The incidence of hyperbilirubinemia appears to be higher in breast-fed infants than in formula-fed infants. Temporary substitution with formula appears to hasten resolution of the jaundice, and this approach, though controversial, is recommended by the American Academy of Pediatrics. Gourley and colleagues attempted to determine if the specific type of formula (i.e., casein or whey) has an effect on neonatal jaundice.

Sixty full-term neonates were enrolled in the three-week study. They were divided into three groups, with 20 infants each receiving human milk, whey-predominant formula (Enfamil) and a casein-hydrolysate formula (Nutramigen). The formula groups were assigned randomly. Fourteen infants (seven of the breast-fed infants, two Enfamil-fed infants and five Nutramigen-fed infants) were withdrawn from the study before its completion.

All three types of feedings were initiated within 60 minutes of birth and offered on demand every one to three hours. Infants who received alternative feedings or required phototherapy were excluded from the study. The degree of jaundice was assessed daily by a transcutaneous “jaundice index” for the first seven days of life and every two to three days for the subsequent two weeks. The jaundice index has been shown to correlate highly with serum bilirubin concentrations.

Transcutaneous jaundice indexes were significantly higher throughout the study in the breast-fed infants. The jaundice index was significantly higher in the human milk group than in the Enfamil group on days 13 to 19, in the Enfamil group than in the Nutramigen group on days 6 to 16 and in the human milk group than in the Nutramigen group on days 3 to 20.

The authors conclude that jaundice levels are lower in infants fed hydrolyzed casein formula than in infants fed a whey-based formula. They suggest that a possible explanation for this difference is that Nutramigen has been shown to contain an inhibitor of β-glucuronidase, a chemical believed to enhance absorption of intestinal bilirubin, leading to higher serum levels. Further studies are needed to clarify this issue. The findings suggest that infants who develop breast milk jaundice benefit from a casein-based formula such as Nutramigen for a short period while the jaundice is resolving.