Lactose assimilation by full-term infants: Relation of [13C] and H2 breath tests with fecal [13C] excretion

Abstract

Colonic salvage of malabsorbed carbohydrate is probably a quantitatively important mechanism of lactose assimilation in the premature infant. The relative roles of the small and large intestines in carbohydrate absorption have not been assessed in the full-term infant. The [13Cl-l-lactose (13C-1-L) breath test was first validated against [14C]-l-lactose (14C-1-L) in seven adult volunteers. Individual coefficients of correlation of the regression of % dose [13C] (% d [13C]) on % dose [14C] (% d [14C]) for the seven adults varied from 0.950-0.997; the ratio of the cumulative % dose [13C] (cum % [13C]) to the cumulative % dose [14C] (cum % [14C]) ranged from 0.89-1.15. Nineteen full-term infants (40.1 ± 0.9 wk gestation) were subsequently studied. On day 1 baseline breath and stool collections were carried out with unlabeled substrate (lactose-containing formula). In the initial ten infants [13C]-1-L was added to the 7 a.m. or 8 a.m. formula feeding on day 2 and an 8-h breath test was done. A 24-h stool collection was also carried out. In nine subsequent infants a breath test and stool collection with [l3C]-l-glucose ([13C]-1-G) were carried out on day 2 and the studies with [13C)-1-L were moved to day 3. H2 and % d [13C]/h and cum % [13C] in breath and [I3C] recovered in stool were determined. All infants had detectable H2 in breath on the days of study. Peak H2 excretion was <20 ppm in eleven infants. >20 ppm in eight. There was no relationship of H2 excretion to gestational age, birth weight, postnatal age or lactose intake. In all 19 infants the % d [13C] in breath per h and the cum % [13C] after [13C]-1-L were virtually identical to data in adults studies after consumption of naturally [13C]-labeled maize glucose. In the infants studied with both substrates, there were no significant differences between [13C]-1-L and [13C]-1-G in % d [13C] at each time point. Cum % [13C] recovered from [13C]-1-G become progressively greater than that from [13C]-1-L, significantly so at 6, 7, and 8 h (8 hour % d [13C]: lactose, 32.6 ± 3.5% and glucose, 35.5 ± 3.1%; paired t = 2.528, P < 0.05). Excess [13C) (1.9% of dose) was detected in the stool of only one infant in the 24 h after [13C]-1-G ingestion. Fecal [13C] after [13C]-1-L was 1.6% of the dose in nine infants (range 1.6-6.8%). Breath and stool data from these studies imply that lactose absorption in the small intestine by the formula-fed full-term infant is nearly complete. Colonic salvage of carbohydrate occurs but is variable and appears to be quantitatively less important than is suspected in premature infants. © 1983 International Pediatric Research Foundation, Inc.