Most athletes are told the same basic rule: the harder you train, the more carbs you need. But Dr. Andrew Koutnik argues the science is more complicated.

In this episode, Mike Haney talks with Dr. Koutnik about how the body fuels exercise, why muscle glycogen may not explain “hitting the wall” as neatly as many people think, and why blood glucose, brain energy, insulin, and metabolic flexibility may matter more than conventional sports nutrition advice suggests.

They discuss whether athletes really need 60, 90, or even 120 grams of carbs per hour, why some athletes may perform well on far less, and how to think about fueling as an individual experiment rather than a universal rule. Because apparently even “eat sugar while running” was too simple for human physiology to leave alone.

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🎙️ About the Guest:

Dr. Andrew Koutnik is a Visiting Research Scientist at the Florida Institute for Human and Machine Cognition, studying nutrition, metabolism, Type 1 diabetes, and human performance. He earned his PhD in medical sciences from the University of South Florida and has worked with groups including NASA and the Department of Defense.

📍What Dr. Andrew Koutnik & Mike Haney discussed:

00:42 Why carbs became central to sports nutrition
05:30 How the body uses carbs, fat, ketones, and lactate for fuel
13:45 Exercise, insulin sensitivity, and blood glucose
21:20 Why muscle glycogen may not explain performance limits
31:00 What “hitting the wall” may really mean
39:15 The case for lower-carb fueling strategies
48:30 Why more carbs don’t always mean better performance
58:00 The problem with 90–120 grams of carbs per hour
1:08:30 How athletes can test fueling for themselves
1:17:00 What this means for everyday exercisers and marathoners

🔗 Helpful Links:Watch the conversation: ⁠https://youtu.be/FfomxfyCchw

Study discussed: Carbohydrate Ingestion on Exercise Metabolism and Physical Performancehttps://academic.oup.com/edrv/article/47/2/191/8432248Related paper: Substrate Oxidation Does Not Influence Middle Distance Running Performancehttps://www.mdpi.com/2072-6643/17/17/2771

Find us on YouTube: https://youtube.com/levelshealth?sub_confirmation=1

📲 Connect:Connect with Dr. Andrew Koutnik: https://andrewkoutnik.com/X: https://x.com/AKoutnikInstagram: https://www.instagram.com/andrewkoutnikphd/Google Scholar: https://scholar.google.com/citations?hl=en&user=2BzUjqkAAAAJ

👋 Who we are:

Levels helps you understand your metabolic health with personalized data, expert guidance, and tools that connect your daily choices to measurable changes in your body. Our goal is to help you make better decisions about food, exercise, sleep, and long-term health.