401 tion in a physiologic range of lactose in- takes). A preliminary report of older infants addressed whether an increased intake of a fermentable sugar affected physical ac- tivity (presumably through effects on colon function, abdominal discomfort, etc). 8 Therefore we also determined whether doubling the lactose intake had any effect on energy expenditure as de- termined by measurement of carbon dioxide production. METHODS Subject Population This study was approved by the local human studies committee. Healthy pre- term infants born before 32 weeks’ ges- tational age, who did not receive intra- venous antibiotics or respirator therapy and who had no significant gastrointesti- nal dysfunction, were studied. All infants were being fed preterm in- fant formula (Similac Special Care For- mula; Ross Products Division of Abbott Laboratories, Columbus, Ohio) before the study; the carbohydrate in this formu- la is approximately 50% lactose and 50% glucose polymer. The infants then partici- pated in a “double masked” crossover study in which digestion and carbohy- drate fermentation were compared while Lactose is an important constituent of human or cow’s milk and infant formu- las. Lactose utilization is often evaluated by assessing breath H 2 concentration to measure fermentation by H 2 -producing E E ffects of lactose intake on lactose digestion and colonic fermentation in preterm infants C. Lawrence Kien, MD, PhD, Richard E. McClead, MD, and Leandro Cordero, Jr, MD bacteria. Doubling the lactose intake of preterm infants caused a doubling of breath H 2 concentration, confirming pre- vious suggestions that lactose digestion develops late in gestation. 1 H owever, hy- drolysis (digestion) of lactose to glucose and galactose, measured by using a sta- ble isotope technique, 2 is variable (30% to 100%) in preterm infants of 31 to 37 weeks’ postconceptional age. 2,3 Preterm infants tolerate and thrive on human milk and formulas containing lac- tose as the sole carbohydrate and excrete only small amounts of lactose-derived energy or carbon in their feces. 4-7 The objective of this study was to determine whether doubling the lactose intake would decrease the fraction of lactose di- gestion and increase breath H 2 excretion (suggesting a finite limit to lactose diges- From The Children’s Hospital Research Foundation, De- partment of Pediatrics, T he Ohio State University, and T he Ohio State University Hospitals, Columbus, Ohio. Supported in part by National Institutes of Health grants nos. HD 19773 and M01 RR00034 (General Clinical Research Center) and by Ross Products Division of Abbott Laboratories, Inc (provision of formula). Submitted for publication J uly 29, 1997; revisions received J an 6, 1998, and May 12, 1998; accepted J une 23, 1998. Reprint requests: C. Lawrence Kien, MD, PhD, Room W209, Children’s Hospital, 700 Children’s Dr, Columbus, OH 43205. Copyright © 1998 by Mosby, Inc. 0022-3476/98/$5.00 + 0 9/21/92601 f hydrL Percentage of lactose digested to glucose CG 13 C-labeled glucose corrected for recycled label dG Infusion rate, glucose tracer dL Infusion rate, lactose tracer IE Isotopic enrichment LAC Ross Special Care Formula containing lactose as sole carbohydrate RLD Relative lactose digestion SC Ross Special Care Formula VCO 2 N et rate of respiratory CO 2 excretion (production) The purpose of this study was to determine whether doubling the lactose con- centration in formula for preterm infants lowers the fraction of lactose digested and/or increases the fraction of lactose fermented. Six preterm infants, 31 to 36 weeks’ postconceptional age, were fed a standard preterm formula (carbohy- drate is 50% lactose and 50% glucose polymer)(SC) and/or the same volume of formula modified to contain lactose as the sole carbohydrate (LAC). Relative lactose digestion during the LAC formula feeding compared with SC formula feeding was measured by using a stable isotope approach for quantifying the fractional contribution of formula lactose to plasma glucose enrichment. Rela- tive lactose digestion was 0.98 ± 0.17 (range, 0.70 to 1.19). Fractional fermenta- tion of lactose was estimated from breath H 2 excretion (0.52 ± 0.34 during LAC feeding and 0.23 ± 0.22 during SC feeding, P = .11). The rate of breath H 2 ex- cretion was much higher with LAC (1.34 ± 0.98 mL/h) than with SC (0.27 ± 0.29, P = .029). In conclusion, doubling the lactose concentration had only mod- est effects on fractional lactose digestion. Increased breath H 2 excretion with LAC may relate to fermentation of nonlactose sugar or to ill-defined changes in colonic physiology or motility, which could enhance colonic fermentation of malabsorbed sugar by H 2 -producing bacteria. (J Pediatr 1998;133:401-5)