Comparison of the Colonic Metabolism in Patients With Lactose Intolerance and Healthy Controls

Most people are born with the ability to digest lactose, a dissacharide consisting of β-D-glucose and β-D-galactose, because of the presence of lactase at the brush border of the small intestine. In about 75% of the world population the activity of this enzyme decreases after weaning (primary hypolactasia or lactase-nonpersistence), resulting in incomplete digestion of lactose and lactose malabsorption in adulthood (1). Secondary forms of lactose malabsorption may be due to inflammation or functional loss of the intestinal mucosa such as celiac disease, infectious enteritis or Crohn's disease. Very rarely, lactase deficiency is congenital due to an autosomal recessive genetic disorder, preventing lactase expression from birth (2). Whereas some people with lactose malabsorption are asymptomatic, most lactose-nonpersisters experience symptoms like abdominal pain, bloating, excess flatulence or diarrhea. Lactose intolerance refers to the syndrome of having one or more symptoms after consumption of lactose-containing food (3). At present, the origin of the symptoms of lactose-intolerance is not well understood. Several studies have indicated a poor correlation between lactose maldigestion and symptoms of lactose intolerance (4). In a study by Vonk et al. (2003), lactose intolerant subjects with severe symptoms (diarrhea) and intolerant subjects with only mild symptoms (without diarrhea) did not differ in degree of lactose digestion in the small intestine indicating a similar lactase activity and leading them to the hypothesis of a "colon resistence factor" (5). It was suggested that the colonic processing of maldigested lactose may play a role in the symptoms experienced by lactose intolerant patients. When lactose is malabsorbed and enters the colon, it is rapidly fermented by the resident microbiota into a variety of metabolites including lactate, formate, succinate and short chain fatty acids (SCFA, acetate, propionate, butyrate) as well as gases (H2, CO2 and CH4).