Rates and mechanisms of glucose, galactose, and xylose absorption in man in vivo.

Jejunal absorption-rates of glucose, galactose, and xylose were determined consecutively, using a double-lumen tube perfusion technique, in 6 Arab subjects in vivo; perfusion solutions contained 200 mmol/l of each monosaccharide. Mean xylose absorption rate was significantly lower than that for glucose (P less than 0.001) and galactose (P less than 0.001). In order to investigate evidence that glucose and xylose share the same jejunal transfer mechanism, their absorption-rates when given alone and together, at high concentrations, were determined in 6 other Arabs; perfusion solutions contained (1) 200 mmol/l glucose, (2) 100 mmol/l xylose, and (3) 200 mmol/l glucose + 100 mmol/l xylose. Rates of glucose and xylose absorption were not significantly influenced by the other monosaccharide. This study does not therefore confirm existence of a common transfer mechanism. A significant correlation between absorption rate of glucose and weight of xylose excreted after a 25 g oral load (P less than 0.05) was demonstrated.