The metabolizable energy value of Polydextrose in a mixed diet fed to rats

The digestible energy (DE) and metabolizable energy (ME) values of a commercial Polydextrose product and the polymer that it contained were determined by metabolic energy balance in male Wistar rats and compared with values obtained by radiochemical balance using a radiochemical analogue. The energy values of the whole preparations and of the polymer fractions were estimated. In the energy-balance study of 6 d duration, 100 g maize starch/kg control diet were replaced by Polydextrose to provide a test diet. Polydextrose had no significant effects on food intake, body-weight gain, digestibility of nitrogen and N retention but significantly increased the water consumption to 143% of the control value (P less than 0.05) and the water content of fresh faecal pellets from 548 (SE 10) to 646 (SE 15) g/kg wet weight (P less than 0.01). By energy balance the DE in the Polydextrose product and in the polymer that it contained were 13.5 and 12.8 (SE 1.9) kJ/g respectively. The corresponding ME values were 12.7 and 12.1 (SE 1.8) kJ/g respectively. These values were higher (P less than 0.05) than the corresponding values obtained by the radiochemical balance procedure: DE 8.8 and 8.6 (SE 0.4) kJ/g polymer respectively and ME 8.0 and 7.8 (SE 0.5) kJ/g polymer respectively. These findings indicate relatively high energy values for Polydextrose by comparison with previously published values and illustrate a potential difficulty when using energy values obtained by certain radiochemical methods to estimate the energy values of a mixed diet given to rats. Several alternative explanations of the discrepancies are advanced.