Fructose

Fructose is a simple sugar found in fruit and present as one component of sucrose. Its formula is C₆H₁₂O₆, the same as that of glucose, but its open-chain form contains a ketone group rather than an aldehyde group. It is therefore classified as a ketohexose.

Absorption and metabolism

Ingested fructose is absorbed through the intestine, principally by the transporter GLUT5. The amount that can be absorbed varies, and absorption is not unlimited. Fructose reaching the liver is rapidly processed through pathways that differ in their first steps from those handling glucose.

The enzyme ketohexokinase, also called fructokinase, converts fructose to fructose-1-phosphate. Subsequent reactions produce compounds that can enter broader carbohydrate metabolism. Their eventual use depends on nutritional and hormonal conditions: the carbon can contribute to several pathways rather than having one inevitable destination. The intestine can also metabolise fructose; the liver is not the only tissue involved.

Food and research context

Fructose occurs both in foods and in manufactured sweeteners. In sucrose it is chemically joined to glucose; high-fructose corn syrup contains the two sugars in unbound form. Research on excessive sugar intake must distinguish the amount consumed, the food or drink supplying it and the overall diet. A mechanistic finding about fructose metabolism does not establish that all fructose-containing foods have identical effects, or that results from a high-dose animal experiment describe an ordinary human diet.

Attribution

Prepared with reference to the structure and linked topics of the English Wikipedia article, revision 1372954917. Rewritten and checked against the sources cited above; changes have been made. Wikipedia contributors’ material is available under CC BY-SA 4.0.