Lactate: The Key to Metabolic Health, Mitochondria, and Longevity | Dr Iñigo San Millán

In this episode I am joined by Dr Iñigo San Millán, exercise physiologist, researcher, and coach to Tour de France champion Tadej Pogačar. His work places lactate at the centre of human health, showing it as a fuel and biomarker rather than a waste product. We discuss how lactate offers a new lens on mitochondrial health, what Zone 2 training really achieves, and why these insights apply to both elite athletes and anyone seeking longevity. What We Cover Lactate myths and the truth about its role in energy Differences between athletic and diseased lactate profiles Zone 2 training and mitochondrial health Balancing training methods for metabolic flexibility Diet, lactate, and critiques of Zone 2 This conversation shows why understanding lactate could be key to improving performance, preventing disease, and ageing well. You can connect with Dr Iñigo San Millán on Instagram and Twitter, where he shares insights on exercise physiology, metabolism, and performance. Follow along to learn more about his research and practical applications for both athletes and everyday health. Understanding Lactate as a Biomarker and Signalling Molecule (00:00) Historical Misconceptions About Lactate and Fatigue (04:03) How the Body Uses Lactate as a Fuel Source (06:09) Lactate in Health, Metabolic Function, and Disease (10:25) Exercise, Lactate Dynamics, and Energy Balance (16:39) What Research Reveals About Lactate and Mitochondrial Function (19:03) Exercise Prescription and Training Zones Explained (26:20) High-Intensity Exercise: What Happens to Lactate Levels? (37:87) VO₂ Max, Mitochondria, and Aerobic Fitness (45:02) Supporting Mitochondrial Function for Disease Prevention (48:37) Designing Exercise Programmes for Longevity and Healthspan (51:19) Resistance Training and Its Impact on Metabolic Health (1:00:10) How Diet and Exercise Influence Mitochondrial Function (01:04:42) Is Zone Two Training Really the Key to Endurance? (01:10:39) Final Reflections on Lactate, Training, and Metabolic Adaptation (01:19:47) 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. Function Health Take charge of your health with advanced blood testing and personalised insights. Function Health provides a practical solution to track key health markers such as cholesterol, blood sugar, and more. For the first 1,000 listeners, new members get a $100 credit when signing up. Head to functionhealth.com/simonhill to claim your credit. Only available to those living in the United States. Momentous My go-to supplement brand for protein and creatine is Momentous. Use code LIVINGPROOF for up to 35% off your first order at livemomentous.com. IM8 With 92 nutrients, including Vitamin B12, Iodine, Selenium and Vitamin D, in highly absorbable forms, IM8 Daily Essentials is the perfect all-in-one daily multi-vitamin to ensure you meet your daily micronutrient needs. 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 Eight Sleep Upgrade your sleep with the Pod 5 Ultra by Eight Sleep. Clinically validated to deliver up to 1 extra hour of quality sleep per night through temperature control and biometric tracking. Use code THEPROOF for $350 off at eightsleep.com/theproof. Try it risk-free for 30 days, with worldwide shipping. 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