Mind & Matter Carbohydrates vs Ketosis in Exercise, Fatigue & Sports Science | Andrew Koutnik | 271
Jan 2, 2026
02:10:26
Deep dive into how ketogenic diets and carbohydrate intake effect exercise performance, and misconceptions in sports nutrition.
TOPICS DISCUSSED:
- Insulin as a powerful metabolic hormone: regulates nutrient storage across tissues, overriding others like glucagon to promote fat and glucose storage during abundance.
- Glucagon & GLP-1 roles in metabolism: Glucagon mobilizes liver glucose during scarcity; GLP-1, amplified in drugs like Ozempic, suppresses hunger but originated as a diabetes treatment.
- Transition to ketosis in fasting or low-carb diets: Low insulin enables fat breakdown into ketones for brain fuel, allowing survival for weeks without food, with adaptation taking about four weeks.
- Hypoglycemia vs. glycogen depletion: Low blood sugar causes fatigue and irritability due to brain energy deficit, while muscle glycogen levels do not directly limit performance.
- Ketogenic diets & exercise performance: Studies show no difference in endurance after adaptation, with some athletes performing better on low-carb due to enhanced fat oxidation.
- High-carb diets in athletes: In one study, about 30% developed prediabetes-like fasting glucose elevations, linked to total carb intake, despite leanness and fitness.
- Misconceptions in sports nutrition: Guidelines recommend 60-90g carbs/hour, but evidence shows 10g suffices to maintain blood sugar and performance, avoiding insulin spikes that impair fat use.
- Individual variability in diet response: Athletes vary in optimal fuel sources; it’s possible to by athletic and lean but also metabolically unhealthy.
PRACTICAL TAKEAWAYS:
- For workouts over ~60 minutes, consume ~10g carbs per hour (e.g., a third of a banana) to maintain blood sugar and prevent fatigue, regardless of overall diet.
- Allow at least four weeks for adaptation when trying a ketogenic diet, enabling the body to fully transition to the ketogenic state.
- Monitor personal responses to carb intake, as high levels can elevate fasting glucose even in fit individuals; consider lower-carb options if experiencing metabolic issues.
- Prioritize metabolic flexibility through varied diets or fasting periods to improve energy stability, but consult resources for proper formulation to support health.
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