Length and weight were measured at baseline and at 6 and 12 mo after enrollment. Weight was measured to the nearest 10 g using an electronic scale (Tanita, Model 1583, Tokyo, Japan). Length was measured to the nearest millimeter using a locally made measuring board in children <24 months of age and standing height, using a stadimeter with precision of 1 mm (Dyna-Top, model E-1,Mexico City, Mexico) in children 24 months or older. The measurements were obtained using standard techniques (19, 20). The birth date was reported by the mother and corroborated in a large proportion of children using birth certificates. Length and weight data were transformed to z-scores by using the WHO/NCHS/CDC reference data (21).