At the same time there is more to obesity than "calories in/calories out." A case in point is a recent study tying body mass index (BMI) to pollutants. That investigation suggests that exposure to second-hand smoke and roadway traffic may be linked to increased BMI in children and adolescents. These studies and reports on pollutants and other chemicals contribute to the movement challenging the causes of obesity as simple caloric explanations. We have much more to learn about the complexities concerning excessive weight gain.