Peter Attia MD#59–Jason Fung, M.D: Fasting as an antidote to obesity, insulin resistance, T2D, & metabolic illness
CHAPTERS
- 0:04 – 21:00
Physics vs. Medicine: Theory, Evidence, and the Cost of Inaction
Jason Fung argues that medicine could learn from physics, where theories must match experiments and anomalies drive progress. Peter Attia adds that evidence-based medicine works best for acute, simple problems, and both stress the risk of not acting when standard care means slow decline.
- •Fung contrasts physics, where theory yields to experimental anomalies, with medicine's demand for consensus evidence at every step
- •Fung says evidence-based medicine is a search for consensus rather than truth and so moves glacially
- •Attia says the framework suits acute problems like infections but fits chronic disease poorly
- •Both point to the neglected risk of not intervening, such as ever-rising insulin doses and eventual dialysis
- •Fung cites the American Diabetes Association's new low-carb guidance as a reversal from five years earlier
- 21:00 – 29:33
Why Nephrology: The Kidney as an Early Warning System
Fung explains that he chose nephrology because the specialty attracts people who like to think through puzzles. Both discuss why the kidney and eye are early indicators of vascular damage, and Attia describes tracking cystatin C and microalbumin for longevity.
- •Fung says nephrologists are the thinkers of internal medicine, and kidney disease has few treatments beyond prednisone and dialysis
- •Attia describes how the kidney filters everything and pulls back the good, like pulling out all the socks and returning the right ones
- •The kidneys receive about 20% of circulation, and urinary albumin reveals vascular damage elsewhere
- •Attia tracks cystatin C and microalbumin to spot hidden kidney decline decades early
- •Kidney disease is silent, and simple urine testing can catch it
- 29:33 – 42:35
Rethinking Insulin Resistance: The Overflow Paradigm
Fung lays out the conventional lock-and-key view of insulin resistance and the central paradox it creates: the same cell is resistant in one function and hypersensitive in others. He proposes an overflow model, illustrated with a suitcase analogy, where cells are too full of glucose and the real problem is hyperinsulinemia.
- •The standard view treats insulin as a key and the receptor as a lock gummed up, leading to cellular starvation
- •Fung says de novo lipogenesis, growth effects and testosterone effects run high even as glucose uptake is supposedly resistant
- •Attia adds that fat cells keep growing in obesity despite supposed insulin resistance
- •Fung's suitcase analogy distinguishes a closed suitcase from a full one
- •If the cause is overflow, the solution is emptying the cell, not forcing in more insulin
- 42:35 – 53:18
Why Drugs That Add Insulin Fail, and the Case for SGLT2 Inhibitors
Attia asks about the drug classes used in type 2 diabetes, and Fung explains that sulfonylureas, insulin and DPP-4s push more glucose into already full cells. He cites the ACCORD, ADVANCE and VADT trials, then presents SGLT2 inhibitors as the first class that removes glucose from the body and protects organs.
- •Sulfonylureas, insulin and DPP-4s increase insulin, so the disease progresses even when blood sugars improve
- •Fung says ACCORD, ADVANCE and VADT showed no benefit from tight glucose control, which started his rethinking in 2008
- •Attia says lowering glucose with much higher insulin doesn't improve macrovascular outcomes
- •Fung describes the problem as whole-body glucose, not just blood glucose
- •SGLT2 inhibitors make people pee out sugar and show organ protection despite small A1C changes
- 53:18 – 59:06
Metabolic Syndrome as Hyperinsulinemia and the Role of Exercise
Attia raises exercise as another way to empty glucose reservoirs, and Fung says it helps but is less efficient than dietary change. Fung then explains how hyperinsulinemia ties together every component of metabolic syndrome, and Attia compares this with other endocrine diseases.
- •Attia suggests muscle is a large reservoir that exercise can fill; Fung agrees there is a benefit but says it is much less efficient than diet
- •Fung says the liver is key and can't be exercised
- •Hyperinsulinemia links high glucose, triglycerides, low HDL, abdominal obesity and high blood pressure
- •Fung calls it a syndrome of hyperinsulinemia, not insulin resistance
- •Attia notes that endocrinology treats hyper- and hypo- states differently and that excess hormones are harder to treat than deficiencies
- 59:06 – 1:08:33
Biochemical Feedback, Fatty Pancreas, and Reversing Type 2 Diabetes
Fung explains the biochemical negative feedback that blocks glucose entry and says fasting is the most direct way to empty cells. He argues that type 2 diabetes is a single defect, with fatty liver causing hyperinsulinemia and fatty pancreas causing beta cell failure, and cites bariatric surgery and Roy Taylor's work as evidence of reversibility.
- •ATP feedback on glycolysis explains how an overfull cell blocks further glucose
- •Attia says fasting lowers insulin more than carbohydrate or fat restriction
- •Fung says beta cell failure is a clogged, fatty pancreas, not atrophy, which explains why diabetes reverses
- •Bariatric surgery reverses diabetes in most patients, and even a three-year-old developed type 2 diabetes
- •Fructose drives fatty liver through de novo lipogenesis without much glycemic or insulin effect
- 1:08:33 – 1:17:58
Fatty Liver, Causation, and Obesity as a Protective Response
Attia asks whether NAFLD and hyperinsulinemia cause each other, and Fung says the arrow runs both ways in a vicious cycle. Fung argues that obesity, insulin resistance and beta cell failure are protective responses to excess glucose and insulin, citing lipodystrophy.
- •Attia says NAFLD and hyperinsulinemia are tightly linked and resolve together clinically
- •Fung cites fructose-feeding experiments suggesting fatty liver and hyperinsulinemia reinforce each other
- •Fung describes obesity, insulin resistance and glycosuria as protective mechanisms against too much glucose and insulin
- •Lipodystrophy patients with no fat show severe insulin resistance
- •Giving insulin leads to weight gain, and SGLT2 drugs and removing insulin lead to weight loss
- 1:17:58 – 1:28:03
Does Adiposity or Inflammation Drive Hyperinsulinemia? Other Hormones
Attia asks whether adiposity drives hyperinsulinemia, and Fung points to insulin-dosing experiments and liposuction studies to argue causation runs from insulin to obesity. They then discuss inflammation, with Fung finding it too messy to act on, and the roles of cortisol and sex hormones.
- •Fung says a randomized insulin trial produced weight gain despite lower calorie intake
- •Liposuction removing fat didn't change metabolic outcomes, though Attia notes it only removes subcutaneous fat
- •Fung notes that anti-inflammatory drugs don't reliably cause weight loss
- •Attia describes patients with both inflammation and hyperinsulinemia who respond less to carbohydrate restriction
- •Cortisol, sleep and sex hormones also affect body fat, per Fung
- 1:28:03 – 1:36:06
Insulin, Growth Pathways, Cancer and Cardiovascular Disease
Attia asks why hyperinsulinemia worsens vascular disease, and Fung frames cardiovascular disease and cancer as diseases of too much growth tied to insulin, mTOR and AMPK. They discuss rapamycin, how anabolic different hormones are, and the parallel between antibiotic and insulin resistance.
- •Fung treats heart disease and cancer as diseases of excessive growth linked to insulin via PI3K
- •Fung says insulin, mTOR and AMPK are nutrient sensors working on different timescales
- •Attia relays a theoretical 2006 paper predicting rapamycin as a longevity drug, which he finds compelling
- •Attia compares insulin, testosterone and cortisol on muscle and fat
- •Fung compares insulin resistance to antibiotic resistance, both caused by overuse and worsened by more of the same
- 1:36:06 – 1:40:17
Fasting Hits All Three Nutrient Sensors
Fung argues that, unlike a single-target drug such as rapamycin, intermittent fasting lowers insulin, lowers mTOR and raises AMPK together. He ties this to long-standing religious fasting traditions.
- •Insulin responds to carbohydrate and protein, mTOR mostly to protein, and AMPK to cellular energy
- •Rapamycin affects only one of the three sensors
- •Fasting lowers insulin and mTOR and raises AMPK
- •Fung notes it is free and was recommended by religions 2,000 years ago
- 1:40:17 – 1:48:11
Time-Restricted Eating, Diet Restriction, and Why Fung Starts with Fasting
Attia sets out his framework of time-restricted feeding versus dietary restriction. Fung explains he focuses on when to eat because it is easier to explain in a short clinic visit and fits cultural food traditions, and he describes a case series where patients got off insulin quickly.
- •Attia says most diets beat the standard American diet
- •Fung says the idea of eating six to eight times a day has no scientific basis
- •Carbohydrate restriction is hard for patients whose traditional diets center on rice and noodles
- •Fasting is understood across religions and can be explained in ten minutes
- •Three patients with long-standing diabetes got off insulin in 5 to 18 days on 24-hour fasts three times a week
- 1:48:11 – 1:53:14
Fasting as Medical Bariatrics
Attia describes bariatric surgery's quick diabetes resolution and asks how much is due to anatomy, nutrition or caloric restriction. Fung says fasting does everything, citing Roy Taylor's data on liver and pancreatic fat, and calls it medical bariatrics, and they discuss malabsorption and lap bands.
- •Attia describes how Roux-en-Y surgery can end insulin need within days
- •Fung says liver fat and insulin resistance fall right away during fasting, with pancreatic fat and insulin response improving more slowly
- •Fung calls fasting medical bariatrics
- •Attia thinks other mechanisms may contribute; Fung notes malabsorption in Roux-en-Y
- •Fung says purely restrictive lap bands failed because people drank calories
- 1:53:14 – 2:02:59
Cultural Eating Habits, Skipping Breakfast Studies, and 16/8 Time-Restricted Feeding
Fung says people can fast when the culture supports it, while modern habits push constant snacking. They discuss a study linking breakfast skipping to cardiac mortality, calling it confounded, and compare the practicality of eating windows with counting carbs or calories.
- •Fung says people can fast under norms like Ramadan, but modern culture pushes constant snacks
- •Both critique nutritional epidemiology and the breakfast study for confounding and non-healthy user bias
- •Fung says people eat across about 15 hours a day now versus a 14-hour overnight fast in the 1970s
- •Fung finds eating windows far easier to implement than counting carbs
- •Attia has seen mixed results with 16/8 and tightens windows, and defines intermittent fasting more strictly
- 2:02:59 – 2:12:51
Fasting Protocols and a Diabetic Foot Ulcer Case
Attia asks about Fung's protocols, and Fung says he individualizes by severity, age, urgency and willingness. He describes starting a man with a non-healing diabetic foot ulcer on a seven-day fast followed by 36-hour fasts, and the two compare how aggressively they begin.
- •Fung individualizes by severity, age, urgency and patient willingness, from short fasts to a woman who did 61 days
- •The foot ulcer patient started with a week of fasting then 36 hours three times a week, and the ulcer healed in about three weeks
- •Attia usually starts with time restriction and a week of ketosis, while Fung says there's no easy way and warns patients it will be tough
- •Fung describes wading in versus cannonballing into fasting
- •Fung says dogmatism comes from not seeing patients, since individual responses vary
- 2:12:51 – 2:25:09
Patient Willingness, Support, and Practical Tips for Fasting
Fung says about half of patients refuse any fasting and only about 20% accept a longer fast, with psychology being the main barrier. They discuss community support and tips for sleep, electrolytes, hunger and what to expect.
- •Fung says 50% won't fast at all and about 20% might do a longer fast, with psychology the hurdle
- •Support from family and doctors matters, as with Ramadan
- •Fung warns patients beforehand about headaches, cramps and sleep trouble, and Attia suggests phosphatidylserine and GABA for sleep
- •Fung supplements magnesium, uses bone broth if needed, and has never had to stop a fast for electrolytes
- •Attia says even seasoned fasters get hungry, and that anticipation of hunger is harder than the hunger
- 2:25:09 – 2:42:05
Muscle Loss Concerns and Fasting in Healthy People
Fung says protein loss during fasting is limited and may be beneficial in patients with excess body fat, and he has never stopped a patient over muscle loss. Fung also argues that periodic fasting has a very low risk, and they discuss the evidence, Longo's fasting-mimicking diet and gallstones.
- •Fung says he treats older, overweight patients, not bodybuilders, and has had zero patients stopped over muscle loss
- •Fung argues fasting spares skin and connective tissue problems he sees after chronic calorie restriction
- •Fung says periodic fasting lowers insulin and could reduce hyperinsulinemia-related disease in healthy people
- •Fung says five days of fasting a year means missing about 15 of 1,000 meals, so the risk is low
- •Fung blames low-fat diets for gallstones and sees no fasting-related increase
