Effects of oral D-tagatose, a stereoisomer of D-fructose, on liver metabolism in man as examined by 31P-magnetic resonance spectroscopy.

D-tagatose, which is a stereoisomer of D-fructose, is phosphorylated to D-tagatose-1-phosphate by fructokinase in the liver. Because of a slow degradation rate of D-tagatose-1-phosphate, this substance may accumulate, and ingested D-tagatose may therefore cause a longer lasting reduction in inorganic phosphate (Pi) and adenosine triphosphate (ATP) levels in the liver compared with D-fructose. Similar to what is seen in patients with hereditary fructose intolerance, this may increase purine nucleotide degradation and thereby increase uric acid production. The effect of 30 g D-tagatose or D-fructose administered orally on ketohexose-1-phosphates, ATP, and Pi levels in the liver was studied by 31P-magnetic resonance spectroscopy (PMRS) in 5 young male volunteers. Blood and urine were collected to detect a possible increased uric acid production. A peak at 5.2 ppm assigned as D-tagatose-1-phosphate equivalent to about 1 mmol/L was found in the spectrum within 30 minutes after D-tagatose was administered in all subjects. Concomitantly, ATP was reduced by about 12% (P < .05). Both effects had vanished after 150 minutes. Serum uric acid concentration was increased by 17% 50 minutes after D-tagatose (P < .05) and did not reach baseline level when the experiment was terminated 230 minutes after the load. Although renal fractional extraction of uric acid decreased by approximately 12%, this could not explain the acute hyperuricemic effect of D-tagatose. No changes in 31PMRS spectra or serum uric acid concentration were found after D-fructose. These results suggest that a moderate intake of D-tagatose may affect liver metabolism by phosphate trapping despite the fact that the sugar may only be incompletely absorbed in the gut.