“We all agree — and despair — that obesity is on the rise. America has been getting fatter for the past century, and the problem has worsened over the past 35 years. We also all know the obvious explanations. Who would discount the role of new food-marketing practices, like super-sizing or pushing soda sweetened with corn syrup? Or the decrease — even elimination — of physical activity in school and in adult life? An important new paper, though, cautions us to be skeptical that corn syrup and sitting around are the only factors that matter for understanding the obesity epidemic.”