Plain language summary
The ketogenic diet (KD) is a high-fat, low-carbohydrate diet that has gained popularity for its potential benefits in weight loss and metabolic health. Despite potential merits of KD on metabolic health, it is controversial whether KD has positive or negative impact on exercise performance and exercise efficiency, and exercise fatigue during endurance exercise. The primary aim of the study was to examine the effects of a short-term KD on exercise efficiency and hormonal responses during and after graded exercise testing. This study was an experimental study involving 14 untrained healthy adults (8 males and 6 females) who followed a mixed diet (MD) for 3 days, a washout period of 3 days, and then a KD for another 3 days. Participants underwent graded exercise testing at low (40% VO2 max), moderate (55% VO2 max), and high-intensity (70% VO2 max) levels. Results: - fat oxidation: higher during the recovery period after KD compared to MD. - energy expenditure: increased during high-intensity exercise after KD, leading to lower exercise efficiency. - hormonal responses: higher free fatty acid concentrations during moderate-intensity exercise (MIE) and recovery after KD. Beta-hydroxybutyrate levels were lower at HIE after KD. Cortisol concentrations were higher during recovery after KD. Authors concluded that a short-term KD enhances fat metabolism, increasing circulating free fatty acid and BOHB during low to MIE. However, it also leads to reduced exercise efficiency and elevated exercise stress during high-intensity exercise and recovery.
Abstract
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 26.4 ± 3.1 [SD] years; BMI 24.8 ± 4.6 kg/m2; peak VO2max 54.0 ± 5.8 ml/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 VO2max), 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.
Methodological quality
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