GLUT5 is a fructose transporter expressed on the apical border of enterocytes in the small intestine. GLUT5 allows for fructose to be transported from the intestinal lumen into the enterocyte by facilitated diffusion due to fructose's high concentration in the intestinal lumen. GLUT5 is also expressed in skeletal muscle, testis, kidney, fat tissue, and brain.In addition, GLUT5 is probably responsible for the uptake of fructose by spermatozoa. The pattern of GLUT5 immunoreactivity in maturing spermatids suggested that the expression of GLUT5 may serve as a marker for terminal maturation of male germ cells. An increasing fraction of calories consumed in Western diets is derived from fructose. Increases in fructose consumption have been implicated in a rising incidence of hypertriglyceridemia and hyperinsulinemia.