Jason Fung

Canadian nephrologist and author whose The Obesity Code challenges the calorie-focused model of weight loss and makes the case for insulin management and intermittent fasting.

Jason Fung is a kidney specialist in Toronto who became interested in obesity and type 2 diabetes through his clinical practice treating patients with kidney disease caused by diabetes. The Obesity Code, published in 2016, argues that the dominant “calories in, calories out” model of weight management is insufficient and that insulin — driven primarily by carbohydrate consumption and eating frequency — is the key regulatory hormone in fat storage. The book draws on epidemiology, physiology, and clinical history to make the case for lower-carbohydrate eating and intermittent fasting as more effective metabolic interventions than calorie restriction alone.

Fung writes clearly and with evident clinical conviction. For readers who have struggled with conventional low-calorie dieting without sustained success, The Obesity Code offers a framework that feels explanatory rather than prescriptive. His dismissal of the diet-food industry and simplistic nutritional advice has the appeal of heterodoxy, and some of his central claims — particularly about insulin’s role in fat accumulation — are supported by substantial metabolic research.

The book also has critics within the medical and nutritional science community who argue that Fung’s synthesis oversimplifies a more complex picture, that his critique of “eat less, move more” is a straw man, and that the evidence base for intermittent fasting as a superior strategy remains mixed. Readers with specific health conditions should consult their physicians before making major dietary changes based on this book. As a challenge to nutritional orthodoxy, The Obesity Code is thought-provoking and worth reading critically.