Disaccharidase Deficiency
Martin H. Ulshen MD1
1 Associate Professor of Pediatrics, Chief, Division of Pediatric Gastroenterology, University of North Carolina School of Medicine, Chapel Hill, NC 27514
Disaccharidases are enzymes of the small intestine, and they are essential for normal carbohydrate digestion. Carbohydrates are an important dietary component, providing about half of the calories in a typical Western diet. The smallest carbohydrate units, the monosaccharides, are the building blocks for more complex sugars and starches. The monosaccharides of dietary importance include glucose, galactose, and fructose. Carbohydrates are present in an average diet, primarily in the form of dissacharides (two monosaccharides linked together) and starches (glucose polymers). The disaccharide lactose is the major carbohydrate in milk and accounts for about 40% of the caloric content of human milk as well as commercial cow milk formula. Lactose is composed of the monosaccharides glucose and galactose; sucrose is composed of glucose and fructose. During the first year of life, juices and solids are introduced into the diet in increasing amounts and, therefore, sucrose and starches provide an increasing proportion of the dietary calories. By the adult years, about 50% of dietary carbohydrate is ingested in the form of starch, and lactose is often a minor component of the diet.
Among the dietary carbohydrates, only the monosaccharides can be transported intact across the luminal surface of the small intestine. The moroe complex carbohydrates must undergo digestion prior to assimilation.
