07/17/2026
Dr. Jason Fung argues that insulin, rather than calories alone, is the primary driver of weight gain. According to his theory, insulin is the body's main fat-storage hormone, and chronically high insulin levels caused by frequent eating, refined carbohydrates, and sugary foods encourage fat storage while reducing the body's ability to burn stored fat. He believes that lowering insulin through approaches such as intermittent fasting and low-carbohydrate diets is a more effective strategy for weight loss than simply counting calories.
Current scientific evidence supports the idea that insulin plays an important role in fat metabolism and that persistently high insulin levels are associated with obesity and metabolic disease. However, most experts do not consider insulin to be the only or primary cause of weight gain. The prevailing view is that body fat increases when energy intake exceeds energy expenditure over time, while hormones such as insulin influence appetite, metabolism, and fat storage. Thus, insulin is regarded as an important factor in weight regulation, working alongside calorie balance, genetics, physical activity, sleep, and other lifestyle factors.