Walter C Willett1, David S Ludwig1. 1. From the Departments of Nutrition (W.C.W., D.S.L.) and Epidemiology (W.C.W.), Harvard T.H. Chan School of Public Health; Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School (W.C.W.); the Department of Pediatrics, Harvard Medical School (D.S.L.); and the New Balance Foundation Obesity Prevention Center, Boston Children's Hospital (D.S.L.) - all in Boston.