1. Professor of Medicine, Head, Section of Gastroenterology, University of Chicago Pritzker School of Medicine, Chicago, Illinois 60637.
2. Faculty Fellow of the Josiah Macy Jr. Foundation; holds a Future Leader's Award of the Nutrition Foundation. University of Chicago Pritzker School of Medicine, Chicago, Illinois 60637.
3. Division de Biomedica, Institute of Nutrition of Central America and Panama, Guatamala City, Guatamala.