Episode 4 : [Science vs. Myth #2] Fasted Cardio SCAM: Does It Burn More Fat or Just Your Muscle? 🏋️

Episode 4 : [Science vs. Myth #2] Fasted Cardio SCAM: Does It Burn More Fat or Just Your Muscle? 🏋️💬 Got a question or feedback? Write us at: [email protected]: Is fasted cardio the secret to becoming an efficient fat-burning machine, or are you just cannibalizing muscle and wrecking your performance for a myth? This episode dives into the real physiology of training on an empty tank. We explain the "metabolic dimmer switch" that balances carbohydrates—your high-octane fuel—and fat. In a fasted state, low insulin removes the brakes on fat release, while hormones like adrenaline and cortisol accelerate its breakdown. But there's a hidden cost: this stress response also triggers gluconeogenesis, forcing your body to break down precious muscle protein to create glucose, which can paradoxically cause a post-exercise blood sugar spike. The true goal isn't just fat burning; it's achieving metabolic flexibility—the ability to efficiently use both fuel sources when performance demands it. The science is clear: meta-analyses show that fasted training impairs performance in any session lasting over 60 minutes and offers zero advantage for shorter ones. The only strategic use is within a "Train Low, Compete High" framework—reserving it for a maximum of one to two short, low-intensity Zone 2 sessions per week to stimulate adaptation, without compromising key workouts. For female athletes, the risks are even greater; fasted training is a significant behavioral risk factor for Low Energy Availability (LEA) and REDs, linked to a 1.61 times higher rate of bone injuries. We also look at ultra-endurance legend Yiannis Kouros, who shattered records by fueling on a diet that was over 95% carbohydrates—not fat.Keywords: fasted cardio, metabolic flexibility, fat oxidation, glycogen, train low compete high, endurance training, muscle protein breakdown, red-s, female athlete🎙️ Lactate, the podcast that deciphers science to improve your performance.Key references :Aird, T. P., Davies, R. W., & Carson, B. P. (2018). Effects of fasted vs fed-state exercise on performance and post-exercise metabolism: A systematic review and meta-analysis. Scandinavian Journal of Medicine & Science in Sports, 28(5), 1476-1493. https://pubmed.ncbi.nlm.nih.gov/29315892/Vieira, A. F., Costa, R. R., Macedo, R. C. O., Coconcelli, L., & Kruel, L. F. M. (2016). Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: A systematic review and meta-analysis. British Journal of Nutrition, 116(7), 1153-1164. https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/effects-of-aerobic-exercise-performed-in-fasted-v-fed-state-on-fat-and-carbohydrate-metabolism-in-adults-a-systematic-review-and-metaanalysis/0EA2328A0FF91703C95FD39A38716811Williamson, E., & Moore, D. R. (2021). A Muscle-Centric Perspective on Intermittent Fasting. Frontiers in Nutrition, 8. https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2021.640621/fullZouhal, H., Saeidi, A., Salhi, A., Li, H., et al. (2020). Exercise Training and Fasting: Current Insights. Sports Medicine, 50, 917–941. https://pmc.ncbi.nlm.nih.gov/articles/PMC6983467/Mountjoy, M., et al. (2023). 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 57(17). https://stillmed.olympics.com/media/Documents/Athletes/Medical-Scientific/Consensus-Statements/REDs/BJSM-IOC-consensus-statement-on-Relative-Energy-Deficiency-in-Sport-REDs.pdfBurke, L. M., et al. (2024). Prevalence of reducing carbohydrate intake and fasted training in elite endurance athletes and association with bone injury. Medicine & Science in Sports & Exercise, 56(6). https://pmc.ncbi.nlm.nih.gov/articles/PMC11369321/Voices generated by artificial intelligence from the scientific report produced by the Lactate team.