Effects of overnight fasting on body fat oxidation during aerobic exercise among healthy men

Abstract

The current global obesity pandemic has become one of the main public health concern. By following the recommended exercise guidelines, fat oxidation may still be inadequate for those who wish to achieve a desirable body mass index. This study investigated the effects of overnight fasting on body fat oxidation during aerobic exercise (AE). It was hypothesized that after a night of fasting, fat oxidation is higher when an individual performed AE in the fasted state as compared to those who exercised in the fed state. 10 healthy men completed two trials in a randomized crossover design (Age 24 ± 0.7 years; Height 172.6 ± 5.7 cm; Body Mass 68.5 ± 7.6 kg; Body Mass Index 23.4 ± 2.4 kg/m2; Maximum Oxygen Consumption 39 ± 5.1 ml/kg/min) and performed an incremental fat oxidation test fasted (CON) or fed with a standardized breakfast (EXP) following an overnight fast of 12 hours. The submaximal fat oxidation test consisted of 6 stages with the workload corresponding to 30%, 40%, 50%, 60%, 70% and 80% of the participants’ maximal oxygen consumption. A two-way ANOVA was used to find out if there were significant differences in fat oxidation, respiratory exchange ratio (RER), rate of perceived exertion (RPE) and heart rate (HR) between CON and EXP. Significance for all tests was set at p < 0.05. Results showed no significant differences in fat oxidation (p = .710), RER (p =.482) and HR (p =.974) between CON and EXP. RPE was significantly higher in CON than EXP (p = .002). In summary, this present study suggests that performing aerobic exercise in the fasted state will not elicit higher fat oxidation as compared to exercising in the fed state.