Category: sugar
Aliases: Fruit sugar, Levulose, D-Fructose, D-Fructofuranose, β-D-Fructose
Ketohexose monosaccharide (C6H12O6, isomeric with glucose); the sweetest common dietary sugar. Absorbed across the apical enterocyte by the facilitative transporter GLUT5 (SLC2A5) and exported basolaterally via GLUT2 — both insulin-independent. Apical GLUT5 capacity is the rate-limiting step, so excess fructose load (especially without co-ingested glucose) overwhelms it and drives fructose malabsorption with osmotic diarrhea and colonic fermentation. Cleared predominantly by first-pass hepatic metabolism: ketohexokinase (KHK/fructokinase) phosphorylates it to fructose-1-phosphate, which aldolase B splits to triose phosphates, bypassing the PFK-1 rate-limiting step of glycolysis. This unregulated entry favors de novo lipogenesis, uric-acid generation (ATP/phosphate depletion → AMP catabolism), and minimal direct insulin secretion. As the sucrose hydrolysis product (with glucose) and a polyol-pathway/sorbitol endpoint.
No E-number (a food/sweetener, not an additive); GRAS in the US, JECFA ADI "not specified." About 1.2-1.8x as sweet as sucrose (sweetness falls with warming as the furanose form predominates). Key flags: hereditary fructose intolerance (aldolase B deficiency) is dangerous; high intakes promote fructose malabsorption, hepatic de novo lipogenesis, and hyperuricemia.