Fruktose

Fruktose, or fructose, is a monosaccharide and one of the hexose sugars. It has the chemical formula C6H12O6 and is the sweetest naturally occurring carbohydrate. Fruktose occurs naturally in fruits, honey, and some vegetables, and is a component of sucrose (table sugar) and of many syrups used as sweeteners.

Humans absorb fructose in the small intestine via the GLUT5 transporter and transport it to the liver, where it is phosphorylated by fructokinase to fructose-1-phosphate. It is cleaved by aldolase B to dihydroxyacetone phosphate and glyceraldehyde, which can enter glycolysis or lipogenesis. Fruktose metabolism is not tightly regulated by insulin and can have rapid, dose-dependent effects on hepatic fat synthesis and uric acid production.

Dietary sources include fruit, honey, and sweeteners such as sucrose and high-fructose corn syrup. In many foods fructose is present as part of sucrose, a disaccharide of glucose and fructose, or in free form in syrups.

Health considerations: high intake of added fructose, especially from sweetened beverages and highly processed foods, has been associated with increased triglycerides, insulin resistance, and non-alcoholic fatty liver disease in some studies, though results vary and total energy intake is important. The debate continues about whether fructose itself is uniquely harmful or whether excess calories drive observed effects.

Medical conditions: hereditary fructose intolerance due to aldolase B deficiency leads to dangerous accumulation of fructose metabolites after fruit consumption; essential fructosuria results from fructokinase deficiency and is usually benign; fructose malabsorption can cause gastrointestinal symptoms when absorption capacity is exceeded.