The Obesity Code Summary PDF Dr Jason Fung
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The Obesity Code Summary & Infographic | Dr. Jason Fung

Unlocking the Secrets of Weight Loss (Why Intermittent Fasting Is the Key to Controlling Your Weight)

The Obesity Code Summary PDF Dr Jason Fung

Life gets busy. Has The Obesity Code been on your reading list? Learn the key insights now.

In The Obesity Code summary, we’re scratching the surface. If you don’t already have Dr. Jason Fung’s popular book on health, fitness, and dieting, order it here or get the audiobook for free to learn the juicy details.


In this best-selling book, The Obesity Code, Dr. Jason Fung sets out an original and well-supported theory of obesity. Traditional thinking was that obesity is a function of calorie intake and exercise. However, Dr. Fung shares new insights into how proper nutrition and weight loss are functions of hormones. He focuses on insulin and how this powerful hormone appears to be the key to regulating metabolism. We can develop “insulin resistance,” which makes us fat.

Dr. Jason Fung’s theories use the latest scientific research into nutrition and obesity. This book is a step-by-step guide on losing weight and rebooting your health. 

We face an obesity epidemic. Despite all the diet advice available, we seem to get fatter. Dr. Fung brings a new perspective to the conversation on obesity with his bestseller, The Obesity Code.

“Not only full of insights but also surprisingly funny. Read it to understand why the world became fat, how to reverse the epidemic—and how to stay thin yourself.”

– Andreas Eenfeldt, MD, Founder of

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About Dr. Jason Fung

Dr. Jason Fung is the world’s leading expert on intermittent fasting and a low-carb diet. He specializes in treating type 2 diabetes. He has written three best-selling health books and co-founded the Intensive Dietary Management Program. He runs, which advises on weight loss and managing blood sugar, focusing on low-carbohydrate diets and intermittent fasting. The Daily Mail has credited him as “the doctor who invented intermittent fasting.”

He is also the scientific editor of the Journal of Insulin Resistance and the managing director of the nonprofit organization Public Health Collaboration (Canada), an international group dedicated to promoting sound nutritional information.

Dr. Fung’s goal is to share knowledge to help with weight loss to improve general health.

StoryShot #1: We Face an Obesity Epidemic

Obesity is an ever-present epidemic. Kidney specialists define obesity as being overweight to the point that it has negative health consequences. To reverse those negative effects, you must lose weight.

Dr. Fung notes that most doctors and dieticians prescribe eating fewer calories and burning even more calories to lose weight. These calories originate from food. A calorie is a unit of energy, calculated by burning foods in the lab and measuring the amount of heat released.

StoryShot #2: Don’t Focus on Calories

We begin with the history of counting calories. The practice began in the early 1900s with a series of bestsellers that claimed calories were responsible for weight gain. These books advised that the best way to lose weight was to cut calories.

This idea couldn’t be more far-fetched. These earlier theories are known as calorie-focused diets or caloric diets. They claim that the reasons you can’t lose weight are that you eat too much and are lazy.

In truth, this is far from the case.

StoryShot #3: Don’t Focus on Fat

In the late 1970s, fat became the new thing to avoid. Eating too much fat was linked to heart disease and is a key cause of obesity.

Everyone seemed to adopt a low-fat, high-carb diet in response to this new finding. The basis of the food pyramid soon shifted to bread, pasta, and potatoes. For decades, this high-carb diet has been considered the healthier solution. But this is also a mistake. 

StoryShot #4: Focus on Hormones

Dr. Jason Fung argues that neither calories nor fat are the main causes of weight gain. Rather, hormones are the primary driver of weight gain. The foods we eat contribute significantly to our hormones. There are also genetic factors in weight gain.

Hormones regulate your body fat. They control how much fat you store, where it gathers, and how your body ends up using it in the future.

So weight management goes beyond keeping tabs on calories in and out.

StoryShot #5: There Are Five False Assumptions About Calories

Five assumptions underlie “the calorie deception”.

The first is that you can cut calories by exercising. This calorie-deficit diet is often not sustainable, and most will fail at it. While you are likely to experience an initial weight loss, you are likely not to experience any long-term changes. If you cut incoming calories, you will eventually have to cut the calories you burn.

The second fallacy is how your metabolic rate is steady. This false idea comes from the common belief that you regularly burn a certain number of calories. But this belief cannot consider all the variables of your metabolism. You need to be aware of your total baseline energy expenditure, which can vary by 50%.

The third assumption is that we cannot control calorie storage. We assume we can control our eating habits. However, our bodies are the primary driving factors in when we eat and how much we consume. Body-fat regulation is automatic, like breathing. 

The fourth is that fat grows inexplicably. This couldn’t be further from the truth. Nothing in our bodies happens by accident. Hormones control everything within your body.

The biggest of the five assumptions is that all calories are alike. Proteins, fats, and carbs all contain calories, and your body uses these building blocks in different ways. Each stimulates a different hormone, thus uniquely contributing to obesity.

A group of young adults eating fast food outside – an example of unhealthy eating habits that can cause obesity.
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Unhealthy eating habits

StoryShot #6: Hormone Imbalance is to Blame for Obesity

Hormonal imbalance is responsible for obesity.

Hormones are molecules that deliver messages to cells. An example is insulin, which lets cells know when to take glucose out of the blood and use it as energy.

High insulin levels encourage fat storage, while low levels are responsible for fat burning. Also, when your insulin level is high over an extended period, your body is likely to store more fat. It is possible to gain weight simply by prescribing you insulin. The hormone is powerful enough to outweigh what you eat or how many times you work out. Too much insulin over an extended time will likely make you obese and unhealthy.

Numerous studies back this theory. The moment insulin levels are reduced, your body automatically stops the process of fat storage, and ultimately, you lose weight.

StoryShot #7: Social Factors Contribute to Obesity

Social factors make it harder to lose weight. The food industry influences you through “triggering messaging”.

Big companies make money by selling you profitable food. It doesn’t matter whether it is healthy or not.

The food industry has three myths. The first is that snacking is good for your health. The second is that breakfast is the most important meal of the day. The third is that adding fruits and vegetables to your diet makes it healthy. Big companies design these myths to help them sell their products.

There is a link between socioeconomic status and obesity. States with the highest poverty levels also have the highest levels of obesity. The reason is that the cheapest and most filling foods are often refined carbohydrates. These are cheapest because there are agricultural subsidies for corn and wheat growers. This amounts to state-sponsored obesity. It targets the poorest and most vulnerable members of society.

StoryShot #8: Carbohydrates Are the Secret Assassin in Our Diets

Carbohydrates drive up blood sugar, which increases insulin levels. Over time, these high amounts of insulin lead to increased fat storage and ultimately weight gain.

Sugar is the chief villain. Its most common forms are glucose and fructose. Glucose drastically drives up blood sugar levels. Your body is then forced to churn out more insulin, which contributes to sugar getting into the cells. Fructose has a different effect. It goes directly to the liver instead of being stored in the cells. The liver then breaks the fructose down and ultimately stores the excess as fat. The result is often a fatty liver, which contributes to insulin resistance. 

Insulin resistance causes your body to produce more insulin, creating a significant spike in insulin levels. The effect is an even greater storage of fat in the liver and an even greater insulin resistance.

This is a vicious cycle, where your liver constantly fights for its life due to your carbohydrate intake. The remedy is to reduce sugar in your diet. This will lower your insulin levels, ultimately causing significant weight loss.

You do not have to cut out carbs altogether. Some carbohydrate-containing foods can be healthy choices. These include eggplant, kale, spinach, carrots, broccoli, peas, Brussels sprouts, tomatoes, asparagus, bell peppers, zucchini, cauliflower, avocados, lettuce, beets, cucumbers, watercress, and cabbage.

StoryShot #9: Know Which Carbs to Target

Don’t assume you can eliminate sugar from your diet. You can introduce healthier options and target the unhealthiest foods to get rid of.

The glycemic index helps identify good carbs and bad carbs. When a carb has a high glycemic index and load score, it is likely to have the greatest impact on your blood sugar. Ultimately, this means greater insulin levels.

Avoid high-glycemic foods like white bread, processed cereals, soft drinks, and candy. Substitute for low glycemic index foods like vegetables and some fruits.

Doctor measuring a man’s waistline and tummy area using a measuring tape
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Knowing the proper way to combat obesity

StoryShot #10: Learn the Complete Solution to Obesity

All diets work and fail in equal measure. They fail because weight loss is not permanent. For weight loss to be permanent, you have to lose weight until you reach your body’s set weight. In essence, this then resets your brain’s ‘fat thermostat.’

To lose weight:

  1. Reduce added sugars, simple carbs, and highly processed grains.
  2. Make proteins 30% of your total calories.
  3. Consume natural fats.
  4. Increase your consumption of fiber and vinegar.

But this is only one part of the solution.

By the time you become obese, your body has likely already had long-term insulin resistance. Your body will also adopt other mechanisms that make losing weight nearly impossible.

To offset this situation, Dr. Jason Fung advises us to consider fasting. You can fast for a full day or break this up into intermittent fasting according to your eating habits. The idea is to extend the periods without eating. To break insulin resistance and lose weight, intermittent fasts of twenty-four to thirty-six hours are effective.

Additionally, exclude from your diet any foods that cause insulin resistance. Cut back on added sugars, processed foods, and simple carbs. Instead, consider increasing your fat, fiber, and vinegar intake. The ultimate diet would be a low-carb, mid-protein diet full of healthy fats and fiber.

Female stepping on a weighing scale with a measuring tape in front
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Know the true causes of your weight gain.

Final Summary and Review 

The Obesity Code is a timely read that offers insight into the obesity epidemic. It delves into the current myths of weight loss and offers incredible insights into factors that lead to obesity.

Evidence suggests we should move away from traditional diets based around cutting fat or calories. Instead, we should reduce unhealthy carbohydrates and consider intermittent fasting. With this book, you have the simple steps and tools to make lasting change in your life.

Key takeaways include: 

  1. Don’t focus on calories or fat to lose weight.
  2. Carbohydrates, particularly sugar, are responsible for excessive weight gain.
  3. The food industry is partly responsible for the increase in obesity.
  4. Hormones, particularly insulin, are responsible for weight gain and are integral to weight loss.
  5. Low-carb, mid-protein diets are best for losing weight.
  6. Fasting is crucial in keeping insulin at optimum levels.
  7. Substitute added sugars, processed foods, and simple carbs with healthy fats, fibers, and vinegar.
  8. Avoid high-glycemic foods like white bread, processed cereals, and soft drinks.
  9. Snacking is not good for you. Breakfast is not the most important meal of the day. Adding fruits and vegetables to your meals doesn’t make them healthy.
  10. Both biology and socioeconomic factors are responsible for obesity.  

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We rate this The Obesity Code 4.4/5.

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Editor’s Note

This article was first published in April 2022. It was revised and expanded on 13/1/2023.

The Obesity Code Infographic

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The Obesity Code by Dr Jason Fung Diet Plan Infographic
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PDF, Free Audiobook, Infographic, and Animated Book Summary of The Obesity Code

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  1. My psychiatrist/MD recommended your book. I’ve ordered it based on the summary plus the cookbook. I don’t believe I understand, at this point, how long a person is to fast? 24 -36 hours seems too long?

    1. You start from Four Hour, slowly add time. I started from 4 hour now a days i am doing 200 hour fast. no issur

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