Growth faltering is prevented by breast-feeding in underprivileged infants from Mexico City.

This study was designed to test whether breast-feeding protects infants reared in unfavorable environments from growth-stunting by averting acute infections. The body weight and length, feeding mode and morbidity of 170 healthy infants were assessed at 15-d intervals from birth to 6 mo. Birth weight and length were not different between groups, but at 6 mo, breast-fed infants were heavier and tended to be taller (P = 0.1) than infants fed formula. Relative to NCHS values, infants had lower mean birth weights than a sample of American and European BF infants. At 6 mo, the weight of BF infants caught up to the weight of NCHS standards, while infants fed formula fell to around -1 NCHS-Z-score for weight and length. The cumulative 6-mo weight increments were negatively related to the number of episodes of diarrhea, and positively to duration of lactation (P = 0.03, R(2) = 0.17). The 6-mo length gain was negatively related to infections but not to duration of lactation (P = 0.004, R(2) = 0.19). Never-ill infants attained a better weight (P = 0.04) and length (P = 0.02) than infants who suffered one or more episodes of diarrhea. Weight and length gain of infants suffering at least one episode of diarrhea was positively related to breast-feeding and socioeconomic status. Weight increments of 15-d were positively related to breast-feeding and negatively to the introduction of solids. In conclusion, breast-feeding positively affected the growth performance of the recipient infants by averting infections and possibly by improving nutrient intake during infections.