fruktosa

Fruktosa, also known as fructose, is a monosaccharide, one of the simplest carbohydrates. It is a ketohexose with the molecular formula C6H12O6. Fruktosa occurs naturally in many fruits, honey, and some vegetables and is also produced commercially by hydrolysis of sucrose or enzymatic isomerization of glucose. It is among the sweetest naturally occurring sugars.

In solution, fruktosa exists predominantly in cyclic forms, including beta-D-fructofuranose and related structures. Its relative sweetness is high: fruktosa is generally sweeter than glucose and, under standard conditions, about as sweet as or sweeter than sucrose (estimates commonly range roughly 1.2–1.8 times the sweetness of sucrose, depending on concentration and temperature).

Absorption and metabolism: Fruktosa is absorbed in the small intestine via the GLUT5 transporter and is transported to the liver through the portal circulation. In the liver it is phosphorylated by fructokinase to fructose-1-phosphate and cleaved by aldolase B into dihydroxyacetone phosphate and glyceraldehyde, which enter glycolysis or gluconeogenesis. Unlike glucose, fruktosa uptake does not depend on insulin. Excess intake can promote hepatic lipogenesis and fat accumulation in the liver in some individuals.

Dietary sources and health considerations: Fruktosa is present in fruits and honey and widely used as a sweetener in processed foods, often in the form of high-fructose corn syrup. High intake has been associated with metabolic concerns in observational studies, though causality is debated. Some individuals experience fruktosa malabsorption, and hereditary fructose intolerance is caused by aldolase B deficiency, requiring strict avoidance of fruktosa, sucrose, and sorbitol.