Jason Fung: Life and Career

Jason Fung, MD, is a Canadian nephrologist — a kidney specialist — in Toronto who, since the early 2010s, has written and lectured that obesity and type 2 diabetes are disorders of too much insulin (hyperinsulinemia) rather than of calorie balance, and that fasting is the most direct way to bring insulin down. He is the author of The Obesity Code (2016), The Diabetes Code (2018) and The Cancer Code (2020).

This page follows his working life in plain language: a Toronto upbringing, a medical degree at the University of Toronto, nephrology training at the University of California, Los Angeles (UCLA), more than two decades of kidney medicine in Scarborough, the clinic research on chronic kidney disease that carries his name, the three large 2008 trials he describes as turning points in his thinking, the fasting clinic he co-founded in 2012, the case reports it produced, and the books that brought his ideas to a wide public. His ideas themselves are set out on the sibling pages listed under Connections.

Table of Contents

  1. Toronto, Biochemistry and Medical School
  2. Choosing Nephrology and the UCLA Fellowship
  3. Kidney Medicine in Scarborough from 2001
  4. His Clinic Research on Chronic Kidney Disease
  5. Seven Years of Conventional Practice
  6. The 2008 Trials He Names as Turning Points
  7. Lectures, Low-Carbohydrate Eating and the 2012 Fasting Clinic
  8. Case Reports from the Fasting Clinic
  9. Books, Talks and a Wider Audience
  10. Timeline
  11. Key Research Papers
  12. Connections
  13. Featured Videos

1. Toronto, Biochemistry and Medical School

Jason Fung was born and raised in Toronto, Ontario. He has described an early pull toward engineering before he settled on medicine: he completed two years of biochemistry at university and then went on to a medical degree at the University of Toronto. The year he graduated in medicine is not given in the sources this page draws on, and his date of birth is not set out here; a 2018 profile gave his age as 44, which places his birth in the early 1970s.

The engineering streak matters to the rest of the story. Throughout his later writing Fung frames the body as a system of feedback loops and set points — a thermostat for body weight, an “overflow” of a full container for type 2 diabetes — and he has said plainly that he enjoys medicine most where it behaves like mathematics. That taste shaped the specialty he chose next.

His training in biochemistry also shows in the way his later books are built. The Obesity Code and The Diabetes Code each spend long chapters on hormones, enzymes and the order in which the body uses its fuel stores, before they reach any practical discussion. Fung writes for a general reader, but the scaffolding of each book is physiological rather than dietary: he sets out what he believes insulin does, and the diet chapters follow from that.

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2. Choosing Nephrology and the UCLA Fellowship

After medical school and internal-medicine residency, Fung chose nephrology, the branch of internal medicine that deals with the kidneys, their filtering of the blood, and the balance of salt, water, acid and minerals they maintain. In a 2018 profile he explained the choice in terms of numbers: “In nephrology, you deal with more equations than in other types of medicine and I really like that.”

Kidney medicine is indeed arithmetic-heavy. A nephrologist estimates how well the kidneys filter from a blood test and a formula (the estimated glomerular filtration rate, eGFR), calculates fluid and electrolyte shifts, and doses medicines according to how much kidney function remains. Many of the patients a nephrologist sees have kidneys damaged by diabetes and high blood pressure, so the specialty also puts its doctors face to face, every day, with the late consequences of type 2 diabetes.

He trained in nephrology as a fellow at the University of California, Los Angeles (UCLA) from 1999 to 2001. A fellowship is the subspecialty training a doctor takes after residency; at its end Fung was a qualified kidney specialist.

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3. Kidney Medicine in Scarborough from 2001

In 2001 Fung returned to Toronto to practise nephrology. The author affiliations on his published papers trace where that work was done. Papers from 2006 to 2012 list him in the Department of Nephrology or Renal Division of Scarborough General Hospital, in the eastern part of Toronto. A 2018 paper gives his affiliation as the Department of Medicine, Scarborough Hospital, together with the Corporate Medical Centre in Scarborough; a 2020 paper gives the Department of Medicine of the Scarborough Health Network, the hospital group that Scarborough General became part of.

That is a working span of nearly two decades in one community hospital system, documented in the medical literature itself, and it overlaps fully with the years in which he built his public work on fasting. His best-known argument — that type 2 diabetes is a reversible disease of excess insulin — comes from a specialist whose field treats one of the late complications of diabetes, kidney failure.

His active working span, counted from his first year of practice, runs from 2001 to the present: he is still listed with the Scarborough Health Network on a 2020 paper and was still publishing books, podcasts and videos in 2025 and 2026.

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4. His Clinic Research on Chronic Kidney Disease

Before he was known for fasting, Fung was a co-author on several studies from the Scarborough nephrology division. They are ordinary clinic research — reviews of the division’s own patient records — and they show the day-to-day kidney medicine behind his later public work.

None of these papers concerns fasting or diet. They are listed here because they are part of the documented record of his career as a kidney specialist, and because they show the clinic population — many people with diabetes-related kidney damage — that he describes as the starting point of his interest in reversing type 2 diabetes.

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5. Seven Years of Conventional Practice

Fung has described his first seven or so years of practice as entirely conventional. By his own account he followed the standard advice of the time: low-fat diets for weight control, and strict blood-sugar control, with medicines and insulin, for patients with type 2 diabetes.

In his telling, what changed was not one patient but a run of evidence that did not fit the model he had been taught. That evidence arrived, he says, in 2008.

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6. The 2008 Trials He Names as Turning Points

Fung names three trials, all published in the New England Journal of Medicine in 2008, as the moments that made him question the advice he had been giving. He says these results changed his thinking and led him to reject the calorie (energy-balance) theory of obesity. What follows describes what each trial reported in its abstract.

The two-year diet trial

Shai and colleagues randomly assigned 322 moderately obese adults (mean age 52, most of them men) to a low-fat diet with calorie restriction, a Mediterranean diet with calorie restriction, or a low-carbohydrate diet without calorie restriction, and followed them for two years. Mean weight loss was 2.9 kilograms on the low-fat diet, 4.4 kilograms on the Mediterranean diet and 4.7 kilograms on the low-carbohydrate diet. Fung points to this trial as the one in which the low-carbohydrate diet did best for weight loss, even though it was the one diet whose participants were not asked to restrict calories.

ACCORD: intensive glucose lowering

The Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial assigned 10,251 people with type 2 diabetes and a median glycated hemoglobin (hemoglobin A1c, HbA1c) of 8.1% either to intensive therapy aimed at a hemoglobin A1c below 6.0% or to standard therapy aimed at 7.0–7.9%. The two groups reached median hemoglobin A1c levels of 6.4% and 7.5%. The intensive arm was stopped early, after a mean of 3.5 years, because more people had died in it: 257 deaths against 203 in the standard arm. Intensive lowering did not significantly reduce major cardiovascular events.

ADVANCE: intensive glucose control and vascular outcomes

The ADVANCE trial randomised 11,140 people with type 2 diabetes to intensive or standard glucose control, with a median follow-up of five years. Mean hemoglobin A1c was 6.5% in the intensive group and 7.3% in the standard group. Intensive control reduced the combined rate of major large-vessel and small-vessel events (18.1% against 20.0%), mainly because of fewer cases of new or worsening kidney disease (nephropathy: 4.1% against 5.2%); it had no significant effect on major large-vessel events such as heart attack and stroke, or on death.

What he drew from them

Fung has said that, taken together, these trials showed him two things: that a diet that lowers insulin could outperform calorie counting for weight, and that pushing blood sugar down harder with medicines and insulin did not deliver the protection from heart attacks and strokes that he had expected. From there he came to his central idea — that the problem in type 2 diabetes is too much insulin, and that adding more insulin treats the number rather than the disease. The full argument is on the Diabetes Code and Obesity Code pages.

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7. Lectures, Low-Carbohydrate Eating and the 2012 Fasting Clinic

Around 2011 and 2012 Fung began lecturing, first to colleagues and then to patients, on obesity as a hormonal problem. He then began treating his own patients with low-carbohydrate eating and intermittent fasting — planned periods without food, from a day or so up to several days.

In 2012, together with Megan Ramos, he set up a fasting clinic in Toronto. The program describes itself as the first intermittent-fasting clinic in North America. It added online coaching in 2014, which took the clinic’s approach to people far outside Toronto. Fung is listed as the program’s co-founder and chairman, and Ramos as its co-founder and chief executive.

The clinic is where the fasting schedules described in his books were worked out with real patients, and it is the setting of the case reports in the next section. In his writing he states plainly that people who are severely underweight or malnourished should not fast, because of the risk of refeeding syndrome — a dangerous shift of salts and fluids when food is restarted after starvation. That and the rest of his account of fasting are set out on the Therapeutic Fasting page.

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8. Case Reports from the Fasting Clinic

Alongside his books, Fung and the clinic team published case reports of patients with type 2 diabetes treated with fasting. A case report describes what happened to a small number of individual patients; it is not a controlled trial, and it does not show how often the same result would occur in others.

These reports describe individual patients followed by the clinic team. What Fung argues they show about type 2 diabetes is set out on the Diabetes Code page.

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9. Books, Talks and a Wider Audience

Fung has said that a publisher approached him after one of his lectures, around 2014, and that this led to his first book, The Obesity Code: Unlocking the Secrets of Weight Loss, published in 2016. The same year he published The Complete Guide to Fasting, written with Jimmy Moore. In 2015 he spoke at a low-carbohydrate conference in Cape Town, South Africa.

The books that followed track the themes of his blog series and his clinic. The Diabetes Code: Prevent and Reverse Type 2 Diabetes Naturally appeared in 2018, with a foreword by Nina Teicholz. The Longevity Solution, written with James DiNicolantonio, followed in 2019; Life in the Fasting Lane, with Eve Mayer and Megan Ramos, and The PCOS Plan, with Nadia Brito Pateguana, in 2020; and The Cancer Code: A Revolutionary New Understanding of a Medical Mystery later in 2020. Cookbooks accompanied The Obesity Code (2019) and The Diabetes Code (2021, with Alison Maclean). In 2026 he published The Hunger Code, which carries his “fat thermostat” idea into the subject of ultra-processed food.

He also reaches readers through a YouTube channel under his own name, which describes itself as offering scientific videos on losing weight and reversing type 2 diabetes with diet and intermittent fasting, and through the podcast and videos of the fasting program he co-founded, which had reached its 231st episode by November 2025. In June 2019 he was a guest on episode 59 of fellow physician Peter Attia’s podcast. The full book list, with co-authors and publishers, is on the Books and Legacy page.

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10. Timeline

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Key Research Papers

  1. Sikaneta T, Cheung KM, Abdolell M, Tam P, Ting R, Fung J, et al. The Toronto Western Hospital catheter: one center’s experience and review of the literature. Int J Artif Organs. 2006;29(1):59-63. — PubMed PMID: 16485240
  2. Taskapan H, Tam P, Au V, Chow S, Fung J, Nagai G, et al. Improvement in eGFR in patients with chronic kidney disease attending a nephrology clinic. Int Urol Nephrol. 2008;40(3):841-8. — PubMed PMID: 18386153
  3. Taskapan H, Tam P, Leblanc D, Ting RH, Nagai GR, Chow SS, et al. Peritoneal dialysis in the nursing home. Int Urol Nephrol. 2010;42(2):545-51. — PubMed PMID: 20174996
  4. Sikaneta T, Abdolell M, Taskapan H, Roscoe J, Fung J, Nagai G, et al. Variability in CKD stage in outpatients followed in two large renal clinics. Int Urol Nephrol. 2012;44(5):1461-6. — PubMed PMID: 21424573
  5. Shai I, Schwarzfuchs D, Henkin Y, Shahar DR, Witkow S, Greenberg I, et al. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. N Engl J Med. 2008;359(3):229-41. — PubMed PMID: 18635428
  6. Action to Control Cardiovascular Risk in Diabetes Study Group, Gerstein HC, Miller ME, Byington RP, Goff DC Jr, Bigger JT, et al. Effects of intensive glucose lowering in type 2 diabetes. N Engl J Med. 2008;358(24):2545-59. — PubMed PMID: 18539917
  7. ADVANCE Collaborative Group, Patel A, MacMahon S, Chalmers J, Neal B, Billot L, et al. Intensive blood glucose control and vascular outcomes in patients with type 2 diabetes. N Engl J Med. 2008;358(24):2560-72. — PubMed PMID: 18539916
  8. Fung J, Berger A. Hyperinsulinemia and Insulin Resistance: Scope of the Problem. Journal of Metabolic Health. 2016;1(1). — DOI: 10.4102/jir.v1i1.18
  9. Ku M, Ramos M, Fung J. Therapeutic fasting as a potential effective treatment for type 2 diabetes: A 4-month case study. Journal of Metabolic Health. 2017. — DOI: 10.4102/jir.v2i1.31
  10. Furmli S, Elmasry R, Ramos M, Fung J. Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin. BMJ Case Rep. 2018;2018:bcr2017221854. — PubMed PMID: 30301822
  11. Lichtash C, Fung J, Ostoich KC, Ramos M. Therapeutic use of intermittent fasting and ketogenic diet as an alternative treatment for type 2 diabetes in a normal weight woman: a 14-month case study. BMJ Case Rep. 2020;13(7):e234223. — PubMed PMID: 32641437

PubMed Topic Searches

  1. Fung J and Scarborough (his hospital papers)
  2. Intermittent fasting, type 2 diabetes and insulin
  3. Intensive glucose lowering and cardiovascular outcomes
  4. Chronic kidney disease, nephrology referral and eGFR

Further Reading

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Connections