CARBOHYDRATE OXIDATION BY TRACER USE VERSUS INDIRECT CALORIMETRY

Using a simplified steady state model of in vivo carbohydrate metaboli sm representing various conditions of glucose loading after a fast, we compare true values of carbohydrate oxidation with values calculated by the approaches of Wolfe or of Tappy which are based on the use of i sotopes, using their types of corrections for incomplete recovery of l abelled CO2. These isotopic approaches are shown to be not consistentl y accurate. Also, for the strongly fasted state in which glycogenolysi s is negligible, these isotopic approaches are plainly illogical, plas ma glucose being simply an intermediate in glucogenic amino acid and i n lipid glycerol oxidation.