Which of the following best explains why fructose was formerly recommended for patients with diabetes mellitus?
ExplanationA special pathway for fructose metabolism (a specific fructokinase plus aldolase B and triokinase) is present in liver, kidney, and small intestine. Foods high in sucrose (glucose-fructose) such as syrups, beverages, or diabetic substitutes yield high concentrations of fructose in the portal vein. Fructose is catabolized more rapidly than glucose by its specific fructokinase, bypassing hexokinase that is regulated by fasting and insulin. While providing a fuel for glycolysis, fructose also increases fatty acid, VLDL, and cholesterol-LDL production that are also side effects of diabetes mellitus due to the necessary shift to fat oxidation when intracellular glucose is less available. Recent data also suggest that fructose in soft drinks and other foods promotes insulin resistance and type II diabetes. For these reasons, the American Diabetic Association (www.diabetes. org) now suggests avoidance of fructose with the exception of naturally occurring fructose in fruits.
