The ketohexose
D-tagatose is readily oxidized but contributes poorly to
lipid deposition. We therefore examined whether this
sugar contributes to energy requirements by determining its net metabolizable energy value in rats. All substrate-induced energy losses from
D-tagatose, with
sucrose as reference standard, were determined as a single value accounting for the sum of the energy losses to feces, urine, gaseous
hydrogen and methane and substrate-induced thermogenesis. A randomized parallel design involving two treatment periods (adaptation to
D-tagatose and subsequent energy balance) and two control groups (to control for treatment effects in each period) was used. Rats consumed 1.8 g test
carbohydrate daily as a supplement to a basal diet for a 40- or 41-d balance period after prior adaptation for 21 d. Growth,
protein and
lipid deposition were unaffected by supplementary gross energy intake from
D-tagatose compared with an unsupplemented control, but
sucrose significantly (P < 0.05) increased all three. Based on the changes induced in
protein and fat gain during the balance period it was calculated that
D-tagatose contributed -3 +/- 14% of its heat of combustion to net metabolizable energy, and therefore this ketohexose effectively has a zero energy value.
D-Tagatose would potentially be helpful in
body weight control, especially in diabetic subjects because of its antidiabetogenic effects.