The simultaneous ingestion of glucose can improve fructose absorption and prevent symptoms. In 1984, it was described that children showed increased breath hydrogen excretion after administration of 2 g/kg (max. 50 g) fructose but not after ingestion of fructose together with equimolar amounts of glucose or galactose. Only the three children with the highest breath hydrogen peaks demonstrated abdominal symptoms [
14]. This effect was confirmed by Rumessen et al. in 10 healthy adults. An elevated breath hydrogen excretion after ingestion of 50 g fructose was observed in 7 out of 10 people. In contrast, breath hydrogen peaks were normal after simultaneous ingestion of equimolar amounts glucose [
19]. Patients with fructose malabsorption can additionally consume glucose if they want to eat fructose-rich food to avoid symptoms. The reason for this absorption enhancing effect is under discussion. Fructose could be passively absorbed due to glucose-stimulated water absorption. The observation that this beneficial effect was not only mediated by sugars but also by amino acids such as alanine supports this hypothesis [
20]. However, fructose transport was not enhanced after ingestion of fructose and urate in equal amounts [
14]. Another explanation is the presence of a glucose dependent fructose co-transport system [
19]. An involvement of the fructose and glucose transporter GLUT2 has been proposed because trafficking of GLUT2 to the apical membrane after glucose load was observed in rats [
8]. In contrast, no evidence for GLUT2 presence in the apical brush-border membrane in response to glucose was shown by Röder et al. indicating the involvement of other transporters [
9]. In a cohort of six healthy subjects, it was observed that glucose and galactose can prolongate gastric emptying [
21]. Possibly, the delayed arrival of fructose in the small intestine due to delayed gastric emptying could explain the increased fructose absorption by simultaneous glucose administration. Moreover, an enhancing effect of glucose and lipids on sorbitol absorption was demonstrated which might be explained by similar mechanisms [
22].