frutose

Fructose, commonly called fruit sugar, is a simple sugar (monosaccharide) and a ketohexose. It is an isomer of glucose and one of the sweetest naturally occurring carbohydrates. In nature it occurs freely in fruits, honey, and certain vegetables and is a component of sucrose, the disaccharide formed from glucose and fructose. Fructose is also produced commercially as a sweetener for foods and beverages, most notably in high-fructose corn syrup (HFCS), which is used to adjust sweetness and shelf life.

In solution fructose exists in multiple ring forms, including furanose and pyranose forms, and interconverts with its open-chain form.

Metabolism: Fructose is absorbed in the small intestine via the transporter GLUT5 and delivered to the liver via the portal vein. In hepatocytes it is phosphorylated by fructokinase to fructose-1-phosphate and subsequently split by aldolase B into dihydroxyacetone phosphate (DHAP) and glyceraldehyde, which is then converted to glyceraldehyde-3-phosphate. These triose phosphates enter glycolysis or gluconeogenesis. Because fructose metabolism bypasses the major regulatory step of glycolysis (phosphofructokinase-1), excessive intake can promote de novo lipogenesis and fat accumulation in the liver, though the extent depends on overall energy balance and substrate availability.

Dietary considerations: Fructose from fruits and vegetables is accompanied by fiber, vitamins, and polyphenols and is generally considered part of a balanced diet. Added fructose, especially in sweetened beverages and processed foods, can contribute to excess energy intake and metabolic effects in some individuals. Public health guidance emphasizes limiting added sugars.