1. From the Departments of Nutrition (KZL) and Epidemiology (EH), Harvard School of Public Health, Boston MA; the Center for Childhood and Adolescent Health, Secretary of Health, Mexico City, Mexico (YM); the Hospital Infantil de Mexico “Federico Gomez”, Mexico City, Mexico (JIS); the School of Natural Sciences, Universidad Autónoma de Queretero, Queretero, Mexico (JLR)