The Science of Metabolic Flexibility, Zone 2, and Reversing Diabetes | A Masterclass

Metabolic dysfunction rarely announces itself. We tend to think of metabolic health as a line you cross the day you are diagnosed with type 2 diabetes, but the decay usually begins years earlier, at the level of the cell. In this masterclass I bring together Dr Iñigo San Millán, Dr Alan Flanagan, Dr Kevin Hall, Dr Robert Eckel, Professor Roy Taylor, and Dr Christos Mantzoros to explain what metabolic flexibility is, why your mitochondria sit at the centre of it, and what you can actually do about it. What We Cover Why lactate is a fuel and a signal, not a waste product, and our best non-invasive window into mitochondrial function Whether a calorie really is a calorie, and what the controlled chamber studies found The twin cycle hypothesis, and why type 2 diabetes is more reversible than we were taught The personal fat threshold, and why a normal BMI can still hide a problem Whether sugar or saturated fat does more to drive fat in the liver Why Zone 2 earns its reputation, and how much of it you actually need Metabolic health is not fixed, and it is rarely too late to move in a better direction. I hope this conversation gives you a clearer picture of what is happening beneath the surface, and a few levers you can start pulling today. To learn more from the experts featured in this masterclass, you can follow Dr Iñigo San Millán on Instagram and Twitter, explore Professor Roy Taylor's work on type 2 diabetes remission at Newcastle University, read more from Dr Kevin Hall at kevinhallphd.com or on LinkedIn, and find Dr Alan Flanagan on Instagram and through Alinea Nutrition. The masterclass also features insights from Dr Robert Eckel and Dr Christos Mantzoros. If you are enjoying The Proof, please take a moment to rate and review the show on Apple Podcasts. It genuinely helps more people find these conversations. The 81-Year-Old Who Reversed 30 Years of Damage (00:00) What Metabolic Health Actually Means Now (01:57) Why Mitochondria Decide Your Disease Risk (06:01) What Is Metabolic Flexibility? (12:47) Hepatic Fat Oxidation and the Sex Difference (15:20) Is a Calorie Really a Calorie? (18:29) You Can Be Sick Before You're Diagnosed (28:41) Why Lactate Is the Biomarker to Watch (29:20) Lactate Is Not a Waste Product (31:03) Is Lactic Acid Burn a Myth? (36:42) Why Athletes Clear Lactate and You Don't (40:34) When High Lactate Predicts Death (43:01) The Study That Found Damage in Healthy People (47:13) The Lactate Test That Beats Blood Sugar (54:31) Training Zones 1 to 6 Explained by Fuel (58:50) Why Zone 2 Builds Mitochondria Best (1:09:18) How to Know You're in Zone 2 Without a Lab (1:16:50) Is 150 Minutes a Week Enough? (1:23:39) Why You Still Need High Intensity Training (1:28:10) What Obesity Research Got Wrong (1:31:44) The Twin Cycle Hypothesis of Type 2 Diabetes (1:35:04) Your Personal Fat Threshold Explained (1:42:26) Why Some People Store Fat Safely (1:45:45) Why BMI Fails as a Health Measure (1:51:29) Sugar or Saturated Fat: What Drives Liver Fat? (1:55:07) 15kg Weight Loss and Diabetes Remission (2:01:05) Does Weight Loss Really Destroy Muscle? (2:04:39) Why Exercise Alone Doesn't Drop Weight (2:07:05) 3 Tests That Reveal Your Metabolic Health (2:11:14) What Blue Zones Get Right About Movement (2:17:40) Want to support the show? The best way to support the show is to use the products and services offered by our sponsors. To check them out and enjoy great savings, visit theproof.com/friends. You can also support the show by leaving a review on the Apple Podcast app and sharing your favourite episodes with friends and family. This episode is brought to you by: 38TERA Consider 38TERA's DMN prebiotic supplement a daily multivitamin for your gut. Formulated by yours truly and gastroenterologist Dr Will Bulsiewicz. Use code THEPROOF for a discount at checkout. 38Tera ships to the United States, Australia, and New Zealand. Function Health Take charge of your health with advanced blood testing and personalised insights. Function Health offers a practical way to track key health markers such as cholesterol, blood sugar, and more. 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IM8 is offering an exclusive 10% off your first order with a free welcome kit when you enter the promo code SIMON at checkout on im8health.com. IM8 ships to 27 countries including the U.S., Canada, the U.K., Australia, and many regions across Europe, Asia, and South America. WHOOP Whoop, the most advanced fitness and health wearable available. Your personalised fitness and health coach to recover faster, sleep better, and train smarter. Claim your first month free on join.whoop.com/simon. Whoop ships to 56+ international markets, including the US, Canada, most of Europe, Australia, New Zealand, UAE, Singapore, and parts of Asia. Simon Hill, MSc, BSc (Hons) Creator of theproof.com Host of The Proof with Simon Hill Author of The Proof is in the Plants Subscribe & Connect: YouTube Apple Podcasts Spotify Instagram: @simonhill Twitter: @theproof Facebook: The Proof with Simon Hill Nourish your gut with my Plant-Based Ferments Guide and download my Two-Week Meal Plan.