Jason Fung: Books, Clinic and Legacy

Jason Fung, MD, is a Canadian nephrologist — a kidney specialist — in Toronto who has written and lectured since the early 2010s 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.

This page gathers what he has put into the world beyond the hospital: the books he has written or co-written from 2016 to 2026, with their years and co-authors; the fasting program he co-founded with Megan Ramos in 2012; the case reports that program produced; his lectures, video channel and podcast appearances; and the later research on the same subjects — fasting, insulin, weight and type 2 diabetes — described as later research, without verdicts. His ideas themselves are set out in detail on the sibling pages listed under Connections.

Table of Contents

  1. His Books at a Glance
  2. The Obesity Code and How the Books Began
  3. The Fasting Books
  4. The Diabetes Code and The Polycystic Ovary Syndrome Plan
  5. The Longevity Solution and The Cancer Code
  6. The Cookbooks
  7. The Hunger Code in 2026
  8. The Fasting Program He Co-Founded
  9. Case Reports from the Program
  10. Lectures, Video and Podcast
  11. Later Research on the Same Subjects
  12. Key Research Papers
  13. Connections
  14. Featured Videos

1. His Books at a Glance

Between 2016 and 2026 Fung wrote, or co-wrote, the books below. Titles, years and co-authors are taken from library catalogue records; subtitles are given where the records agree on them. The three books that carry the word “Code” and that he wrote alone — on obesity, type 2 diabetes and cancer — are the backbone of his public work, and each has its own page on this site.

Read in order, the list traces a path: first a theory of weight (2016), then the practical tool he built on it, fasting (2016 and 2020), then the same insulin argument carried into type 2 diabetes (2018), polycystic ovary syndrome (2020), ageing (2019) and cancer (2020), and finally, in 2026, back to appetite and the modern food supply.

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2. The Obesity Code and How the Books Began

By Fung’s account, the books grew out of his lectures. Around 2011–2012 he began speaking to colleagues and patients about insulin, low-carbohydrate eating and intermittent fasting, and in about 2014 a publisher approached him after one of those lectures. The result was The Obesity Code, published in 2016.

The book sets out what he calls the hormonal obesity theory. On his own website he summarises it in plain terms: “Raising insulin levels causes weight gain. Lowering insulin levels causes weight loss.” He writes that insulin is “the hormonal signal to the body to increase weight” — a body-set-weight thermostat — and that “The question is NOT how to balance calories, the question is how to balance our hormones.”

He describes two of the 2008 trials that changed his thinking: a two-year New England Journal of Medicine diet trial in which the low-carbohydrate arm lost the most weight, and the ACCORD and ADVANCE trials of intensive glucose lowering in type 2 diabetes, whose results he reads as showing that pushing blood sugar down with more medication did not deliver the expected benefit. Those trials, he says, turned him away from the calorie-balance model.

The full argument, the studies he draws on and the later research on the same question are set out on the sibling page The Obesity Code: Jason Fung’s Hormonal Theory of Obesity.

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3. The Fasting Books

If The Obesity Code is the theory, the fasting books are the practice he builds on it. Fung writes that “Fasting is the most efficient and consistent strategy to decrease insulin levels,” and two of his books are given over to it.

The Complete Guide to Fasting (2016), written with Jimmy Moore, covers the three patterns named in its subtitle — intermittent, alternate-day and extended fasting. It appeared the same year as The Obesity Code and set out in long form the fasting schedules he had been describing in lectures and blog posts.

Life in the Fasting Lane (2020), written with Eve Mayer and Megan Ramos, takes a different angle. As its subtitle says, it is about making intermittent fasting a lifestyle — the day-to-day experience of living with a fasting schedule rather than the physiology behind it.

In his own writing on fasting, Fung also sets limits. He writes that “patients that are severely underweight or malnourished should not fast”, and he describes refeeding syndrome — dangerous shifts in salts such as phosphate, potassium and magnesium when food returns after starvation — as the main hazard for people who are already wasted. His account of the physiology of fasting, and the controlled trials of fasting patterns, are on the sibling page Jason Fung on Intermittent and Therapeutic Fasting.

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4. The Diabetes Code and The Polycystic Ovary Syndrome Plan

The Diabetes Code (2018) applies the insulin argument to type 2 diabetes, the disease Fung saw every day as a nephrologist because it is a leading cause of kidney failure. The book carries a foreword by the journalist Nina Teicholz. In it, and in a long blog series that preceded it, Fung describes type 2 diabetes as a disease of too much insulin and too much stored sugar and fat — an “overflow” — rather than of too little insulin. He writes that “Type 2 Diabetes is a fully reversible condition” and that the defects in insulin resistance and in the insulin-making beta cells are “entirely reversible by removal of the excess fat clogging the organs.”

The book also contains his view of standard drug treatment. He writes that treatments which raise insulin “will not make the disease better. It will only make it worse!” That is his stated position, reported here as his; this site gives no advice on medication. One safety fact applies to anyone on glucose-lowering medicines: changing eating or fasting patterns while taking insulin or drugs that push insulin up can cause low blood sugar, and the case reports in section 9 describe patients whose insulin was stopped while they were followed by the clinic.

The PCOS Plan (2020), written with the naturopathic doctor Nadia Brito Pateguana, carries the same reasoning into polycystic ovary syndrome, a hormonal condition of women that is often accompanied by insulin resistance. Its subtitle frames diet and fasting as the means to “prevent and reverse” the condition — the authors’ framing, as with the diabetes book.

The diabetes argument in full, with the trials it draws on, is on The Diabetes Code: Jason Fung on Type 2 Diabetes.

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5. The Longevity Solution and The Cancer Code

The Longevity Solution (2019) was written with James DiNicolantonio. Its subtitle, “Rediscovering Centuries-Old Secrets to a Healthy, Long Life,” describes its approach: traditional eating and living patterns read through the lens of modern nutrition science, with fasting again among the themes.

The Cancer Code (2020) is the most ambitious of his books and the one furthest from his own specialty. Fung argues that cancer is not mainly a disease of random gene mutations. On his blog he wrote that “Cancer, as a whole, is almost certainly NOT a genetic disease,” and he names the view he puts forward “Cancer Paradigm 3.0”: cancer as an evolutionary process, a “targeted de-evolution to a more primitive form of life”, drawing on the atavistic model of the physicists Paul Davies and Charles Lineweaver and on the old “seed and soil” idea. In his account, high insulin, obesity and processed food make the body’s “soil” fertile for cancer.

The book sets out a theory of how cancer arises; it does not present fasting as a cancer treatment, and neither does this site. The theory and the studies behind it are described on The Cancer Code: Jason Fung’s Evolutionary Theory of Cancer.

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6. The Cookbooks

Two of Fung’s books turn his diet ideas into recipes, each tied by name to one of the “Code” books.

The Obesity Code Cookbook (2019) carries the subtitle “Recipes to Help You Manage Insulin, Lose Weight, and Improve Your Health.” Its premise is the one in The Obesity Code: meals built to keep insulin low rather than to count calories.

The Diabetes Code Cookbook (2021), written with Alison Maclean, describes itself in its subtitle as “Delicious, Healthy, Low-Carb Recipes to Manage Your Insulin and Prevent and Reverse Type 2 Diabetes.” It is the kitchen companion to The Diabetes Code.

Across his writing Fung opposes the low-fat dietary advice of the late twentieth century; on a 2026 video page from the program he co-founded, he is summarised as tracing the obesity and diabetes epidemics to the 1977 dietary guidance to eat more carbohydrate and less fat. That is his reading of the history, reported as his.

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7. The Hunger Code in 2026

Ten years after The Obesity Code, Fung published The Hunger Code in 2026. Bookseller and publisher listings describe it as continuing his “fat thermostat” theme — the idea that the body defends a set weight — and setting it against the rise of ultra-processed food. He discussed the book and his wider ideas on a late-2025 episode of the podcast run by the fasting program he co-founded.

The subject links to one of the best-known recent metabolic-ward studies. In 2019, researchers at the United States National Institutes of Health housed adults on a research ward and offered them, in random order, two weeks of an ultra-processed diet and two weeks of a minimally processed diet, matched for the calories, sugar, fat, fibre and other nutrients on offer, and let them eat as much as they wanted. On the ultra-processed diet the volunteers ate more and gained weight; on the minimally processed diet they ate less and lost weight (Hall 2019). The trial was not designed to test Fung’s insulin theory, but it addresses the same question his new book takes up: why the modern food supply leads people to eat more.

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8. The Fasting Program He Co-Founded

Alongside his hospital work in Scarborough, in 2012 Fung co-founded a fasting program with Megan Ramos. The program describes itself as the first intermittent-fasting clinic in North America; it began as an in-person clinic in Toronto and, from 2014, added online coaching. Fung is listed as its co-founder and chairman and Ramos as its co-founder and chief executive. Ramos is a co-author of several of his papers and of Life in the Fasting Lane.

The program’s own description says the method was developed by Fung and Ramos “after extensive clinical experience.” Patients came to it mainly with obesity and type 2 diabetes, and the clinic combined low-carbohydrate eating with scheduled fasts of varying length. Much of Fung’s blog writing — the long series on hormonal obesity, fasting, type 2 diabetes and cancer that later became his books — was published on the program’s website.

This site describes the program only as part of his biography; it neither reviews nor endorses it.

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9. Case Reports from the Program

Fung and his colleagues published a small set of papers describing patients from the fasting clinic. These are case reports — careful descriptions of individual patients — not controlled trials, and they show what happened to those patients, not what would happen to others.

The authors present the cases as evidence that fasting can be studied as an alternative to insulin; larger controlled trials of intermittent fasting in type 2 diabetes have since been published by other groups (section 11).

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10. Lectures, Video and Podcast

Much of Fung’s reach has come through talks rather than print. He began lecturing on insulin and fasting to colleagues and patients around 2011–2012, and in 2015 he spoke at a low-carbohydrate conference in Cape Town. Lecture recordings and short explanations built a large following online.

His own video channel, “Dr. Jason Fung”, describes itself as offering “Scientific videos on how to lose weight and reverse type 2 diabetes with diets and intermittent fasting.” The program he co-founded runs a separate channel and a podcast, which had reached its 231st episode by November 2025 and regularly features his lectures and conversations. He has also been a guest on other physicians’ podcasts, among them Peter Attia’s, in 2019.

Through these channels the vocabulary of his books — insulin as the “fat-storage” signal, the body-set-weight thermostat, “overflow” in type 2 diabetes — reached many people who never opened one of them. The Featured Videos on this site’s Fung pages are drawn largely from his own channel.

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11. Later Research on the Same Subjects

Fung’s books appeared at a time when fasting, insulin and type 2 diabetes remission were becoming active research fields. The studies below were run by other groups; they are described here as later research on the subjects he wrote about, not as tests of his books.

Together these show the questions his books raised being studied in controlled settings. The detailed trials for each subject are set out on the sibling pages.

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Key Research Papers

  1. 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
  2. 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
  3. 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
  4. 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
  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. de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med. 2019;381(26):2541-2551. — PubMed PMID: 31881139
  7. Cioffi I, Evangelista A, Ponzo V, Ciccone G, Soldati L, Santarpia L, et al. Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: a systematic review and meta-analysis of randomized controlled trials. J Transl Med. 2018;16(1):371. — PubMed PMID: 30583725
  8. Carter S, Clifton PM, Keogh JB. Effect of Intermittent Compared With Continuous Energy Restricted Diet on Glycemic Control in Patients With Type 2 Diabetes: A Randomized Noninferiority Trial. JAMA Netw Open. 2018;1(3):e180756. — PubMed PMID: 30646030
  9. Lean ME, Leslie WS, Barnes AC, Brosnahan N, Thom G, McCombie L, et al. Primary care-led weight management for remission of type 2 diabetes (DiRECT): an open-label, cluster-randomised trial. Lancet. 2018;391(10120):541-551. — PubMed PMID: 29221645
  10. Ludwig DS, Aronne LJ, Astrup A, de Cabo R, Cantley LC, Friedman MI, et al. The carbohydrate-insulin model: a physiological perspective on the obesity pandemic. Am J Clin Nutr. 2021;114(6):1873-1885. — PubMed PMID: 34515299
  11. Hall KD, Ayuketah A, Brychta R, Cai H, Cassimatis T, Chen KY, et al. Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metab. 2019;30(1):67-77.e3. — PubMed PMID: 31105044

PubMed Topic Searches

  1. Intermittent fasting, type 2 diabetes and insulin
  2. Therapeutic fasting case reports
  3. Hyperinsulinemia as a cause of obesity
  4. Type 2 diabetes remission with weight loss

Further Reading

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Connections