The Obesity Code: what is it and who’s it for?

last updated: Nov 04, 2021

5 min read

As you’re reading this, people worldwide are fighting the obesity epidemic, attempting to lose weight and improve their health. They usually try to accomplish this by: 

  • Counting calories

  • Exercising

  • Saying no to the foods they want to eat

But statistics say that most people won’t succeed or, if they do, they’ll eventually regain the pounds they’ve lost (yo-yo dieting).

Dr. Jason Fung, a Canadian kidney specialist, says that he’s found a solution backed by medical research. He published his findings in his 2016 book The Obesity Code.

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What is the Obesity Code?

Dr. Fung is an expert on intermittent fasting and low-carb diets, especially for treating people with type 2 diabetes

He graduated from medical school at the University of Toronto in Canada and completed his medical residency at the University of California, Los Angeles. He then returned to Toronto to practice as a nephrologist (a specialist in kidney diseases).

Dr. Fung found that most of his patients were also suffering from diabetes and obesity. For the first few years of his practice, he relied on conventional treatments, encouraging his patients to follow a low-fat diet and control their blood sugars while treating their kidney issues. His patients didn’t seem to be getting any better, though. So he set out to find a solution to the root cause of their problems. Dr. Fung eventually shared his methods in a 2016 book called The Obesity Code: Unlocking the Secrets of Weight Loss

It provides evidence-based advice for losing weight and managing your blood sugar by focusing on two main techniques:

In The Obesity Code, Dr. Fung discusses why traditional diets for obesity don’t work for most people. He feels this is because the cause of obesity is that overweight people have hormonal differences from non-overweight people. To treat obesity and reach a healthy weight, says Dr. Fung, you have to treat the hormonal imbalance at its root.

He also has two other books, The Complete Guide to Fasting and The Diabetes Code.

What diet does Dr. Jason Fung recommend?

Dr. Fung recommends intermittent fasting and a low-carbohydrate or ketogenic diet to help people lose weight and manage diabetes. 

Fasting is when you restrict your intake of food and drink for a period of time. It’s a common part of some religious beliefs, but even if you’re not religious, you’ve probably practiced it at least a few times in your life without really thinking about it. For instance, your healthcare provider has likely told you to fast before having a medical procedure or blood test (Sanvictores, 2021). 

Slightly more extended periods of fasting have been shown to provide health benefits and improve markers of health in your body, such as (Sanvictores, 2021):

Fasting affects your pancreas, the organ in your abdomen that helps to control your blood sugar levels. When your blood sugar is too high, your pancreas releases insulin to bring it back to normal. 

If your blood sugar is low, your pancreas tells your liver to release glycogen (the substance your body uses to store energy from the food you eat) to bring it back up and provide energy to the body. If your liver is low on glycogen because you’re fasting, your body will start to burn fat for energy. This is how fasting may help you reverse weight gain (Sanvictores, 2021). 

In The Obesity Code, Dr. Fung recommends occasional periods of fasting (intermittent fasting) alternated with periods of eating a low-carb or keto diet. Very low carbohydrate and high-fat diets such as the ketogenic diet have proven very effective for rapid weight loss (Masood, 2021).

Low carbohydrate diets help with weight loss by reducing levels of insulin. Insulin lowers your blood sugar, but it can also cause your body to store more fat. Studies have shown low-carb diets to work better than other dietary methods in producing rapid weight loss for the first 6–12 months (Oh, 2021).

How does intermittent fasting help you lose weight?

The hormone insulin helps control the amount of sugar (glucose) in your blood. If you become resistant to insulin, your body’s cells don’t respond the way they should to the insulin. Glucose can’t enter your cells as easily, and it builds up in your blood, which can eventually lead to type 2 diabetes.

Insulin resistance can happen for many reasons, including (Freeman, 2021):

  • Having excess bodyfat

  • Physical inactivity

  • Some types of medications

  • Nutritional imbalance (routinely eating a large amount of processed foods)

  • Aging

The best way to treat insulin resistance is with a low-calorie, low-carb diet and exercise. However, this can be difficult in some people with excess body weight (Freeman, 2021; Furmli, 2018).

Intermittent fasting can help promote your sensitivity to insulin by helping you restrict calories. While fasting, you don’t eat any food, but you can drink unlimited amounts of fluids with no added sugar, such as water, coffee, tea, and bone broth. The exact length of time that you fast for depends on your preferences and needs but can be anywhere from 16  hours to a few days (Furmli, 2018).

During your eating (feasting) periods, you’re encouraged to consume foods low in sugar and refined carbohydrates. This lowers your blood sugar and the amount of insulin that your pancreas releases. Snacking is discouraged (Furmli, 2018).

Intermittent fasting can lead to better blood sugar control, weight loss, better blood pressure, and might be easier to maintain long-term than other types of diets (Parmar, 2021)

Dr. Fung and other researchers documented the stories of three patients referred to Dr. Fung’s Intensive Dietary Management clinic in Toronto for insulin-dependent type 2 diabetes. All three patients were able to reverse their insulin resistance and stop using insulin. They also lost a significant amount of body weight (at least 10%) and reduced their waist circumferences (Furmli, 2018). These results are impressive, but it’s important to note that this is a very small sample size. 

How is the Obesity Code diet different from other diets?

Similar to other diets, the Obesity Code diet causes weight loss because you end up eating fewer calories than you burn. The difference is that the diet isn’t just about losing weight. 

Dr. Fung’s diet mainly focuses on lowering insulin levels in the body. This aids weight loss, but the primary benefits are that blood sugar levels normalize and inflammation decreases. 

Unlike many diets, in the Obesity Code diet, there are no recommendations for the number of macronutrients like protein, fat, and carbohydrates that you eat. Although you do end up eating fewer carbs and more protein and fat than is typical in an American diet, calorie counting isn’t required.

There are also no set meal plans or menus to follow when you break your fast. Depending on your perspective, this can be a plus or minus of the diet.

What are the pros and cons of the Obesity Code diet?

The pros of choosing a low-carb diet with intermittent fasting are that it’s a noninvasive option, is low cost, and you can customize a fasting schedule that meets your needs. 

However, like most diets, the Obesity Code diet can be challenging to maintain long term and it may not be appropriate for everybody. As mentioned above, there are also no set meal plans for your feast times, which can be difficult if you want to be told precisely what to eat and when.

Not every method of weight loss is suitable for every person. Your healthcare provider can help you decide if the diet from the Obesity Code is right for you and your goals.


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

November 04, 2021

Written by

Ellyn Vohnoutka, BSN, RN

Fact checked by

Steve Silvestro, MD

About the medical reviewer

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.

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