed study published this week in the Proceedings of the National Academy of Sciences concludes that overconsumption of ultra-processed, calorie-dense foods is the dominant driver of obesity in economically developed countries. The researchers found that dietary patterns, rather than physical inactivity, account for the sharp rise in body-mass index observed during the past several decades. The paper reports that exercise alone makes only a modest contribution to weight control, challenging public-health campaigns that focus primarily on boosting physical activity. Instead, the authors urge policymakers to prioritize measures that reduce access to and demand for ultra-processed foods, such as reformulating products, improving food labeling and adjusting fiscal incentives. If adopted, the researchers argue, these interventions could slow or reverse obesity trends and cut related health-care costs, which currently total hundreds of billions of dollars annually in the United States and other high-income nations.