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Book Summary of The Obesity Code by Dr. Jason Fung

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In this book summary, we will find some simple explanations of biological factors and scientific studies that allow us to know the true cause of being overweight. We will understand the exact reasons for the obesity epidemic and why people often fail to lose weight.

What is the Book About?

Until recently, medical and nutritional science used to treat the subject of obesity in a very simplistic way. In the past you had been told that to lose weight, you need to eat less and to exercise more. You already know that this plan doesn’t work. Practice calorie reduction diets don’t work for most people because they just cause him too much hunger and anxiety.

Truth is that obesity is a disease that depends on many factors that we call it a multifactorial disease. To treat obesity we need to have a coherent structure that shows us how these multiple factors interact with each other and what role each one of them plays.

In this book summary of The Obesity Code, you’ll learn six simple steps that solve your weight problem.

About the Author

Dr. Jason Fung completed medical school at the University of Toronto and a fellowship in nephrology at the University of California. He founded the Intensive Dietary Management Program in Toronto that provides a unique treatment focus for type 2 diabetes and obesity. Dr. Fung lives in Toronto.

Book summary of The Obesity Code

Book Summary of The Obesity Code: Unlocking the Secrets of Weight Loss

The Obesity Epidemic

We need to understand the problem of obesity. You’ve probably received recommendations for low fat, low-calorie diet for several decades. This has been the official type of recommendation for weight loss. However, this type of recommendation probably didn’t work for you. To explain why just trying to reduce calorie intake doesn’t work to lose weight, we need to first understand what causes obesity.

The current concept of the disease has a rather simple yet incomplete response. We eat more calories than we burn, which leads to excess weight. Basically, when you eat too much and do too little exercise, you get fat. To find a real solution to the problem, it is important to recognize the immediate cause and the final cause.

The immediate cause is the cause that is responsible for the problem. While the final cause is the cause that initiated the chain of events that led to the problem. The most effective solution is to solve a final cause and not the immediate cause. Understanding the final cause can lead to real and effective solutions.

The same applies to obesity. The problem is: I’m gaining weight and I’m suffering from obesity. So the question is, what’s happening? What is the cause of the weight gain? What is the solution to that immediate cause? Balance the calories, make an effort. To follow the diet, eat less, and do more exercise.

Now the final cause will say you are obese due to a hormonal imbalance. The hormonal imbalance was caused by eating some nutrients in excess, out of the ideal ratio and the ideal time. Heavy and remodeling imbalance means you can’t control your appetite that leaves you too tired to get regular exercise. So the solution to the final cause is to balance the hormones by eating different foods and paying attention to the times or the meals.

The danger is to confuse the immediate cause of the final cause. The actual final cause of the obesity problem is hormonal imbalance. How can we handle it? By eating better foods in the right proportion and at the right time.

The Evolution of the Problem

The global obesity epidemic is a recent problem, because of this, different types of theories have been presented to try to understand why we get fat?

Carbohydrates, flour, starches, and sugars were the first ones to be accused as responsible for being overweight. This idea existed in the 1800s and low carbohydrates were created back in the day to treat obesity.

Years later new theories started to blame eating fats. The problem is that to reduce the proportional intake of fat in the diet, there is a need for a proportional increase in the intake of carbohydrates and proteins. But many protein-rich foods like meats and their products are also high in fat.

Since people wanted to reduce the dietary fat, carbohydrates have become disproportionately consumed more than others. And as carbohydrate consumption increased, the problem of obesity also increased.

One of the reasons to blame fats for increasing obesity is that one gram of fat contains more calories than one gram of carbohydrate or protein. The calorie calculations became important and they quickly developed it into all types of new recommendations and diets based on the maximum intake of daily calories.

The problem with these approaches is simply to blame the excess calories consumed. The belief at the time was that excessive consumption of fat was basically clogging the arteries and causing ordinary problems and leading to heart disease and death. This search for low calorie and low-fat diets ended up starting new food trends.

Companies in the food industry understood that it was necessary to modify their commercial advertisements and now also the composition of their products. Because the public’s attention was focused on the demand for low-fat foods.

Because of this, the protection and the consumption of sugar and refined grains have increased sharply around the world. We began to eat more and more bread, cereals and pasta. The new food trend was to exaggerate the number of whole grains as a symbol of eating healthy. In addition, to enhance the taste of food, more sugars were added to processed foods.

So for the next few decades, the population had reduced fat consumption and increased carbohydrate consumption. What was the result of this dietary change? Heart disease incidents have not declined, and the rate of obesity has increased ever since.

Eat Less, Exercise More, but Still Haven’t Lost Weight?

If you identify with this story, one day you’ll decide to start a diet; probably it’s a Monday. You put a lot of effort into eating less, and after a few days, you lose 2 pounds and you feel quite excited. You might even calculate how many days you’re going to need to keep this pace to reach your ideal weight.

For example, because you manage to lose 2 pounds in a week, you are going to need just to this diet and wait 10 weeks to drop 20 pounds and reach your ideal weight. But your calculations don’t work like that. 10 weeks go by and those 20 pounds are not burned off. The fat-burning rate has slowed down. Your body is not performing as well anymore, and after all, you’re feeding yourself too restrictively. This makes you tired, moody and more hungry than you can handle.

One day that you have less willpower, you’re going to fail to resist that temptation. You end up eating more than you should and then you regain the weight. When you realize that matters are getting out of control, you resolve to work even harder.

Maybe you seek inspiration by remembering the importance of losing weight for your health and your wellbeing.

However, the cycle repeats itself because it’s inevitable. By eating little, hunger dominates your ability to make decisions. Your body is tired and you find it difficult to do physical exercise. Sooner or later, you start eating more than you wanted, and you end up regaining the weight.

This is the free meals rebound or yoyo effect. In addition to returning to the previous weight, you still end up gaining more. This might leave you feeling frustrated and wondering what you did wrong. And there’s a huge load of emotional blame. The guilt gets even bigger when you imagine people around you feeling sorry for you or even blaming you.

Did you identify with that story? This is common among people who follow calorie restriction diets to lose weight. It happens mostly when the diet is based on low-fat food and the use of weight-loss supplements. So it is now time to make conscious decisions, based on good knowledge.

What is Your Body’s Response When You Stop Eating?

The truth is that your actions are heavily influenced by your hormones, not by lack of discipline or willpower or being lazy.

When you eat less, your body modifies the way you burn calories. This is one of the several problems of calorie-restrictive diets.

It is a mistake to assume that even with reduced calorie intake, your body will maintain the same calorie-burning rate. Multiple scientific studies have already shown a reduction in calorie intake causes an almost identical reduction in calorie expenditure. By consuming fewer calories, your body reacts in two ways:

1. The body reduces physical activities

This is why you find it difficult to continue your physical activities or exercises when you’re dieting. In this way, you maintain a balance between the amount of energy that you eat and the amount of energy that you burn. So you prevent yourself from collapsing.

2. A hormonal response that increases your hunger

The body asks us to eat more and we end up regaining all the weight that we have lost. To make matters worse this hunger hormone increases persist. This means you’re going to feel hungry for a long time, even after coming off of the diet.

The Myth of Exercise

Obviously regular exercise is very beneficial to health, but it is not the best answer to obesity. Even today many people believe that exercise is the main factor for weight loss and burning the excess calories that we eat. However, longterm studies have shown that exercise has minimal effect on weight loss.

Exercise helps. But there’s something more important. Your hormonal control.

Dieting = Doing Less Exercise

The explanation for exercise not being the main fat burning factor follows the very simple principle that the body is very efficient in maintaining stability. Being on a calorie restriction diet makes your body feel tired, and that reduces the number of calories that you burn.

Basically dieting means doing less exercise and exercising increases the amount of calories out and therefore the body feels more hungry. It increases the amount of calories gaining.

Exercising means eating more and when we exercise, actually our body will require the replacement of all that energy that was loosed. if you don’t eat enough, you’re going to feel exhausted and weak after a workout session. This is why we feel great pleasure when we’re feeding ourselves after doing exercise.

Obesity is a Hormonal Disease

All metabolic processes related to obesity are led by specific hormones. There is satiety regulating hormones that get rid of the feelings of hunger; Hunger is also caused by other hormones. All hormones act in our body with the intention to maintain our reference weight.

Perhaps the most important hormone for obesity is insulin, which is responsible for maintaining stable sugar levels.

When we eat and digest food, the carbohydrates are absorbed and passed into the bloodstream as glucose. Glucose is a sugar that is used by our body cells to keep us alive. However, glucose levels have to be carefully regulated. That is the function of the insulin that sets the blood sugar levels. When insulin levels are changed, the hormonal balances broken in several diseases such as type 2 diabetes and obesity can arise.

The key to weight control, therefore, is not balancing calories. You might be eating a lot of calories, but that is not the immediate cause. You have to find a way to fix the final cause, which is to readjust the hormones.

Implications of Stress and Lack of Sleep

Cortisol is also an older important hormone that plays a key role in gaining weight. Cortisol is also known as the stress hormone, which is responsible for all our emotional state of fight or flight.

Once released, cortisol causes increased blood glucose and first We have more energy available to the muscles. In modern times is very common that we have stress caused by anxiety, chronic stress, relationship problems, problems at work, a family argument, etc. It is cases we don’t really choose between fight or flight. There is no physical activity to use excess glucose. This gets worse because now I’m going to have also an excess of insulin, that is released because of that glucose.

That is why today we understand that stress is one of the factors that make you gain weight.

Insulin Resistance: the Real Villain

The constant consumption of high carbohydrate foods and stress subjects our body to high blood insulin levels. These high levels produce a natural resistance response. 

Those biological responses are called insulin resistance, which is associated with unwanted metabolic syndrome. The automatic response to the development of resistance is increased dosage. It’s a vicious cycle happening; The higher insulin levels cause greater resistance and the cycle continues.

Persistence Creates Resistance

Insulin resistance has two major components:

1. The first is the composition of foods that increase insulin levels. Depending on what you eat, your insulin level goes up.

2. The second component of insulin resistance has to do with “When you eat”. Depending on when you eat and how often you eat, your insulin levels will be constantly high.

The two prerequisites of developing insulin resistance are high insulin levels and persistence. So if you’ve spent all day eating meals, snacks and sweets all the time, you might end up spending 18 hours a day on a state of high blood insulin levels. This is called insulin persistence.

It is a huge problem today because now we are eating all the time. Social norm allows us for that and there are also many outdated experts that even recommend us to eat non-stop. It is also quite common to eat only three times a day.

There is a myth that says if you snack between meals, you’re going to eat less at lunch and dinner. This idea of eating between meals, helping us to lose weight has been proven wrong by two points related to the way insulin functions. Biscuits, cookies, sweet yogurt, chocolates and other foods that are rich in refined carbohydrates, increase insulin levels. By eating snacks and sweets all day long, we are creating conditions for the persistence of the high insulin level and persistence creates resistance.

What Mistakes Are We Making in Our Diet?

Consuming Too Much Sugar

Carbohydrates are sugars arranged in long chains and they play an important role in human nutrition providing energy and nourishment. Because of their importance, carbohydrates are one of the macronutrients along with protein and dietary fat.

We make mistakes about carbohydrates when we don’t differentiate between the different types of carbohydrates and metabolic reactions in our bodies. To understand the different types of carbohydrate sources we have to look at the glycemic index.

The glycemic index is a measure to control the rate at which certain foods raise blood sugar levels. The higher the glycemic index, the greater the ability to trigger insulin levels.

On the other hand, we have the fiber that is the non-digestible part of the food. Foods that are rich in fiber, take longer to digest. Therefore, sugars will take longer to reach the bloodstream, decreasing the unwanted insulin spikes.

It is no secret that eating sugar makes you fat. The problem is that sugar is hidden in foods that we wouldn’t even consider. But within carbohydrates, Fructose is the most dangerous sugar. Fructose is a reference to the natural sugar that is found in fruits but our intake of fructose is mainly in the form of processed foods. The problem with the consumption of fructose is industrialized products like corn syrup.

Excessive consumption of processed sugary foods not only creates obesity But it can also cause type 2 diabetes and fatty liver disease. If you want to avoid these illnesses, you should minimize the added sugars in your diet. Don’t substitute them for artificial sweeteners. Artificial sweeteners are not necessary. They don’t offer any nutritional benefits and their consumption promotes the need to eat more sweet foods all the time.

Proteins Should Be Well-Balanced

A common mistake is to assume that sugar consumption is the only thing that stimulates insulin secretion, but in order for us to have a complete picture, we should also understand that there are other factors that also affect insulin. During the digestion of fatty acids and proteins, the stomach is able to release hormones called incretin and incretin can trigger the production of insulin.

We must bear in mind, however, that incretins have a very desirable additional effect at the time of the weight loss. They are hormones naturally responsible for satiety. Therefore, we don’t want them excess or a lack of incretin, We just don’t want you to have those high protein diets, but we shouldn’t exclude the proteins and fats from our diets.

Overcome the Irrational Fatphobia

Unfortunately, the lack of good information has caused a huge collective phobia of naturally fatty foods. Dietary fats, and being blamed for being culprits of obesity and also ordinary heart disease.

There are scientific studies based on medical statistics that show eating good quality natural fats is not associated with being overweight or the development of coronary heart disease.

If we eliminate the fats from our food, we’re going to continue to be hungry and even end up eating more. Keep in mind that when we’re talking here about natural fats, we’re leaving out all kinds of processed-fat foods.

The Wise Solution

Now you know that obesity is a multifactorial disorder that goes far beyond the simplistic approach of calorie counting which is always solving the immediate cause. Above all, it’s necessary to understand the hormonal aspect, which is one of the final causes.

We learned that insulin is the main hormone that promotes weight gain. Therefore, the most sensible action to take is to decrease those high insulin levels.

Obesity Code Steps

A solution to the problem of weight gain is to take the following steps:

Step 1: Reduce the consumption of added sugars

Sugar stimulates insulin secretion and the consumption of sugar in excess not only makes you fat, but it also contributes to insulin resistance and metabolic syndrome. Obviously, the first thing you should do is to remove the sugar from the table. There’s no need to be adding extra sugar to food.

Read the labels of the packaged foods

Most processed products already contain a large amount of added sugar. Watch for pseudonyms such as glucose, fructose, maltose, dextrose, hydrolyzed starch, honey, sugar cane, corn syrup, corn sweetener, rice syrup, etc. At the end of the day, they’re all sugar.

Choose the right dessert

Try to eliminate high sugar desserts such as muffins, cakes, cookies, ice cream, sweets among others from your diet. You can replace them with fresh fruits, nuts, and dark chocolate.

Don’t eat between meals

Eating between meals is a big mistake. If you’re trying to control your insulin levels. Don’t keep snacking or eating treats.

Breakfast can be optional

Unless you’re a person with special needs, it is perfectly fine to skip breakfast and then break your fast at lunchtime,

Avoid drinks with sugar

The drinks we consume daily are the main sources of added sugars, so avoid all types of bottled drinks, smoothies, soft drinks and any juices with sugar.

What is advisable to drink? The best drink is natural water. Coffee and tea are also good without sugar.

Step 2: Reduce consumption of refined grains

If you reduce the consumption of white flour, you will have a better chance at losing weight.

Avoid processed foods based on flour and starch like bread, biscuits and all kinds of pasta. Carbohydrates should be ingested in their natural, whole, unprocessed form.

Vegetables such as eggplant, cabbage, spinach, carrots, cucumbers, and tomatoes are all-natural foods, rich in vitamins, fiber, and carbohydrates.

Step 3: Modify the protein intake

Due to the importance of proteins in our diet, you shouldn’t completely eliminate your intake. You shouldn’t abuse it either. It is advisable to adjust your consumption to represent between 20% to 30% of your total caloric intake.

Avoid protein bars, try to consume animal proteins and vegetables of natural origin such as meats, eggs, and beans.

Step 4: Increase the consumption of natural fats

Of these three macronutrients, carbohydrates, proteins, and fats, Dietary fat is the one that stimulates insulin the least. Therefore, it is a macronutrient that brings satiety without affecting your insulin levels. You can rely on the help of dietary fats to achieve the feeling of satiety, leading you to consume less and to assist in your weight loss plan.

Avoid refined oils. They’re obtained and predefined with all types of chemical solvents. Try to choose natural, unprocessed fats like olive oil, butter, coconut oil, and animal fat.

Nuts, avocados, and dairy products are also good sources of natural fats. Forget the myth that fat of these dairy products will make you fat.

Step 5: Increase your consumption of protective foods

Fiber and vinegar are true allies against insulin spikes and therefore they are protective foods against obesity. It is advisable to consume foods that are rich in fiber because fiber can reduce those stimulating effects of insulin.

Seasoning your foods with vinegar or even drinking apple cider vinegar diluted with water is generally a good practice.

Step 6: Fasting

To find a definitive answer to the problem of the insulin resistance that causes obesity, we must also add a piece to the puzzle, which is a solution found many centuries ago. It’s called fasting.

To have long term results when dieting, we must break the cycle of insulin resistance. We must go through recurring periods of very low insulin levels.

A recommendation is to perform intermittent fasting between 24 and 36 hours. It might seem strange, but fasting is an ancient and beneficial practice.

What is our body’s response to fasting? When we go for a fasting process, the body goes from burning glucose to burning fat. During fasting, insulin levels decrease, meanwhile, the levels of growth hormone increase. Growth hormones, in turn, increase the availability of fats as fuel. That helps to preserve muscle mass and reduce the stored fat.

Fasting can also help to increase adrenaline levels, increasing the metabolic rate. With fasting, metabolism and energy increase and blood sugar decreases.

Intermittent Fasting

Intermittent fasting is the great secret to losing weight and maintaining it.

We must balance or meals with periods of fasting.

Should you eat a lot during your birthday? Yes, of course, you should. These are moments of happiness or celebration of being together, but it is also appropriate to have some moments to fast. We cannot be stuffing ourselves all the time. We also can’t be fasting all the time.

How to fast?

  1. Drink water. Drink a glass of water every morning.
  2. Keep busy. That’ll help you to avoid thinking about food.
  3. Remember that hunger comes in waves. When hunger appears, slowly drink a glass of water. you can also drink coffee, green or black tea without sugar.
  4. If you feel dizzy, you can have a bone broth with sea salt. This will hydrate you and keep your salt levels stable.
  5. Choose wisely who you tell that you’re fasting.
  6. Give the necessary time. The first fasts are usually harder.
  7. When you’re not fasting, make sure that your diet is made up of quality and nutritious food
  8. Don’t overeat after fasting


Now, we know that obesity is not a problem caused by a calorie imbalance, but it’s because of the hormonal imbalance. The solution is not just to eat less and exercise more. It’s necessary to fix the longterm problem that is insulin resistance.

Remember that you should reduce your intake of refined grains and sugars and increase your intake of natural and good dietary fats.

Maximize your intake of protective foods such as fiber and vinegar. Also choose to eat natural and processed foods such as vegetables, seeds, nuts, eggs, and dairy products.

You’re going to switch between periods of eating and fasting. This way you can lead a healthier life. You lose weight and ward off diseases that are associated with obesity.

What did you learn from the book summary of The Obesity Code? What was your favorite takeaway? Is there an important insight that we missed? Comment below or tweet to us @storyshots.

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Book summary of The Obesity Code
Book summary of The Obesity Code

Adapted from Natugood YouTube Channel.

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