The increased prevalence of childhood overweight and obesity is not unique to industrialized societies; dramatic increases are occurring in urbanized areas of developing countries. In light of the consensus that obesity is a significant public health concern and that many weight-loss interventions have been unsuccessful in the long term, an exploration of food patterns that are beneficial in the primary prevention of obesity is warranted. The focus of this article is to review the relation between vegetarian diets and obesity, particularly as they relate to childhood obesity. Epidemiologic studies indicate that vegetarian diets are associated with a lower body mass index (BMI) and a lower prevalence of obesity in adults and children. A meta-analysis of adult vegetarian diet studies estimated a reduced weight difference of 7.6 kg for men and 3.3 kg for women, which resulted in a 2-point lower BMI (in kg/m(2)). Similarly, compared with nonvegetarians, vegetarian children are leaner, and their BMI difference becomes greater during adolescence. Studies exploring the risk of overweight and food groups and dietary patterns indicate that a plant-based diet seems to be a sensible approach for the prevention of obesity in children. Plant-based diets are low in energy density and high in complex carbohydrate, fiber, and water, which may increase satiety and resting energy expenditure. Plant-based dietary patterns should be encouraged for optimal health and environmental benefits. Food policies are warranted to support social marketing messages and to reduce the cultural and economic forces that make it difficult to promote plant-based dietary patterns.