The effect of a short-term ketogenic diet on exercise efficiency during graded exercise in healthy adults

Objective We examined the effects of short-term KD on exercise efficiency and hormonal response during and after the graded exercise testing. Methods Fourteen untrained healthy adults (8 males, 6 females, age 26.43.1 [SD] years; BMI 24.84.6kg/m(2); peak VO(2)max 54.0 +/- 5.8ml/kg FFM/min) completed 3-days of a mixed diet (MD) followed by another 3-days of KD after 3-days of washout period. Upon completion of each diet arm, participants underwent graded exercise testing with low- (LIE; 40% of VO(2)max), moderate- (MIE; 55%), and high-intensity exercise (HIE; 70%). Exercise efficiency was calculated as work done (kcal/min)/energy expenditure (kcal/min). Results Fat oxidation during the recovery period was higher in KD vs. MD. Despite identical workload during HIE, participants after having KD vs. MD showed higher energy expenditure and lower exercise efficiency (10.1 +/- 0.7 vs. 12.5 +/- 0.3%, p<.01). After KD, free fatty acid (FFA) concentrations were higher during MIE and recovery vs. resting, and beta-hydroxybutylate (BOHB) was lower at HIE vs. resting. Cortisol concentrations after KD was higher during recovery vs. resting, with no significant changes during graded exercise testing after MD. Conclusions Our data suggest that short-term KD is favorable to fat metabolism leading increased circulating FFA and BOHB during LIE to MIE. However, it is notable that KD may cause 1) exercise inefficiency manifested by increased energy expenditure and 2) elevated exercise stress during HIE and recovery. Trial registration: KCT0005172, International Clinical Trials Registry Platform.

Automated summary

This study found that short-term ketogenic diet may enhance fat metabolism but could lead to decreased exercise efficiency and increased exercise stress.