D-TAGATOSE, A STEREOISOMER OF D-FRUCTOSE, INCREASES HYDROGEN-PRODUCTION IN HUMANS WITHOUT AFFECTING 24-HOUR ENERGY-EXPENDITURE OR RESPIRATORY EXCHANGE RATIO

In growth studies on rats, the ketohexose D-tagatose has been shown to contribute no net metabolizable energy, and a pronounced thermic effe ct of the sugar has been suggested to account for the absence of energ y. In a double-blind and balanced cross-over design, we measured 24-h energy expenditure in eight normal weight humans in a respiration cham ber during the consumption of 30 g D-tagatose or 30 g sucrose/d. Metab olic measurements were performed before and after a 2-wk adaptation pe riod with a 30-g daily intake of the test sugar. Total 24-h energy exp enditure and hour-by-hour profile were unaffected by the test sugar. T he nonprotein respiratory exchange ratio (RERnp) was similar during co nsumption of D-tagatose and sucrose. However, the effect on RERnp due to CO, produced by fermentation of D-tagatose could not be quantified in this study. A significant increase in 24-h H-2 production (35%) dur ing D-tagatose administration suggests a substantial malabsorption of the sugar. We found no effects of the 2-wk adaptation period on the me asured gas exchange variables. Significantly lower fasting plasma insu lin and triglyceride concentrations were observed during D-tagatose ad ministration compared with the sucrose period. No effects of D-tagatos e on body weight and composition were seen, but the perception of full ness 2.5 h after the sugar load was greater with D-tagatose. In conclu sion, this study does not suggest a pronounced thermic effect of D-tag atose, and other mechanisms seem to be required to explain its lack of net energy.