Acute effects of fasting aerobic exercise on carbohydrate and fat metabolism and utilization in sedentary overweight and obese adults: A pilot study

Purpose: To compare the acute effects of fasting and postprandial aerobic exercise on carbohydrate and fat utilization in sedentary overweight and obese men. Methods: Quantitative, experimental, randomized, crossover design. Seven sedentary, overweight or obese (body mass index [BMI]= 29.3 +/- 1.9 kg/m(2)) adult men (37.9 +/- 2.4 years) performed 60 min of aerobic exercise at 50% of maximal aerobic power both fasting (FASTED) and postprandial (FED). The first exercise type was randomly assigned. We measured the respiratory exchange ratio (RER) by basal indirect calorimetry during and after exercise; glycemia, ketone bodies and capillary lactate at baseline, pre-start, immediately and 40 minutes post exercise were measured in each exercise protocol. Oxidation of carbohydrates and fats was estimated from the RER according to stoichiometric equations. Results: During exercise there were no significant differences in the use of substrates between FASTED and FED. After exercise, only FASTED had an increase (p<0.05) in fat oxidation relative to body (Pre 0.010 +/- 0.006 kJ/min/kg vs Post 0.020 +/- 0.014 kJ/min/kg), carbohydrate oxidation (Pre 0.060 +/- 0.010 kJ/min/kg vs Post 0.070 +/- 0.012 kJ/min/kg), and total energy expenditure (Pre 0.070 +/- 0.017 kJ/min/kg vs Post 0.090 +/- 0.028 kJ/min/kg). There were no differences in FED, nor significant differences between FASTED and FED. Conclusion: Moderate aerobic fasting exercise increases post-session fat and carbohydrate oxidation in overweight and obese men. This could be useful for application in sedentary patients with excess weight.

Automated summary

This study found that moderate aerobic fasting exercise can increase post-session fat and carbohydrate oxidation in overweight and obese men, which may have potential applications for sedentary patients with excess weight.