The remarkable activation of the fructose transporter GLUT5 in the small intestine of obese individuals [118] mimics the upregulation of GLUT5 in the jejunum of rodents fed high fructose diets [95,96,97,109], and points to the stimulatory role of increased fructose consumption on the expression of GLUT5 in humans with metabolic syndrome/obesity. The gene discussed is SLC2A5; the disease is obesity due to melanocortin 4 receptor deficiency.