The Metabolic Oxidation of Glucose: Thermodynamic Considerations for Anaerobic and Aerobic Energy Expanditure

Document Type

Article

Publication Date

8-2008

Publication Title

Journal of Exercise Physiology Online

Keywords

Metabolism, Glycolysis, Bioenergetics, Oxygen Uptake, Oxygen Debt

Abstract

Scott CB, Djurisic ZM. The Metabolic Oxidation of Glucose: Thermodynamic Considerations for Anaerobic and Aerobic Energy Expenditure. JEPonline 2008;11(4):34-43. When estimated per liter of oxygen uptake, the energy expenditure equivalent of fat oxidation is 19.6 kJ, for glucose oxidation 21.1 kJ. The purpose of this manuscript is to answer the question, why the 1.5 kJ (7%) difference? Our answer acknowledges the slight variation in the enthalpy of molecular bond formation that is found as different fuels undergo oxidation. However, this difference usually varies by ±5%. When expressed per liter of oxygen consumed, we interpret the slightly larger 7% difference (1.5 kJ) found between the heat produced by fat and glucose oxidation in terms of the inefficiency of the biochemical pathways that break these two substrates down, in addition to the oxidation of the substrates themselves. Fat oxidation is entirely aerobic at 19.6 kJ per liter of oxygen uptake. Complete glucose oxidation has both an anaerobic and aerobic metabolic component. Because both aerobic and anaerobic metabolisms are inefficient (resulting in changes in both heat and entropy), we interpret the 1.5 kJ L-1 O2 difference between fat and glucose oxidation, in part, as being the result of the anaerobic metabolic component in the degradation of glucose. This separation allows for both an estimate of anaerobic and aerobic energy exchange during exercise and, aerobic energy exchange during recovery (excess post-exercise oxygen consumption, EPOC).

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