Obesity models still clashing

A new YouTube video is pushing back on Jason Fung’s insulin-first explanation of obesity, reopening a long-running fight over what makes people gain weight. (youtube.com) The video, titled “Doctor Jason Fung Still Doesn’t Understand Obesity,” was live on YouTube by April 18, 2026, and argues that Fung’s line — “you overeat because you’re fat” — repackages an older carbohydrate-insulin theory. Jason Fung’s YouTube channel lists 1.41 million subscribers, and his website still promotes *The Obesity Code* as a guide built around “fasting, hormones, and insulin resistance.” (youtube.com 1) (youtube.com 2) (doctorjasonfung.com) Fung’s published pitch has been consistent for years: his book description says weight gain is driven by hormones and that lasting weight loss depends on understanding insulin and insulin resistance. His site frames obesity treatment around lowering insulin through diet and fasting rather than treating calories as the main problem. (books.google.com) (doctorjasonfung.com) Mainstream obesity statements describe a broader system. The Endocrine Society says obesity involves appetite regulation and points readers to scientific statements on genetics, development, environment, and behavior, not insulin alone. (endocrine.org) (pmc.ncbi.nlm.nih.gov) That split maps onto a formal research debate. A 2022 review comparing the energy balance model and the carbohydrate-insulin model said both frameworks include genetics, behavior, and environment, but they disagree on what starts the process: overeating in one model, altered fuel partitioning after high-glycemic diets in the other. (pmc.ncbi.nlm.nih.gov) A 2024 *Nature Metabolism* perspective said researchers still lack a single causal model that explains the modern rise in obesity across populations. The paper came out of a Copenhagen workshop that tried to define where the rival models overlap and where they diverge. (nature.com) The appetite-centered side of the argument focuses on the body’s hunger controls and the places people eat. Reviews cited by endocrine and nutrition journals describe appetite as shaped by brain and gut signals, genetics, social context, and the food environment, including the availability of energy-dense processed food. (sciencedirect.com) (nutrition.bmj.com) The insulin-centered side says those same foods matter for a different reason. In that model, refined carbohydrates raise insulin, push more incoming energy into fat storage, and can leave less fuel available to other tissues, which then drives hunger and lower energy expenditure. (pmc.ncbi.nlm.nih.gov 1) (pmc.ncbi.nlm.nih.gov 2) Neither side is arguing over a small problem. The World Health Organization said in its December 8, 2025 fact sheet that 890 million adults were living with obesity in 2022, and adult obesity worldwide has more than doubled since 1990. (who.int) So the latest clash is less about one YouTube upload than about who gets to explain obesity in public: fasting advocates, academic obesity researchers, or creators translating papers for mass audiences. Six years after major journals were still publishing side-by-side model debates, the argument is now playing out in subscriber counts, podcasts, and reaction videos as much as in clinics and journals. (pmc.ncbi.nlm.nih.gov) (nature.com) (youtube.com)