A Randomized, Double-blind, Patient-control Trial to Study Weight Gain in Premature Newborns Receiving Lactase-fortified Milk

Lactose, a disaccharide that includes the monosaccharides glucose and galactose, is the main carbohydrate found exclusively in mammalian milk. The absorption of lactose requires lactase activity to break the bond that binds the 2 monosaccharides. Lactase is found in the intestinal mucosa and is located at the ends of the villi, while it is a factor of maximum clinical importance in milk tolerance and in the occurrence of diarrheal disease.

Milk intolerance can be attributed to either lactose or protein content. Lactose intolerance may occur in infants and young children with acute diarrhoea, although its clinical significance is limited. Lactose intolerance symptoms are relatively common among older children and adolescents. However, associated intestinal damage is rarely observed. Lactose tolerance is a separate entity from cow's milk protein allergy, which is of immune etiology and can cause varying degrees of intestinal mucosal injury. Cow's milk protein intolerance is reported in 2% to 5% of infants within the first 1 to 3 months of life, usually subsides by the age of 1 year and is not the subject of this statement.

In more specific cases, the hydrogen breath test is the least invasive and most helpful test for diagnosing lactose malabsorption. The test is performed by administering a standardized amount of lactose (2 g/kg, up to a maximum of 25 g, equivalent to the amount of lactose in 2 glasses of milk) after fasting overnight and then measuring the amount of hydrogen in the exhaled air for a period of 2 to 3 hours. An increase (20 ppm) in hydrogen after about 60 minutes is indicative of lactose malabsorption. Factors that may produce false negative or false positive results include conditions affecting the intestinal flora (e.g., recent use of antimicrobial agents), lack of hydrogen-producing bacteria (10%-15% of the population), ingestion of a high-fiber diet before testing, bacterial overgrowth of the small intestine, or intestinal motility disorders.

In newborns and infants with diarrhea in whom lactose (or other carbohydrate) intolerance is suspected, the stool can be checked for carbohydrate malabsorption by testing the pH of the stool, which is reduced by carbohydrate malabsorption as a result of the formation of volatile fatty acids. It is noted that the pH of the stool is lower in infants compared to older children and adolescents due to the normal overload of lactose in their diet; which in turn helps to promote the growth of Lactobacillus species in the large intestine. Reducing substances can also be detected in the stool, such as reducing sugars that include lactose, glucose, fructose and galactose, but not sucrose. Because some patients may only absorb enough carbohydrates, such as lactose, to lower the pH of the stool but not increase the excretion of carbohydrates in the stool, the pH test is a more sensitive test for carbohydrate malabsorption.

Developmental lactase deficiency is defined as the relative lactase deficiency observed in premature newborns less than 34 weeks of gestation. In the immature gastrointestinal tract, lactase and other disaccharidesas are deficient until at least 34 weeks of gestation. One study in premature babies reported a benefit from the use of lactase-supplemented foods or lactose-reduced preparations. While the use of lactose-containing preparations and human milk does not appear to have short- or long-term harmful effects on newborns and infants. Up to 20% of dietary lactose can reach the colon in newborns and young infants. The metabolism of lactose by colon microbes lowers the pH of the stool, which has a beneficial effect, favoring certain organisms (e.g. Bifidobacterium and Lactobacillus species) instead of potential pathogens (Proteus, Escherichia coli and Klebsiella species) in young infants.