The Obesity Code: Unlocking the Secrets of Weight Loss

FROM NEW YORK TIMES BESTSELLING AUTHOR DR. JASON FUNG—the physician widely credited with popularizing intermittent fasting for weight loss—comes the landmark book that is helping millions around the world achieve natural, sustainable weight loss.

The Obesity Code is a groundbreaking, science-based guide to lasting weight loss that goes beyond “calories in, calories out.” Instead of blaming lack of willpower, practicing physician Dr. Fung explains how hormones—especially insulin—drive weight gain, cravings, and stubborn belly fat. If you’ve tried countless diets and always regain the weight, this book shows you why, and what to do differently.

Drawing on clinical research and real patient success stories, The Obesity Code reveals how insulin resistance and constantly elevated insulin levels lock your body into fat-storage mode. Traditional low‑fat diets, frequent snacking, and severe calorie restriction can actually make things worse, slowing your metabolism and increasing hunger. Dr. Fung shows you how to work with your biology instead of against it, so you can lose weight naturally and improve your metabolic health.

Dr. Fung is often cited as the founder of intermittent fasting for weight loss. Rather than another restrictive fad, intermittent fasting is a flexible, practical tool you can adapt to your lifestyle. You’ll learn:
How intermittent fasting helps lower insulin and unlock stored fat
Different fasting methods (including 16:8, 24‑hour fasts, and more)
How to start safely and manage hunger, social events, and busy days

In addition to when you eat, Dr. Fung explains what to eat for sustainable, natural weight loss. The Obesity Code emphasizes:
Whole, unprocessed foods instead of ultra‑processed snacks
Minimizing sugar and refined carbohydrates that spike insulin
Including healthy fats, quality protein, and fiber‑rich vegetables
A realistic, adaptable approach rather than a rigid, one‑size‑fits‑all diet

Whether your goal is to lose weight, reduce belly fat, reverse pre‑diabetes or type 2 diabetes, or simply improve overall health and wellness, The Obesity Code provides clear explanations and actionable steps. It’s ideal for readers who want to:
Lose weight naturally
Learn how to intermittent fast for weight loss
Reverse insulin resistance
Gain science-backed weight loss information

If you’re tired of yo‑yo dieting, conflicting diet advice, and short‑term fixes, The Obesity Code offers a clear, evidence‑based roadmap to lasting change. Learn how to rebalance your hormones, use intermittent fasting effectively, and finally achieve the healthy, sustainable weight loss you’ve been looking for.

Jason Fung, MD, turned his passion for disease prevention into a groundbreaking, clinically proven, and natural treatment for type 2 diabetes and obesity that has helped thousands of people around the world lose weight and reverse and prevent metabolic disease. Often called the founder of intermittent fasting, Dr. Fung was one of the first medical doctors to prescribe a lowcarb, high healthy fat diet alongside intermittent fasting to his patients struggling with diabetes and obesity. Today, Dr. Fung continues to promote the fasting lifestyle while simultaneously addressing the root causes of hunger and overeating in his patients.

Dr. Fung completed medical school at the University of Toronto and a fellowship in nephrology (kidney medicine) at University of California, Los Angeles before going on to practice nephrology in Toronto. Dr. Fung is also the co-founder of The Fasting Method, a program that helps patients lose weight and reverse their type 2 diabetes naturally.

As a young nephrologist (kidney doctor) working with patients whose type 2 diabetes had led to kidney disease, Dr. Fung saw a clear relationship between prescribed insulin medication and weight gain, an observation that led him to intermittent fasting as a way to lower insulin and force the body to burn fat as energy. Today, Dr. Fung has prescribed intermittent fasting and a low-carb diet to thousands of patients. They have seen results that include reversal of type 2 diabetes, weight loss, and an overall higher quality of life and wellbeing.

In 2016, Dr. Fung published one of the first popular science books to recommend intermittent fasting for weight loss, The Obesity Code, which went on to sell over 2 million copies worldwide. Next he published The Diabetes Code, which lays out his foundational approach to type 2 diabetes prevention and reversal. A New York Times-bestselling author, Dr. Fung has written and contributed to numerous other books on disease prevention, including The PCOS Plan, Life in the Fasting Lane, The Cancer Code, and the follow-up to The Obesity Code, The Hunger Code.

“Fung successfully combines plenty of research, his clinical experience, and sensible nutrition advice, and also addresses the socioeconomic forces conspiring to make us fat.”
—Harvard Health

“Not only full of insights but also surprisingly funny. Read it to understand why the world became fat, how to reverse the epidemic—and how to stay thin yourself.”
—Andreas Eenfeldt, MD, Founder of Dietdoctor.com

“Dr. Jason Fung’s explanation of insulin resistance and the accompanying insulin model of obesity is original, brilliant and game changing.”
—Zoë Harcombe, Obesity researcher, author of The Harcrombe Diet

“A fantastic book that exposes some of the world's most pervasive myths about obesity and weight management. A must read for anyone interested in the science of diet.”
—Kris Gunnars, nutrition researcher

“In The Obesity Code, Dr. Jason Fung triumphs in explaining the core underlying causes of obesity and manages to simplify it in a way that anybody can understand. If more doctors and people were able to understand these causes and implement Dr. Fung's actionable advice then we would be able to start reversing the obesity epidemic tomorrow.”
—Sam Feltham, USA Today World Fitness Elite Trainer of the Year