In this episode, Dr. Iñigo San Millán, Assistant Professor at the University of Colorado School of Medicine, explains the crucial role of mitochondrial function in everything from metabolic health to elite exercise performance. Iñigo provides a masterclass into the many different energy system pathways, the various fuel sources (including the misunderstood lactate), the six zones of exercise training, and the parameters he uses to measure metabolic health. Additionally, he highlights the power of zone 2 training in its ability to act as a powerful diagnostic tool, and perhaps more importantly as a treatment for mitochondrial and metabolic dysfunction. We discuss: Iñigo’s background in sports and decision to focus on education [7:15]; Explaining the various energy systems and fuels used during exercise [14:45]; Iñigo qualifies energy systems into six training zones [26:00];  Lactate is an important fuel source [33:00]; Zone 2 training—physiologic characteristics, fuel sources, lactate, and the transition into zone 3 [40:30]; Using blood lactate levels (and zone-2 threshold) to assess mitochondrial function [47:00]; Accessing mitochondrial function by looking at one’s ability to utilize fat as fuel (with an RQ test) [55:00]; Athletes vs. metabolically ill patients—mitochondria, fat oxidation, muscle glycogen capacity, “fat droplets”, and more [1:00:00]; Physiologic characteristics of zone 3, zone 4, and the lactate threshold [1:20:00]; Fueling exercise—dietary implications on glycolytic function [1:30:30]; Relationship between exercise and insulin sensitivity (and what we can learn from studying patients with type 1 diabetes) [1:46:30]; Metformin’s impact on mitochondrial function, lactate production, and how this affects the benefits of exercise [2:04:15]; Raising awareness for risk of “double diabetes” [2:15:00]; How to dose zone 2 training, and balancing exercise with nutrition [2:18:00]; Proposed explanation of the Warburg Effect: Role of lactate in carcinogenesis [2:27:00]; Doping in cycling, and the trend towards altitude training [2:39:15] and; More. Learn more: https://peterattiamd.com/ Show notes page for this episode: https://peterattiamd.com/inigosanmillan Subscribe to receive exclusive subscriber-only content: https://peterattiamd.com/subscribe/ Sign up to receive Peter's email newsletter: https://peterattiamd.com/newsletter/ Connect with Peter on Facebook | Twitter | Instagram.