Effects of exercise followed by a low-carbohydrate diet on peak fat oxidation and mitochondrial coupling control and efficiency in healthy trained men
Study Details
This randomised crossover study examined how manipulating muscle glycogen through glycogen-depleting exercise followed by a high- or low-carbohydrate diet affected peak fat oxidation, Fatmax and mitochondrial efficiency in 10 trained men 🔍
The high-CHO diet provided ~7.4 g/kg/day, while the low-CHO diet provided ~0.8 g/kg/day 🍞
Key Findings
📉 Muscle glycogen fell by 30.5% after depletion + high CHO, but by 69.3% after depletion + low CHO
↔️ Muscle glycogen was therefore ~56% lower in the low-CHO condition
🔥 Peak fat oxidation increased by 24% after depletion + high CHO, from 0.37 → 0.46 g/min
🚀 With depletion + low CHO, peak fat oxidation increased by ~90%, from 0.39 → 0.74 g/min
📈 Peak fat oxidation was consequently ~61% higher with low versus high carbohydrate availability
🎯 Fatmax shifted from ~41% → 56% VO₂peak in the low-CHO condition, meaning maximal fat oxidation occurred at a substantially higher exercise intensity
🧬 Muscle glycogen was strongly negatively associated with peak fat oxidation (r = −0.81)
🩸 Plasma free fatty acids were strongly positively associated with peak fat oxidation (r = 0.79)
⚙️ Despite these large changes in fuel use, mitochondrial coupling efficiency and respiratory control were unchanged
🫁 VO₂peak was also unchanged between conditions
⚠️ Maximum power fell by ~6.7% after the low-CHO intervention, suggesting greater fat oxidation does not automatically translate into better high-intensity performance
🧩 The intervention altered glycogen, carbohydrate, fat, protein, glucose, insulin and FFA availability simultaneously, so the effect cannot be attributed to glycogen alone
Conclusion
Reducing carbohydrate availability after glycogen-depleting exercise can dramatically increase peak fat oxidation and shift Fatmax to higher intensities, but this metabolic shift occurs without improved mitochondrial efficiency and may come at a cost to maximal power output ✅
Reference
https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP291697
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