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 effect of the sugar has been suggested to account for the absence of energy. In a double-blind and balanced cross-over design, we measured 24-h energy expenditure in eight normal weight humans in a respiration chamber during the consumption of 30 g D-tagatose or 30 g sucrose/d. Metabolic measurements were performed before and after a 2-wk adaptation period with a 30-g daily intake of the test sugar. Total 24-h energy expenditure and hour-by-hour profile were unaffected by the test sugar. The nonprotein respiratory exchange ratio (RERnp) was similar during consumption of D-tagatose and sucrose. However, the effect on RERnp due to CO2 produced by fermentation of D-tagatose could not be quantified in this study. A significant increase in 24-h H2 production (35%) during D-tagatose administration suggests a substantial malabsorption of the sugar. We found no effects of the 2-wk adaptation period on the measured gas exchange variables. Significantly lower fasting plasma insulin and triglyceride concentrations were observed during D-tagatose administration compared with the sucrose period. No effects of D-tagatose on body weight and composition were seen, but the perception of fullness 2.5 h after the sugar load was greater with D-tagatose. In conclusion, this study does not suggest a pronounced thermic effect of D-tagatose, and other mechanisms seem to be required to explain its lack of net energy.