1. Instituto de Investigacion Nutricional, Apartado 55, Miraflores (Lima), Peru, Department of Agronomy, Purdue University, W. Lafayette, Indiana 47906 and Division of Human Nutrition, Department of International Health, School of Hygiene and Public Health, Gastroenterology and Nutrition Unit, Department of Pediatrics, School of Medicine, The Johns Hopkins University, Baltimore, MD 21205