Obesity – Dr Jason Fung’s weight loss secret

Image: Foter.com/CC BY-NC

By Marika Sboros

Dr Jason Fung

Dr Jason Fung can make you fat – even obese – or thin. Fung, a Canadian physician and nephrologist (kidney specialist), is the closest modern medicine comes to a “magician”.  

He is busily transforming weight loss and diabetes treatment landscapes in Canada and internationally. He is also disrupting conventional medical and dietetic “wisdom”. His magic is food as medicine. 

Fung’s provocative prescription for weight loss is in his latest book, The Obesity Code, Unlocking The Secrets of Weight Loss (Scribe). It’s a must-read if you want to lose weight and boost your health at the same time.  He also reveals what’s really behind global epidemics of so-called “non-communicable diseases” (NCDs).

NCD is the medical profession’s clumsy term for skyrocketing rates of obesity, diabetes, heart disease, cancer. Dementia is another NCD. Its incidence is rising so rapidly across the planet that doctors are calling it “type 3 diabetes” because of its documented links with diet.

But back to Fung and how he can make you fat or thin. He says that all he has to do is prescribe prednisone – or not.

Stress hormones

Prednisone is a synthetic version of cortisol, the “stress hormone” that occurs naturally in your body as part of a class of steroid hormones known as glucocorticoids. It courses through your bloodstream and gets your heart pounding in so-called “flight or flight” situations.

Doctors prescribe prednisone for conditions such as cancer, asthma, rheumatoid arthritis and inflammatory bowel disease. Fung explains how and why prednisone treats serious disease but also makes you fat. The hormone insulin that your pancreas releases in response to carbohydrate food intake does the same thing.

“It’s not coincidental,” Fung writes, “that both insulin and cortisol play a key role in carbohydrate metabolism.”

Prolonged cortisol stimulation raises glucose levels and subsequently insulin. This increase in insulin plays “a substantial role in the resulting weight gain”.

And there you have it in a nutshell. Your body’s own insulin is the key that unlocks the secret of both weight gain and weight loss. In effect and like so many modern maladies, the key lies in the food you eat. Specifically, food that leads to raised glucose levels and subsequent release of the hormone insulin, he says.

Click here to read: Obesity? Forget fats, it’s the carbs!

In his book, Fung gives an approach to the obesity epidemic that is as controversial as it is scientific. He doesn’t just go against conventional medical and dietetic “wisdom”. He rides roughshod over it and the shaky science on which it is based.

Conventional doctors and dietitians still claim that all you have to do to lose weight is eat less and exercise more. Fung joins a growing chorus of scientific voices who say obesity is not from gluttony and sloth. It doesn’t require pills or potions, starvation diets, hunger, invasive bariatric surgery (cutting away parts of your stomach or intestines). Nor does it even require regular exercise to resolve it.

Fung’s not saying exercise isn’t important. It’s just not a great weight loss tool, for reasons that become crystal clear in his book.

Obesity and hormones

The science is all there to show that obesity really is hormonal and the result of insulin resistance (the inability to tolerate carbohydrate), he says. It just requires willingness to see. 

Fung’s mission in The Obesity Code goes some way to absolving himself of any residual guilt at buying into orthodox medical dogma for so long. He says that he spent more than a decade treating obese and diabetic patients according to conventional medical protocols. Then he realised that, at best, he had helped them to control their symptoms. At worst, he had helped them to stay fat and sick.

Fung set about researching alternatives to conventional medical treatment for obesity and diabetes. He came across good science freely available. It pointed the way to simple, safe steps to achieve significant weight loss quickly and often to reverse all symptoms of type 2 diabetes.

Medicine as art

In his introduction, Fung explains what drove him to make dramatic changes in his treatment methods. He calls it the “peculiar” art of medicine.

 “It allows medical treatments to become established when they don’t really work,” he says. Through “sheer inertia” these treatments “get handed down from one generation of doctors to the next”. The treatments survive for “a surprisingly long time, despite their lack of effectiveness”.

Routine tonsillectomy is just one example. The treatment of obesity is “unfortunately another”, he says.

Click here to read: Think you can outrun bad diet? Fat chance!

 Despite two decades in medicine, Fung acknowledges that his nutrition knowledge was “rudimentary at best”. Like many of his peers, he bought into the CICO (calories-in, calories-out) model of obesity. One issue always worried him. If  CICO were correct, then the medication (insulin) that he prescribed to diabetics should not have caused relentless,  dangerous weight gain.

Fung knew that weight gain was a root cause of type 2 diabetes. He also knew that highly motivated patients who lost significant weight could reverse their diabetes course  completely.

It became clear that calorie reduction for weight loss “has failed miserably”. Yet it remains the treatment of choice, one that nutrition experts continue to defend “vigorously”. 

To stop that conventional juggernaut in its tracks, he set about arming himself with knowledge about the root causes of obesity. One of his biggest weapons – apart from a refreshingly open mind – is science. Don’t expect any animal studies in support of his theories.

Cow parable

Instead, he cites  “The Parable of the Cow”. He also answers a question that has always bothered him: Why are there so many fat doctors?

He explains the parable:

Two cows were discussing the latest nutrition research done on lions. One cow says to the other: “Did you hear that we’ve been wrong for the last 200 years. The latest research shows that eating grass is bad for you and eating meat is good.” So the two cows started eating meat. Shortly thereafter, they both got sick and died.

A year later, two lions were discussing the latest nutrition research done on cows. It showed that eating meat kills you and eating grass doesn’t. The two lions started eating grass and died.

The moral?

“We are not mice, rats, chimps or spider monkeys,” says Fung. “We are humans and should consider only human studies.”

In his book he gives the timeline of the obesity epidemic, its contribution of family history and how both shed light on underlying causes. He demolishes CICO, current dietary guidelines and shortcomings in the current understanding of obesity.

Why so many fat doctors?

Doctors are “accepted authorities in human physiology”. So, they should also be true experts on causes and treatment of obesity. Most doctors are also hardworking and self-disciplined, Fung says. Nobody really wants to be fat. Doctors in particular should have “both the knowledge and dedication to say thin and healthy.

So why are some doctors fat? 

The most likely reason is that they believe and dish out advice to patients that is “simply wrong”, says Fung. A more plausible model is the hormonal theory of obesity. 

Fung explains the central role of insulin in regulating body weight, and the vital role insulin resistance plays. He explores what’s wrong with current diet and dietary guidelines, in particular the role of fat, protein and carbs in weight gain. He offers guidelines for lasting treating of obesity by addressing the hormonal imbalance of high blood insulin.

Fung is also a big fan of intermittent fasting and explains in fascinating detail in this book.

Among its many strengths, this book is reader-friendly, light but always substantial and leavened with humour. Laughter is after all  “best medicine”, and a promoter of understanding and acceptance. Fung makes complex scientific and medical concepts and information accessible to both doctors and lay people.

 Fung’s book  can deservedly be called “original, brilliant and game changing”.  It is primarily about obesity. Ultimately, it’s a gift to both obese and diabetic patients: safe, natural, and speedy reversal of their conditions.



  1. Thanks for a wonderful post. I have a friend who is obese and this has effected her body in every way. She has trouble walking because her knees are so sore which of course is due to her weight. She is also has asthma and is frequently on Prednisone. I will send her your excellent post.

  2. I believe that the first law of thermodynamics is correct BUT only applies in humans when we are metabolically healthy. If you have high insulin levels you are unable to unlock the food you just ate and stored as fat. Instead you feel tired and hungry and gain weight. Your body discourages you from exercise.

  3. Dr. Fung is wrong about animal studies. There are thousands of animal studies that show that the CICO theory is a fraud. Thermodynamic’s laws are the same for all living beings. Those studies can and should be used.

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