Since the Committee on Nutrition issued its first statement on "The Practical Significance of Lactose Intolerance in Children" in 1978,1 there have been a few interesting clinical advances in our knowledge of the digestion of lactose. We suggest that the original statement be reviewed to provide a framework for the information presented here.
Lactose is a disaccharide that is present in almost all mammalian milks. It is digested in the small bowel by the lactase located on the brush border of the enterocyte. On digestion, lactose is broken down into two components, glucose and galactose. If lactose is not digested or is digested minimally, the intact sugar moves into the large bowel where it is fermented by enteric bacteria. This fermentation produces acids, carbon dioxide, methane, and hydrogen, and usually results in borborygmi and abdominal discomfort. Lack of digestion of lactose results in an increased number of solute particles in the large bowel with a concomitant increase in osmotic pressure. It has been suggested that the diarrhea associated with lactose intolerance occurs when the capacity of the bacteria to metabolize carbohydrate in the colon has been exceeded.2 Consequently, there is a flow of fluid into the lumen of the bowel with a resultant watery, fermentative diarrhea. These clinical signs and symptoms represent lactose intolerance, a condition that results from malabsorption and lack of digestion of lactose.
There are two useful clinical tests for lactose malabsorption. One test measures the increase in the concentration of glucose in blood following administration of a load of lactose (1 g/kg up to 50 g/kg, equivalent to a liter of milk).
- Copyright © 1990 by the American Academy of Pediatrics