Disorders of Fructose Metabolism

Abstract

Fructose is one of the main sweetening agents in the human diet. It is found in the free form in honey, fruit, and many vegetables and associated with glucose in the form of the disaccharide sucrose in even more numerous foods and beverages. Sorbitol, also widely distributed in fruit and vegetables, is converted into fructose in the liver by sorbitol dehydrogenase (Fig. 1). Two inborn errors of fructose metabolism are known. Essential fructosuria is a completely harmless anomaly characterized by the appearance of fructose in the urine after the intake of fructose-containing foods. In hereditary fructose intolerance (HFI), fructose provokes prompt gastrointestinal discomfort and hypoglycemia upon ingestion, although sensitivity varies from patient to patient; it may cause liver and kidney failure when taken persistently and becomes life-threatening when given intravenously. Fructose-1,6-bisphosphatase deficiency, sometimes also considered an inborn error of fructose metabolism, will be discussed in Chap. 8. It is manifested by the appearance of hypoglycemia and lactic acidosis during fasting and may also be life-threatening.