Millions struggle with weight loss and type 2 diabetes, often hearing from doctors that their condition is permanent and irreversible.
But Dr. Jason Fung, a New York Times bestselling author and nephrologist, has spent years proving otherwise.
His message is clear: the real problem isn’t calories—it’s insulin.
And understanding this distinction could change everything about how we approach obesity and diabetes.
Type 2 Diabetes Is Reversible—Despite What You’ve Been Told
For decades, the medical establishment taught that type 2 diabetes was a chronic, progressive disease. Once diagnosed, patients were told they’d have it for life.
“During training, all through medical school, doctors basically get told over and over again that it’s a chronic and progressive disease,” Dr. Fung explains. “Once you have it, you have it for life. You’ll never get rid of it and there’s nothing you can do but take your medications.”
Yet the evidence always suggested otherwise.
People who lost weight consistently saw their diabetes improve or disappear entirely. It wasn’t until 2023 that the American Diabetes Association finally added criteria for remission to their guidelines—admitting what patients had known all along.
It was so obvious that it was so untrue that they finally put in criteria for remission in 2023. From the 1960s until 2023, the American Diabetes Association put on its website that this is a chronic and progressive disease. And then finally in 2023, only like 3 years ago, they finally admitted, ‘Oh, hey, actually it can go in reverse.’
The issue was never that reversal was impossible. The issue was that doctors were using drugs to treat a dietary disease.
Why the Calorie Model Fails
Most weight loss advice boils down to one equation: calories in minus calories out equals body fat.
It sounds logical. Eat less, move more, lose weight.
But Dr. Fung argues this model misses the most important part of the equation: hormones.
“For every calorie you eat, your body can either store it or it can burn it,” he says. “Which one does it do? It doesn’t depend on the number of calories. It depends on the hormones that tell your body whether to store it or to burn it.”
When you eat two cookies, insulin spikes. That insulin tells your body to store those calories as fat. Meanwhile, the rest of your body—your heart, lungs, liver—doesn’t get the energy it needs.
So what happens? You stay hungry. You eat more cookies. The cycle continues.
Now imagine eating four eggs instead. Protein and fat don’t spike insulin the same way. Your body burns the energy rather than storing it, and you feel satisfied.
Why do we pretend that 500 calories of cookies are the same as 500 calories of broccoli? They’re completely different.
The hormonal response determines whether you store fat or burn it. That’s why counting calories alone has never worked.
The Real Culprit: Too Much Insulin
Dr. Fung believes the root cause of both obesity and type 2 diabetes is hyperinsulinemia—chronically elevated insulin levels.
Insulin is a natural hormone, but too much of it causes problems. When insulin is high, your body stores fat. When it’s low, your body burns fat.
Starting in the 1970s, dietary guidelines encouraged Americans to eat more carbohydrates and less fat. The result? Insulin levels skyrocketed.
“When you’re eating a lot of carbohydrates, your insulin is going to go way up,” Dr. Fung explains. “And that’s why if you’re spiking insulin, you’re basically telling your body to please store more fat.”
This dietary shift didn’t just make people gain weight. It also increased rates of type 2 diabetes, heart disease, and metabolic syndrome.
