Delayed complete functional lactase sufficiency in breast-fed infants.

Colonic fermentation of unabsorbed lactose was evaluated by measuring breath hydrogen (BH2) after a regular feeding in 17 white, normal, exclusively breast-fed infants 4-5 weeks of age. Interval breath samples were collected with a specially modified face mask and analyzed by gas chromatography for H2 and CO2 concentrations. Five infants (29%) produced 20 ppm or more of H2, four of whom underwent repeated testing. Three infants stopped producing over 20 ppm of H2 as they grew older. On a repeat evaluation, one of these three infants had levels over 20 ppm when other foods were introduced into his diet. The other continued to have elevated BH2 when weaned. Stools of infants with elevated BH2 levels had no detectable glucose, and pH was over 5.5. Weight-for-age of infants with elevated BH2 was at or above the 75th percentile. BH2 levels, normalized for the amount of breast milk ingested, fell significantly with age. These results show that complete small bowel absorption of lactose from breast milk does not occur in all white, normal, term, appropriate-for-gestational-age infants in the first months of life. The absence of glucose in the stool and the normal stool pH suggest that the unabsorbed lactose that produced H2 can be degraded in the colon.