fructose

Fructose is a simple sugar, a monosaccharide and a ketohexose with the formula C6H12O6. It is an isomer of glucose, sharing the same chemical formula but differing in structure and reactivity. Fructose naturally occurs in fruits, honey, and many vegetables, and is a major component of sucrose, which is a disaccharide of glucose and fructose. It is also widely used in processed foods as a sweetness ingredient in high-fructose corn syrup and other sweeteners.

In humans, fructose is absorbed from the intestine and transported to the liver via the portal vein. In the liver, fructose is phosphorylated by fructokinase to fructose-1-phosphate and then split by aldolase B into dihydroxyacetone phosphate and glyceraldehyde, which can enter glycolysis or gluconeogenesis. This pathway bypasses the main regulatory step of glycolysis governed by phosphofructokinase-1, leading to relatively rapid hepatic metabolism. Unlike glucose, fructose does not acutely raise insulin levels.

Dietary intake of fructose has been the subject of health discussions. Moderate consumption as part of a balanced diet is generally considered safe for healthy individuals. Excessive intake, particularly from added sugars, has been associated with increased risk of obesity, insulin resistance, fatty liver disease, and elevated uric acid in some studies. Some individuals have hereditary fructose intolerance due to aldolase B deficiency and must avoid or limit fructose and sucrose.

Fruits provide fructose alongside fiber, vitamins, and minerals, which can modulate intake and contribute to a nutrient-rich diet. Regulatory guidelines typically emphasize limiting added sugars rather than restricting naturally occurring fructose in whole foods.