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. BACK-TO-SCHOOL SALE! For a limited time, save 40% sitewide at ketogenicgirl.com with code BACKTOSCHOOL40, including the Protein-Sparing Modified Fasting Library, ToneLUX Red Light Therapy Collection, and Tone Breath Ketone Analyzer. 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 • Adjusting carbohydrates to support your training performance • Protein-sparing modified fasting and the considerations around more aggressive calorie deficits • Why stubborn lower-body fat can be especially frustrating for women • Protein and resistance training: their roles in preserving lean mass while dieting • Building aerobic fitness to support metabolic flexibility over time • Heat, cold exposure, and Mike's broader framework of physiologic flexibility • Lactate as a valuable fuel and the emerging interest in lactate supplements • Tracking performance alongside the scale—and keeping maintenance in mind from the beginning I loved Mike's emphasis on building a body that can perform well while you work toward your body-composition goals. This episode is full of thoughtful distinctions to help you better understand the science behind fat loss! Connect with Dr. Mike T. Nelson: Instagram: @drmiketnelson Explore his newsletter for more on body composition, performance, and metabolic flexibility. Special offers mentioned in this episode: Save 40% sitewide at ⁠KetogenicGirl.com with code BACKTOSCHOOL40, including the Protein-Sparing Modified Fasting Library and Tone Device. Australia and New Zealand listeners: save 75% during the warehouse moving sale with code WAREHOUSE75. If you enjoyed this episode, please subscribe, leave a rating or review, and share it with a friend. Your support helps us continue bringing you conversations with leading researchers and experts in protein, metabolic health, and body composition. Follow @ketogenicgirl and @optimalproteinpodcast on Instagram, and join the Optimal Protein Podcast Facebook group for more discussion. The content provided in this podcast is for informational purposes only and should not be construed as medical advice. Consult with a healthcare professional before making significant changes to your diet, supplements, or exercise regimen.