Dr. Jason Fung explains why obesity isn’t caused by calories alone—and how insulin, fasting, and food quality drive weight gain and metabolic disease.

Dr. Jason Fung challenges the long-standing belief that obesity is simply a calorie problem. He explains how hormones—especially insulin—control fat storage, hunger, and energy use, and why highly processed foods disrupt natural satiety signals. The conversation explores fasting as a simple, powerful strategy to lower insulin, improve metabolic health, and address obesity, diabetes, and chronic disease at the root rather than relying on calorie counting alone.

Dr. Fung completed medical school at the University of Toronto and a fellowship in nephrology at UCLA. 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. This observation led him to intermittent fasting–combined with a low-carb, healthy high-fat nutrition plan–– as a way to lower insulin and force the body to burn fat as energy. Today, Dr. Fung has prescribed this treatment to thousands of patients who have seen results that include reversal of type 2 diabetes, weight loss, and 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 numerous other books on disease prevention, including The PCOS Plan, The Cancer Code, and, in 2025, he wrote the follow-up to The Obesity Code, called The Hunger Code.

Dr. Fung continues to practice medicine in Toronto, where he is also the co-founder of The Fasting Method. This program helps patients lose weight and reverse their type 2 diabetes and obesity naturally.