What if one overlooked molecule could transform the way we think about performance, chronic disease, and ageing? In this episode, I am joined by Dr Iñigo San Millán, exercise physiologist, researcher, and coach to Tour de France champion Tadej Pogačar. Known for his pioneering work on mitochondria and metabolism, Dr San Millán is at the forefront of lactate research, revealing it as a vital fuel and biomarker for human health.
Far from being a waste product, lactate plays a central role in how our bodies produce energy, adapt to exercise, and defend against disease. Together we explore how lactate offers a window into mitochondrial function, what training methods best support its clearance, and why this knowledge has implications far beyond elite sport.
What We Cover
- What lactate really is and why it matters for everyone
- How lactate profiles differ between athletes and those with metabolic disease
- The lactate shuttle and the role of mitochondrial transporters
- Why Zone 2 cardio supports fat oxidation and metabolic flexibility
- How to programme Zone 2, intervals, and strength work into your week
- The impact of diet on mitochondrial health and lactate clearance
- Common critiques of Zone 2 training and the broader implications for longevity
Mitochondrial dysfunction underlies both ageing and chronic disease. By reframing lactate as a fuel and signal, Dr San Millán provides a clear roadmap for better health and performance at any stage of life.
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)
Subscribe and stay connected:
Subscribe to The Proof on YouTube, Apple Podcasts or Spotify to ensure you never miss an episode. And don’t forget to follow me on Instagram and X for more insights and updates.
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.
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.
More about Dr Iñigo San Millán
Dr Iñigo San Millán is a globally recognized expert in physiology, metabolism, and performance science, with nearly three decades of experience optimizing the health and performance of elite athletes, including Tour de France winners and Olympic medalists. As Director of Performance at Athletic Club de Bilbao and a longtime architect of Team UAE Emirates’ dominance in world cycling, including the development of the performance program behind Tadej Pogačar, he has played a key role in shaping modern endurance sports science through a range of groundbreaking scientific and methodological innovations.
A true pioneer, Dr San Millán was the first to measure substrate utilization (fat and carbohydrate oxidation) in competitive athletes over 20 years ago, leading to groundbreaking changes in sports nutrition. He introduced the concept of consuming 80–100 g/h of carbohydrates in endurance events long before it became standard practice and later advanced it to 125 g/h with Pogačar in his first pro season. He also coined the now-ubiquitous term “Zone 2” training nearly 30 years ago, defining training zones based on metabolic parameters like lactate and substrate utilization, now a cornerstone of endurance training worldwide.
Dr San Millán developed the first metabolomics platform used in professional sports and created a novel methodology to indirectly measure mitochondrial function and metabolic flexibility, a tool now applied not only in elite performance but also in clinical settings. His innovations span beyond athletics and into metabolic health, where he is a global authority. His work bridges the gap between high-performance sport and medicine, helping patients with type 2 diabetes, cancer, post-ICU complications, and those focused on longevity optimize their metabolic function.
As the co-author of the Lactagenesis Hypothesis, Dr San Millán has helped reframe the understanding of the Warburg Effect, proposing lactate as a master regulator in cancer biology. His research demonstrates lactate’s role in gene expression, opening new avenues for diagnostics and therapeutics in oncology.
An adjunct professor and published scientist, Dr San Millán continues to advise top global organizations and drive innovation at the intersection of performance, health, and medicine.
