American journal of preventive medicine
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The National Academy of Medicine recommends childhood obesity prevention efforts making healthier options the passive choice. This review evaluated the effectiveness of population-level policies and programs from natural experiments for childhood obesity prevention. ⋯ Natural experiments evaluating school-based policies focusing on both the food/beverage and physical activity environments (versus targeting only one) consistently showed improvement in BMI. However, most studies had high risk of bias, highlighting the need for improved methods for evaluation of natural experiments for childhood obesity prevention.