Peter Attia MD#85 – Iñigo San Millán, Ph.D.: Mitochondria, exercise, and metabolic health
At a glance
WHAT IT’S REALLY ABOUT
Mitochondrial Function, Zone 2 Training, Lactate, and Metabolic Disease Explained
- San Millán explains his six-zone training framework tied to muscle fiber recruitment and fuel use, with zone 2 as the intensity where fat oxidation peaks and slow-twitch mitochondria are most stimulated.
- He argues lactate is a fuel and signaling molecule rather than a waste product, and that blood lactate at a given power reflects how well the muscle's mitochondria can clear it.
- A study with George Brooks found world-class cyclists, recreational athletes and people with type 2 diabetes reach their zone 2 limit at very different power outputs, supporting the use of zone 2 testing as an indirect measure of mitochondrial function.
- The conversation covers type 1 diabetes research, non-insulin-dependent glucose uptake during exercise, and how cool-downs and lower insulin dosing can reduce post-exercise glucose swings.
- Attia describes his metformin experiment, in which lactate dropped as he cut his dose, and both speakers explore possible links among metformin, mitochondrial function and lactate, and the role of lactate in cancer signaling.
IDEAS WORTH REMEMBERING
5 ideasElite endurance athletes serve as a model of metabolic health.
San Millán says their mitochondria are the healthiest on the planet, so understanding this perfection helps explain the dysfunction seen in type 2 diabetes and may inform diagnostics, therapeutics and prevention.
Zone 2 is where mitochondrial training and fat burning peak.
It coincides with Fatmax and heavily stimulates slow-twitch fibers before fast-twitch recruitment begins, with blood lactate typically around 1.5 to 2 millimolar.
Lactate is a fuel and signal, not mere waste.
San Millán says slow-twitch mitochondria oxidize lactate made in fast-twitch fibers, so fit athletes can produce lactate yet keep it from accumulating in blood, while the burning sensation comes from associated hydrogen ions.
Zone 2 power output works as an indirect mitochondrial function test.
In the Brooks collaboration, pairing fat oxidation and lactate curves distinguished athletes, recreational riders and people with diabetes, and correlations were in the nineties; muscle biopsies are planned to confirm the mechanisms.
Muscle contraction can move glucose into muscle without insulin.
Contraction translocates GLUT4 transporters to the muscle surface, which is why Attia's glucose falls during zone 2, and San Millán has applied this with type 1 diabetics through reduced insulin dosing and post-exercise cool-downs.
WORDS WORTH SAVING
5 quoteswe need to understand what perfection is in order to understand imperfection.
— Dr. Iñigo San Millán
lactate is the most important, if not the most important, uh, fuel for the body.
— Dr. Iñigo San Millán
Every cell in the body produces lactate, and pretty much every cell in the body consumes lactate.
— Dr. Iñigo San Millán
I always think there's not such state as being pre-pregnant or pregnant. You're pregnant or you're not.
— Dr. Iñigo San Millán
I'm not sure how you can trust me if I'm telling you about something when you know I'm being paid by the company that makes it to tell you about it.
— Peter Attia
High quality AI-generated summary created from speaker-labeled transcript.
