Interview With Dr. Jason Fung and Gary Taubes
What this video covers
Produced as a lead-in to a CrossFit Health Education webinar, this is a journalist-to-physician conversation: Taubes interviews Toronto nephrologist Dr. Jason Fung about how fasting became a therapeutic tool in Fung’s practice. Taubes discloses his own stake up front: he tried intermittent fasting as an experiment three years earlier, expecting a fad that would pass — and says he owes Fung a debt of gratitude.
Fung’s path started with a paradox he says he couldn’t unsee. Type 2 diabetes is the leading cause of kidney disease, so his clinic filled with diabetics — and the standard treatment, he says, was to prescribe more insulin to lower blood sugar, even though insulin reliably made patients gain weight and everyone agreed that losing weight improves diabetes. His patients hadn’t changed, he says — not their willpower, not their exercise. The major difference was that he had given them insulin, and they gained weight. Around 2008–2010, as large studies of that treatment paradigm accumulated, he went back to first principles and concluded the calories framework itself was the problem. He compares it to saying a plane crashed because lift failed to overcome gravity: true, and useless — Wolfgang Pauli’s dismissal, supplied by Taubes, is “not even wrong.” What actually controls calories in and calories out, Fung argues, is hormonal: hunger on one side, basal metabolic rate on the other. And the master hormone is the one he had been prescribing.
The cleanest evidence, in Fung’s telling, is the two-sided experiment medicine runs every day: give insulin and people get fat; take it away — untreated type 1 diabetics — and they are “like sticks.” (Some type 1 patients, he notes, deliberately underdose their insulin to stay thin.) So he built a program around lowering insulin instead: first low-carbohydrate diets, then — because many of his older Toronto patients, raised on rice and noodles, didn’t take to carb-counting — fasting, which he calls far simpler to explain: don’t eat anything until dinner. He recounts the case series he published in BMJ Case Reports: three patients, each with roughly 20 years of type 2 diabetes and about five years on insulin, put on 24-hour fasts three times a week. Between five and 18 days, he says, all three had come off all their insulin; within two months, all were essentially non-diabetic.
Fung is unusually candid about the denominators. Of 100 patients, he estimates, about half won’t try fasting at all; of those who start, roughly half drop out — often, he says, after an endocrinologist or another doctor objects. Of the quarter who fast consistently, he estimates about 80% get better. The dietitians at his hospital, he says, thought he was “completely insane” and wouldn’t sign off on the program; he built it instead with medical researcher Megan Ramos, and says skeptical colleagues came around mainly when shared patients started coming off their medications in front of them.
The back half compares fasting with ketogenic diets — “accomplishing the same thing in two different ways,” in Fung’s phrase. Both work, on his account, by lowering insulin; a study he cites found the ketogenic diet gets about 80% of the way to fasting’s insulin reduction. The open question is mTOR and autophagy: protein stimulates mTOR, which switches off autophagy, the cellular recycling process — so a keto diet that includes protein may not reproduce everything fasting does. But Fung stresses that nobody knows how long a fast autophagy actually requires, or whether it can be reached on keto alone. For the CrossFit audience, they close on exercise: training in the fasted state, Fung argues, exploits the counter-regulatory hormone surge — catecholamines that sharpen focus (he cites MMA fighter Georges St-Pierre) and a growth-hormone rise that aids recovery — though for elite athletes chasing peak in-season performance, he concedes the calories may be better spent eating, possibly low-carb. As with all clinical claims in these videos, Fung’s reported outcomes are his own clinical experience and published case reports, not the results of controlled trials.
Key points
- Fung says his turning point was clinical: prescribing insulin to type 2 diabetics made them gain the very weight that worsens the disease, while the patients themselves — their willpower, their activity — hadn’t changed.
- He calls the calories model the lowest level of thinking about obesity — like explaining a plane crash as lift losing to gravity — and argues hunger and metabolic rate, the real controls on calories in and out, are hormonally regulated, with insulin foremost.
- His two-sided test: give insulin and people get fat; withhold it, as in untreated type 1 diabetes, and people waste away — which he says identifies insulin as a root cause of fat accumulation.
- Fung recounts a case series he published in BMJ Case Reports: three patients with roughly 20 years of type 2 diabetes each, on 24-hour fasts three times a week, off all insulin within 5 to 18 days and essentially non-diabetic within two months.
- His honest arithmetic: about half of patients won’t attempt fasting, about half of the rest drop out — often after another physician objects — and of those who fast consistently, he estimates roughly 80% improve.
- He says hospital dietitians refused to sign off on the program, and that colleagues were persuaded less by argument than by watching shared patients come off medications.
- Fung and Taubes agree fasting and ketogenic diets pursue the same goal — lower insulin — by different routes; the unresolved scientific question is whether fasting’s suppression of mTOR, and the autophagy it permits, adds something a protein-containing keto diet cannot.
- On training: Fung recommends fasted workouts for recreational athletes for the catecholamine and growth-hormone effects, while conceding elite in-season athletes may need the calories instead.
- The discussion is clinical and anecdotal — Fung’s practice experience and published case reports, not trial evidence — and is presented as such.