Facilitating effect of amino acids on fructose and sorbitol absorption in children

The facilitating effect of glucose on free fructose absorption has been suggested to be due to a sucrase-related transport mechanism. In contrast, the conditions influencing the absorption of sorbitol have hardly been investigated. As amino acids promote transcellular water flow, we investigated their effects on the absorption of fructose and sorbitol. We studied 15 healthy children using breath hydrogen tests following the ingestion of fructose and sorbitol, alone and in combination with glucose or amino acids. Similarly, the effect of acarbose pretreatment on sucrose and fructose-glucose absorption was investigated. The inhibition of sucrase isomaltase by acarbose impedes the absorption of sucrose but not of the fructose-glucose mixture. Fructose absorption is enhanced by glucose and by the amino acids L-alanine, L-glutamine, L-phenylalanine, and L-proline. Similarly, the absorption of sorbitol is facilitated by glucose and L-alanine. These results are not in concordance with a sucrase-related fructose-transport system and suggest another mechanism for glucose-induced enhancement of fructose (and sorbitol) absorption. We hypothesize that the absorption of fructose and sorbitol may be stimulated by the increased water flux induced by active absorption of glucose as well as amino acids.