title: Method for computing the oxidation of two 13C-substrates ingested simultaneously during exercise.
abstract: This study presents a method for computing the respective amounts of two simultaneously ingested exogenous substrates (A and B) that are oxidized during a period of prolonged exercise by use of 13C labeling. This method is based on the observation that the total volume of 13CO2 produced (V13CO2tot) is the sum of 1) V13CO2 arising from the oxidation of endogenous substrates (V13CO2endo), 2) V13CO2 arising from the oxidation of substrate A (V13CO2A), and 3) V13CO2 arising from the oxidation of substrate B (V13CO2B). The equation, V13CO2tot = V13CO2endo+V13CO2A+V13CO2B, with three unknowns, can be solved from the results of three experiments conducted under the same conditions but with at least two values for the isotopic composition of A and B. This method has been used on five healthy male subjects to compute the amounts of glucose and fructose oxidized when a mixture of 15 g of glucose and 15 g of fructose is ingested (in 300 ml of water) over 60 min of cycle ergometer exercise at 65% of maximal O2 uptake. Results from three experiments indicated that 9.8 +/- 3.1 and 5.7 +/- 2.1 g of glucose and fructose, respectively, were oxidized. The total amount of exogenous carbohydrates oxidized (15.5 +/- 4.3 g) is in agreement with the oxidation rates of exogenous glucose computed in similar conditions when 30 g of glucose were ingested (13 g; Péronnet et al. Med. Sci. Sports Exercise 25: 297-302, 1993). The difference between the oxidation rates of exogenous glucose and fructose is also in line with data from the literature.
authors.affiliation: Département d'éducation physique, Université de Montréal, P.Q., Canada.
authors.forename: F
authors.initials: F
authors.lastname: Péronnet
authors.forename: E
authors.initials: E
authors.lastname: Adopo
authors.forename: D
authors.initials: D
authors.lastname: Massicotte
authors.forename: G R
authors.initials: GR
authors.lastname: Brisson
authors.forename: C
authors.initials: C
authors.lastname: Hillaire-Marcel
mesh_terms: D000328:Adult; D002247:Carbon Isotopes; D004435:Eating; D004734:Energy Metabolism; D005632:Fructose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D008297:Male; D008954:Models, Biological; D010084:Oxidation-Reduction; D005082:Physical Exertion
chemical_list: D002247:Carbon Isotopes; D005632:Fructose; D005947:Glucose