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

2026-07-27

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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

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.

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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)

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Simon Hill, MSc, BSc (Hons)