For readers who feel that conventional 'eat less, move more' advice has failed them, The Obesity Code offers a genuinely coherent and accessible alternative framework. The book's dual appeal — rigorous enough for medically informed readers, clear enough for a general audience — helps explain how it made Fung a New York Times bestselling author. The important caveat, flagged by Red Pen Reviews, is that the insulin-as-primary-cause hypothesis is a minority position in the research community, so readers should approach the book as a compelling argument for one contested school of thought rather than as settled science.

Jason Fung

Reviewed

February 17, 2026

Read Time

7 min read

Age & reading levelAdult

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4.6 · 37,979 Amazon ratings

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The Obesity Code

The Obesity Code by Jason Fung Review: A Provocative Hormonal Case for Weight Loss

by Jason Fung

Published by Greystone Books in 2016, The Obesity Code by Dr. Jason Fung — a practicing physician and New York Times bestselling author — argues that obesity is fundamentally a hormonal disorder driven by persistently high insulin levels and insulin resistance, not a simple failure of willpower or calorie counting. The book has become a landmark title in popular nutrition science, and its foreword is written by Timothy Noakes.

$11.00 on Amazon

Adult

LuvemBooks Verdict

Best for

Readers who feel that conventional "eat less, move more" advice has failed them and are encountering the hormonal/insulin framework for obesity for the first time.

Worth it if

Worth reading if you want a coherent, well-sourced, and accessible introduction to the insulin hypothesis and intermittent fasting as a practical strategy — written by a practicing physician and structured across six organised parts with bibliographical references.

Skip if

Skip it if you want a balanced survey of competing obesity research, or if you need the book's central insulin hypothesis to represent settled scientific consensus rather than a forcefully argued, actively contested minority position.

What readers & critics say

Diagnosisdiet.com praises Fung's writing style for striking the right balance — providing enough research to convince even sceptical physicians without overwhelming a general audience. Red Pen Reviews, however, gives the book a modest scientific accuracy score, finding that its three core claims are poorly supported or exaggerated, and that the insulin-as-primary-cause hypothesis remains a minority view difficult to reconcile with the broader body of evidence.

Sources: diagnosisdiet.com, redpenreviews.org

4.6from 37,979 Amazon ratings— reader ratings, not a LuvemBooks score

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The Obesity Code: Unlocking the Secrets of Weight Loss by Dr. Jason Fung argues that obesity is a hormonal disorder driven by chronically elevated insulin levels — not a failure of willpower or calorie counting — and presents intermittent fasting as the central practical solution. Bridging genuine medical depth with broad readability, the book offers a coherent, well-structured challenge to mainstream dietary orthodoxy and is best suited to readers who feel conventional diet advice has failed them. The key caveat: the insulin-as-primary-cause hypothesis is a minority position in the research community and remains actively contested, so readers seeking settled scientific consensus will need to supplement their reading elsewhere.

Is it worth reading?: For readers who feel that conventional 'eat less, move more' advice has failed them, The Obesity Code offers a genuinely coherent and accessible alternative framework. The book's dual appeal — rigorous enough for medically informed readers, clear enough for a general audience — helps explain how it made Fung a New York Times bestselling author. The important caveat, flagged by Red Pen Reviews, is that the insulin-as-primary-cause hypothesis is a minority position in the research community, so readers should approach the book as a compelling argument for one contested school of thought rather than as settled science.
Similar books: Readers drawn to The Obesity Code will find natural follow-on reading in several related titles. Dr. Fung's own The Complete Guide to Fasting (co-authored with Jimmy Moore) extends the intermittent fasting argument into a practical manual. Casey Means and Calley Means's Good Energy similarly centers metabolic health as the key to overall wellbeing. Peter Attia's Outlive: The Science and Art of Longevity offers a rigorous, physician-authored look at the science of living longer that overlaps on nutrition and metabolism. For those interested in the food system that shapes our diets, Michael Moss's Salt Sugar Fat and Michael Pollan's In Defense of Food provide essential context, while Michael Greger's How Not to Diet offers a data-driven counterpoint on the science of weight loss.
Who should read this?: The Obesity Code is most likely to resonate with readers who feel conventional diet advice — eat less, move more, count calories — has repeatedly failed them and who are open to a hormonal explanation for why that might be. It also appeals to medically curious readers who want a physician-authored, research-referenced challenge to mainstream nutritional orthodoxy, as well as anyone seeking a rigorous yet accessible introduction to intermittent fasting. Those who want a balanced survey of competing obesity research, or who expect the insulin hypothesis to represent scientific consensus, should approach with that expectation adjusted.
About Jason Fung: Peter Daou is a Lebanese-American political activist, musician, and author.
How does this compare to The Complete Guide to Fasting?: The Obesity Code and The Complete Guide to Fasting (co-authored with Jimmy Moore) are complementary works that serve different purposes. The Obesity Code builds the theoretical and scientific foundation — arguing that obesity is a hormonal disorder and that insulin is the primary driver — while The Complete Guide to Fasting focuses on practical application, detailing specific fasting protocols and implementation strategies. Readers new to Fung's framework are best served starting with The Obesity Code before moving to the fasting guide.
What is Fung's core argument?: Fung's central thesis is that obesity is not caused by excess calorie intake or lack of willpower, but is a hormonal disorder driven by chronically elevated insulin levels and insulin resistance. A diet high in carbohydrates and high eating frequency, the theory holds, keeps insulin persistently elevated, which promotes fat storage and prevents the body from accessing stored energy for fuel. The practical implication is that breaking the cycle requires reducing carbohydrate intake and lowering eating frequency — with intermittent fasting as the primary recommended tool. This framework is similar to the carbohydrate-insulin model proposed by obesity researcher David Ludwig, MD, PhD, though it remains actively debated rather than settled science.

Summarize this book

Is it worth reading?

Who should read this?

About Jason Fung

How does this compare to The Complete Guide to Fasting?

What is Fung's core argument?

Summarize this book

The Obesity Code, published by Greystone Books in 2016, contends that obesity is fundamentally a hormonal disorder caused by persistently high insulin levels and insulin resistance — not by a lack of willpower or excess caloric intake. Dr. Jason Fung, a practicing physician trained at the University of Toronto and the University of California, argues that a diet high in carbohydrates combined with high eating frequency chronically elevates insulin, promoting fat storage and blocking access to stored energy. The book is organized into six parts, moving from a critique of prevailing obesity 'myths' through a hormonal model of weight gain and on to practical guidance, with intermittent fasting as the recommended therapeutic strategy. It includes bibliographical references and an index, and carries a foreword by sports science figure Timothy Noakes.

The Obesity Code: Unlocking the Secrets of Weight Loss by Jason Fung

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A landmark work in popular nutrition science, The Obesity Code makes the case that the conventional understanding of obesity has been wrong all along — and proposes a hormonal framework to replace it.

What the Book Actually Argues

At its core, The Obesity Code contends that obesity is a hormonal disorder of persistently high insulin levels and insulin resistance, caused by eating the wrong foods too often — not by a lack of willpower or an excess of calories and fat grams. Dr. Fung, a practicing physician who completed medical school at the University of Toronto and a nephrology fellowship at the University of California, positions insulin — not caloric intake alone — as the primary driver of weight gain.

A diet high in carbohydrates and high eating frequency, the theory holds, produces chronically elevated insulin, which in turn promotes fat storage and prevents the body from accessing stored energy. Intermittent fasting is presented as the central practical tool for breaking that cycle, a point the book's subtitle — Unlocking the Secrets of Weight Loss (Why Intermittent Fasting Is the Key to Controlling Your Weight) — makes explicit.

Structure and Scope

The book is organized into six parts. The first two examine how obesity became an epidemic and challenge what Fung calls the prevailing "myths" about its causes.

Parts three and four lay out what the book frames as a new model of how obesity develops, along with an examination of sociological contributors to the condition. The final sections move from theory to application.

The volume includes bibliographical references and an index, giving the argument a documented, research-oriented foundation rather than a purely anecdotal one. Timothy Noakes, a prominent figure in sports science and low-carbohydrate nutrition, contributes the foreword — a signal of the intellectual circle in which the book positions itself.

Accessibility and Rhetorical Reach

One of the book's most noted qualities is the way it bridges scientific depth and general readability. As diagnosisdiet.com describes it, Fung's writing style strikes the right balance, providing enough research to convince even skeptical physicians of his argument without overwhelming or boring a general audience.

The cover's own description calls the book "highly readable and provocative." This dual appeal — rigorous enough for medically informed readers, clear enough for anyone frustrated by conventional diet advice — helps explain how it has reached the wide audience that has made Fung a New York Times bestselling author.

Readers come away with a framework for understanding how food affects hormonal networks, a lens the book argues has implications regardless of how much a person weighs.

Where the Book Faces Scrutiny

The Obesity Code has also drawn substantive criticism from within the research community. Red Pen Reviews, which evaluates popular nutrition books against the scientific literature, notes that while some researchers do consider insulin a primary cause of obesity, it remains a minority view that is difficult to reconcile with the body of evidence as a whole.

The review concludes that the insulin hypothesis, as presented, is not established firmly enough to support the strength of the claims Fung makes. The book's model of obesity is similar to the carbohydrate-insulin model proposed by obesity researcher David Ludwig, MD, PhD — a framework that remains actively debated rather than settled science.

Readers who approach the book expecting a consensus scientific position will find instead a forceful argument for one contested school of thought.

Who This Book Is For

The Obesity Code is most likely to resonate with readers who feel that conventional diet advice — eat less, move more, count calories — has failed them, and who are open to a hormonal explanation for why that might be the case. It functions as both an intellectual challenge to mainstream nutritional orthodoxy and a practical introduction to intermittent fasting as a therapeutic strategy.

Those seeking a survey of competing obesity research, or who want to weigh the insulin hypothesis against alternative models in depth, will need to supplement their reading elsewhere. For readers encountering the hormonal framework for the first time, however, the book offers a coherent, well-sourced, and accessible entry point — one that has clearly resonated at considerable scale since its 2016 publication by Greystone Books.

Sources & Further Reading

The key facts and claims in this review are grounded in the retrieved, verified sources listed below.

Cited in this review
1
The Obesity Code: Unlocking the Secrets of Weight Loss (Why Intermittent Fasting Is the Key to Controlling Your Weight)
everand.com
2
The obesity code : unlocking the secrets of weight loss : Fung, Jason, author : Free Download, Borrow, and Streaming : Internet Archive
archive.org
3
The Obesity Code: Unlocking the Secrets of Weight Loss – Red Pen Reviews
redpenreviews.org
Further reading
4
The Obesity Code by Jason Fung MD: Book Review - Diagnosis Diet
diagnosisdiet.com
5
12min - The Obesity Code - Critical summary review - Jason Fung
12min.com
6
The Obesity Code: Unlocking the Secrets of Weight Loss' by Dr. Jason Fung Book Review | BookClub
vocal.media
7
The Obesity Code – Greystone Books Ltd.
greystonebooks.com
8
The Obesity Code: Unlocking the Secrets of Weight Loss (Why Intermittent Fasting Is the Key to Controlling Your Weight) by Dr. Jason Fung, Paperback |
barnesandnoble.com

Age & Reading Level

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Skip if you want a balanced survey of competing obesity research or expect the insulin hypothesis to represent scientific consensus.

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In our catalogue

The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting

Dr. Jason Fung, Jimmy Moore

Fung's practical follow-up: moves from the hormonal theory to step-by-step fasting protocols, meal plans, and troubleshooting for real-world implementation.

Where The Obesity Code makes the scientific case for fasting, this book hands you the operational toolkit — specific fasting schedules, what to eat in eating windows, and how to handle common obstacles like hunger and social pressure. It's co-written with Jimmy Moore, whose patient perspective keeps the tone accessible rather than clinical. Readers who finished Fung's argument and immediately asked "but how do I actually do this?" will find this a natural next step.

If you liked The Obesity Code

In our catalogue

Outlive: The Science and Art of Longevity

Peter Attia

Another physician-author challenging mainstream medicine's chronic-disease assumptions — with metabolic health, insulin resistance, and lifespan as shared obsessions.

In our catalogue

Good Energy: The Surprising Connection Between Metabolism and Limitless Health

Casey Means, Calley Means

Shares Fung's core argument — modern metabolic dysfunction is systemic, not personal — and adds continuous glucose monitoring as a practical self-tracking lens.

In our catalogue

Salt Sugar Fat: How the Food Giants Hooked Us

Michael Moss

Investigative complement to Fung's argument: shows the industry machinery behind the ultra-processed food environment that drives overconsumption and insulin spikes.

In our catalogue

How Not to Diet: The Groundbreaking Science of Healthy, Permanent Weight Loss

Michael Greger

A rigorous, evidence-first weight-loss book that reaches very different dietary conclusions — useful for readers who want to stress-test Fung's insulin hypothesis against competing science.

Not your thing?

In our catalogue

In Defense of Food: An Eater's Manifesto

Michael Pollan

If Fung's clinical depth felt like too much: Pollan makes the same "mainstream nutrition advice is broken" case in a lighter, more literary register with no protocols required.