Which transporter is primarily responsible for fructose absorption from the intestinal lumen?

• A. Fructose absorption from the intestinal lumen is primarily mediated by GLUT5, which mediates passive diffusion.
• B. Fructose uses SGLT1 in the apical membrane for active transport.
• C. Fructose is absorbed by GLUT2 on the apical membrane via active transport.
• D. Fructose is absorbed across the basolateral membrane by SGLT1.

Answer: (A)

Fructose is taken up from the intestinal lumen into the enterocytes mainly by a specific facilitated transporter called GLUT5 on the apical (brush-border) side. This process is a passive diffusion—fructose moves down its concentration gradient without energy use. After entering the cell, fructose exits to the bloodstream primarily through GLUT2 on the basolateral membrane. SGLT1 is the sodium-glucose cotransporter and handles glucose (not fructose), so it doesn’t mediate fructose uptake. In some situations, GLUT2 can be recruited to the apical membrane to help with high luminal fructose, but the primary step from lumen to cell is GLUT5-mediated facilitated diffusion.