Dr. Jason Fung, MD

Fung came to insulin through kidney medicine, not weight loss. Treating patients with diabetes and obesity as a nephrologist, he kept seeing insulin, not calorie intake, as the variable that predicted who got sicker and who improved. The Obesity Code turned that clinical observation into a full framework: obesity is a hormonal disorder driven by chronically elevated insulin, and any approach that does not lower insulin is treating the wrong target.

Fasting is the lever Fung uses most, because it is the most direct way to give insulin an extended break. In The Complete Guide to Fasting, he lays out how eating windows of varying length let insulin fall low enough for the body to access stored fat for fuel. RealFoods' fasting tracker follows that same logic, timing eating windows to support the insulin drop Fung's clinical work describes rather than treating fasting as a form of restriction.

The Diabetes Code extends the argument to type 2 diabetes specifically, making the case that reversing insulin resistance matters more than chasing blood glucose numbers alone. That distinction, glucose readings versus the insulin resistance behind them, runs through the WI Score as well. Anyone new to fasting can see how the stages work in practice below.

Fung's nephrology background also shapes how he talks about obesity and metabolic health more broadly. Kidneys are deeply involved in glucose and insulin regulation, and Fung has argued that treating obesity as simple math, what goes in against what goes out, ignores the hormonal signaling his own field of medicine takes for granted. That is part of why his fasting protocols are framed clinically, as a tool for lowering insulin on a schedule, rather than as a lifestyle trend. RealFoods borrows that same clinical framing for its own fasting windows, tracking time rather than restriction. Fung's wider point, that obesity and metabolic health sit downstream of a hormone, not a habit of overeating, is the same starting assumption behind the WI Score, which is why a fasting window and a food's insulin impact are treated in RealFoods as two views of the same underlying signal.