Burning Fat vs. Losing Fat: Metabolic Flexibility Explained with Dr. Mike T. Nelson

Does burning more fat for fuel mean you're actually losing more body fat? And if you're in ketosis, does that mean the fat you're burning is coming from your body—or from the food you just ate?

Today on the Optimal Protein Podcast, I'm joined by Dr. Mike T. Nelson to unpack this important distinction and explore what metabolic flexibility really means for fat loss, muscle preservation, and performance.

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Mike holds a PhD in exercise physiology and a master's degree in mechanical engineering with a focus on biomechanics. In this fascinating conversation, we explore your body's ability to use both carbohydrates and fat, switch between them, and adapt to different demands.

We discuss why burning more fat during a workout doesn't necessarily translate into greater body-fat loss, why calorie balance still matters, and how your nutrition and training can work together to support body recomposition. I also share my own experience gaining weight on keto despite high ketone readings—and what that taught me about dietary fat versus stored body fat.

In this episode, we discuss:

• The three components of metabolic flexibility—and why using carbohydrates effectively matters, too

• Burning fat versus losing fat: the distinction that can change how you approach your goals

• How insulin and fuel availability influence what your body burns

• Why higher ketone readings don't necessarily mean greater body-fat loss

• Fasted cardio: what the research suggests and where questions remain

• Long-term keto and the potential tradeoffs for high-intensity exercise