Fecal alpha 1-antitrypsin and infant feeding.

Stool samples from 232 infants aged 7 days to 18 months were analyzed for alpha 1-antitrypsin and for occult blood by two techniques. Among the 450 stool samples, no correlation between positive tests for occult blood and the concentration of alpha 1-antitrypsin was found. The alpha 1-antitrypsin concentration in the stool decreased after the age of 6 months in both breast-fed (P less than 0.05) and formula-fed (P less than 0.001) groups. In the 7- to 30-day-old infants, breast-feeding was associated with both lower fecal alpha 1-antitrypsin (P less than 0.001) and less frequent positive tests for occult blood (P less than 0.02) than found in the formula-fed infants. Between 6 and 12 months of age, alpha 1-antitrypsin was lower in cow milk-fed infants than in those receiving either breast-feeding supplemented with formula (P less than 0.01) or soy formula (P less than 0.05). Age and feeding differences in the concentration of alpha 1-antitrypsin in the stool may reflect subtle changes in gastrointestinal tract function in infancy.