Carbohydrate ingestion eliminates hypoglycemia and improves endurance exercise performance in triathletes adapted to very low- and high-carbohydrate isocaloric diets
Study Details
This randomised crossover study examined whether minimal carbohydrate during exercise could improve endurance after 6 weeks on very-low- or high-carbohydrate diets in 10 trained male triathletes 🔍
Athletes completed 6 weeks of a very-low-carbohydrate/high-fat diet (~40 g CHO/day) and 6 weeks of a high-carbohydrate/low-fat diet (~380 g/day) 🥑
After each diet, they cycled to exhaustion at 70% VO₂max following a >15 h overnight fast 🚴
During exercise, athletes consumed placebo or only ~10 g carbohydrate/hour 🍬
Key Findings
↔️ Time-to-exhaustion performance was not significantly different between diets
📈 10 g/hr increased time to exhaustion by ~22%, equivalent to ~19 minutes, regardless of habitual diet
🩸 Without carbohydrate, exercise-induced hypoglycaemia occurred after both diets; 10 g/h completely prevented it
🔥 The low-carb diet produced greater fat oxidation and lower carbohydrate oxidation, yet this did not translate into poorer performance
🧠 The authors argue that maintaining blood glucose may therefore have contributed more to the benefit than simply increasing carbohydrate oxidation
⏱️ Continuous glucose monitoring showed lower glucose during the first weeks of the low-carb diet, but values normalised after ~4 weeks, alongside stabilisation of blood ketones
⚠️ Muscle and liver glycogen were not directly measured
Conclusion
A small amount of carbs may meaningfully delay fatigue during prolonged fasted exercise by maintaining blood glucose, but these findings do not show that ~10 g/h is optimal for competition or that higher carbohydrate intakes are unnecessary ✅
Reference
https://pubmed.ncbi.nlm.nih.gov/39786965/
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