Similar gastric emptying rates for casein- and whey-predominant formulas in preterm infants.

Casein-predominant infant milk formulas have been speculated to predispose to lactobezoar formation in preterm infants due to delayed gastric emptying. There have been, however, no prospective studies to prove this possibility. In a randomized, double-blinded, prospective study, we tested the hypothesis that preterm infants fed casein-predominant milk formula have slower gastric emptying than infants fed whey-predominant formulas. Twenty preterm infants within the first 4 d of life were randomized to receive either the whey-predominant formula Similac Special Care (whey:casein ratio 60:40) or an experimental casein-predominant formula (whey:casein ratio 18:82). Only the protein composition differed between the two formulas. The infants were fed the assigned study formula until they reached approximately 2200 g body weight when a gastric emptying scan was performed, using the designated study formula mixed with 25 microCi of technetium-99 sulfur colloid. Gastric emptying was followed continuously for 2 h. Gastric emptying at 30, 60, 90, and 120 min was similar between the two study groups. The time for 50% gastric emptying was 64.9 +/- 12.3 min for the infants fed the whey-predominant formula and 56.5 +/- 14.8 min for those fed the casein-predominant formula (p = 0.75). We conclude that the rate of gastric emptying in preterm infants fed casein-predominant formulas is similar to that in those fed whey-predominant formulas.