Hexose absorption in the small intestine has long been understood to be mediated by at least three proteins. Uptake across the apical membrane (BBM) involves a sodium-coupled active transporter (SGLT1) and two facilitated transporters, GLUT5 and GLUT2. Exit across the basolateral membrane occurs via GLUT2. All three are expressed predominately in the duodenum and jejunum and at a much lower level in the ileum and not at all in the colon. A reserve capacity for the absorption of hexoses is ensured by changes in the expression of these proteins in parallel with the dietary content of carbohydrate. This adaptive response takes several days to be fully realized and appears to be programmed as enterocytes leave the crypts and migrate onto the villi. The sequencing of the human genome has led to the identification of several additional members of the GLUT protein family (SLC2A genes), which are now grouped into three sub-classes (1). Recently, this laboratory cloned GLUT7 (SLC2A7), a class II GLUT most closely related to GLUT5 (2). It is a high affinity glucose and fructose transporter isoform which is expressed predominantly in the BBM of the ileum and colon. Unlike the class I GLUTs (1-4), which have a Km in the mM range, the class II proteins are high affinity with Km in the range of 100-300 μM. The majority appear to transport fructose as well as glucose, but not galactose or 2-deoxyglucose, which would explain why expression cloning using the latter substrate failed to identify these proteins. We have examined the effect of altered dietary carbohydrate content on the expression of intestinal GLUT7 to determine if it is changed in a similar manner to the other intestinal hexose transporters, which could indicate that this protein also plays a role in the absorption of nutritional hexoses. In addition, we investigated if GLUT9 (3), another class II member known to be expressed in the kidney, is found in the intestine. Rats were maintained for 7 days on one of three diets, normal rat chow, a low carbohydrate diet, LC (23% glucose & 7.7% corn starch) or a high carbohydrate diet, HC (44 % glucose & 14.75% corn starch). The LC and HC diets were formulated to be isocaloric by changing the carbohydrate and fat content reciprocally. After 1 week on the diets, the animals were terminally anesthetized and the jejunum, ileum and colon excised for mRNA preparation, immunohistochemistry and Western blotting of isolated membranes. We found that ileal brush-border membranes from HC-fed rats had significantly greater expression of GLUT7 than those on the LC diet. GLUT9 was found to be expressed in the ileal and colonic apical membranes, but the level of expression of this protein in the colon was decreased by the HC diet. These data indicate that GLUT7 may play a role in hexose absorption during the later stages of a meal. This is also the first demonstration that GLUT9 is expressed in the intestine, primarily in the apical membrane of the colon, a tissue which is not believed to be normally involved in hexose absorption. However, its expression increased when the fat content of the diet was raised suggesting that perhaps, like a related isoform HMIT (SLC2A13), its primary substrates are not hexoses (4).