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Plasma Rare Sugar Levels and the Effect on Plasma Glucose Levels in GLUT5‐induced Rats Gavaged with Rare Sugar D‐Sorbose, D‐Tagatose, or D‐Allose

D‐Sorbose, D‐tagatose, and D‐allose are rare sugars that have been reported to have various beneficial health effects 1 , 2) . They are contained in Rare Sugar Syrup as functional ingredients 3) . It is essential to clarify which transporters are involved in their intestinal absorption to elucidate their physiological effects and also to apply them to “Foods with Function Claims”. We have already reported that D‐allulose, an epimer of fructose, was a substrate of glucose transporter type 5 (GLUT5) in the small intestine 4 , 5) . GLUT5 is a transporter that mediates intestinal fructose absorption. In the present study, we examined whether D‐sorbose, D‐tagatose, and D‐allose are absorbed via GLUT5 in the small intestine and also compared the effects on plasma glucose levels after gavage administration of these rare sugars. We divided rats into 2 groups. One group was fed high‐fructose diet, and the other group was fed high‐glucose diet for a week. Fructose‐fed rats induced their intestinal GLUT5 expression. Then, we gavaged the rats with 2g/kg BW of D‐sorbose, D‐tagatose, or D‐allose, and collected blood at 0, 30, 60, 90, 120, 180 min from the tail vein into a heparinized tube. Plasma levels of rare sugars and glucose were analyzed by HPLC. When D‐sorbose was gavaged to the rats, the fructose‐fed rats exhibited significantly higher D‐sorbose levels than the glucose‐fed rats at 30, 60, 90, 120 min. A similar result was obtained with D‐tagatose administration experiment. By contrast, D‐allose levels did not differ between the fructose‐fed and glucose‐fed rats when D‐allose was gavaged to the rats. These results suggest that D‐sorbose, D‐tagatose but not D‐allose are absorbed via GLUT5 in the small intestine. The fructose‐fed rats exhibited significantly higher plasma glucose levels only when D‐tagatose was gavaged. As D‐tagatose was reported to be a substrate of gluconeogenesis 6) . The results indicate that more D‐tagatose was absorbed in the fructose‐fed, GLUT5‐induced rats, resulting in the higher conversion into glucose than in the glucose‐fed rats.