Book notes: The Obesity Code by Jason Fung

The Obesity Code: Unlocking the Secrets of Weight Loss by Jason Fung, MD book review summary and key ideas.

The Obesity Code: Unlocking the Secrets of Weight Loss by Dr. Jason Fung

The Obesity Code: Unlocking the Secrets of Weight Loss by Jason Fun, MD book review summary.


“Everything you believe about how to lose weight is wrong. Weight gain and obesity are driven by hormones – in everyone – and only by understanding the effects of insulin and insulin resistance can we achieve lasting weight loss.

In this highly listenable and provocative book, Dr. Jason Fung sets out an original, robust theory of obesity that provides startling insights into proper nutrition. In addition to his five basic steps – a set of lifelong habits that will improve your health and control your insulin levels – Dr. Fung explains how to use intermittent fasting to break the cycle of insulin resistance and reach a healthy weight – for good.” -Audible

~If you enjoy my summary, please consider buying me a coffee via my Ko-Fi link (click the button below) or become a recurring donor as a YBC Scholar! 📖 🎓

I appreciate every donation as it goes directly to the maintenance costs of my blog and creation of new content. 😊

Buy Me a Coffee at

Opening thoughts:

I picked this book up because I think it was on a two for one sale on Audible and the synopsis seemed interesting. It had good reviews and it seems like it would be very insightful to learn about because it is something everyone deals with.

Key notes:

  • Chapter 1: How obesity became an epidemic
  • There was hardly any correlation between a child environment and their obesity
    • A study showed that a child is more likely to resemble their parents
  • 70% of your tendency to gain weight is determined by your parentage
    • Obesity is overwhelmingly inherited
  • Humans are not genetically predisposed to over eat and become fat
  • In humans, evolution did not favor obesity but rather leanness
  • One false assumption is that calories in and calories out are independent factors
    • In reality, they are dependent as calories in affects calories out
  • Because hormones regulate fat growth, obesity is a hormonal problem
  • The assumption that a calorie is a calorie is false
    • Different types of calories will provoke different responses in your body such as a calorie of olive oil versus a calorie of sugar
  • Thermodynamics, a law of physics, has minimal relevance to human biology for the simple reason that the human body it’s not an isolated system
    • Energy is constantly entering and leaving
  • The body responds to reduce caloric intake by reducing energy expenditure in different systems light body heat, hair and a nail replacement, strength and endurance, and heart volume and stroke
  • The theory that reducing caloric intake leads to weight loss is false
  • The low-fat, low-calorie diet has been proven to fail
    • Eating less does not result in lasting weight loss
    • It does not work
  • Exercise is not the only variable in total energy expenditure
  • In regards to weight loss, diet is 95%
    • Exercise has a lot of benefits, but not a lot towards weight-loss
  • Studies have also shown that increasing calories doesn’t necessarily lead to weight gain
  • Eating more is the consequence of weight gain
    • Eating more doesn’t make us fat, getting fat makes us eat more.
  • Obesity is a hormonal dysregulation of fat mass
    • Obesity is caused by a body set weight that is too high because of a hormonal imbalance in the body
  • Under normal conditions low insulin levels encourage glycogen and fat burning
  • High insulin secretion has long been associated with obesity
    • Obese people secrete much higher levels of insulin than do those of normal weight
  • Numerous studies show that insulin causes obesity
  • The most crucial question in obesity is “how to reduce insulin?” 
  • Cortisol is the so-called stress hormone which mediates the flight or fight response, a set of physiological responses to perceived threats.
    • Cortisol raises insulin
      • Stress causes weight gain
      • Sleep deprivation leads to weight gain
  • Getting good sleep is essential to any weight loss plan 
  • The carbohydrate-insulin hypothesis states that refined carbohydrates and sugars cause spikes in insulin levels
    • Highly refined carbohydrates don’t trigger the satiety hormones and cause an “addicted” feeling
    • These foods activate reward centers in our brains and make us feel comfort
    • Refined carbohydrates are not natural foods but are instead highly processed
      • There toxicity lies in that processing
  • Sugar seemed to contribute more to obesity than other refined carbohydrates
  • Insulin resistance causes high insulin levels, and high insulin levels causes obesity
  • Obesity is time dependent
    • The longer you stay obese, the harder it is to lose weight
  • The body builds resistance to whatever it is exposed to
    • Therefore, more insulin causes more insulin resistance
    • This causes more insulin to be produced, and the cycle continues
  • The staring point of the vicious cycle is high insulin levels
  • Eating frequent meals does not have a significant effect on your overall metabolism
    • Persistent, high insulin levels throughout the day is what causes an increase in insulin resistance
  • Another myth is that eating frequently controls hunger, but there is hard to find evidence to support this
  • The increase in eating opportunities has led to persistence of high levels of insulin
  • The idea of breakfast being the most important meal is mostly a North American custom
  • The Dawn Phenomenon: every morning before we wake up, a natural circadian rhythm jolts our bodies with a heavy mix of growth hormone, cortisol, epinephrine, and norepinephrine, adrenaline
    • This cocktail stimulates the liver to make new glucose essentially giving us a shot of good stuff to wake us up
  • We don’t need food when we wake up
    • Morning hunger is often a learned behavior starting from childhood
    • Most of us aren’t naturally hungry in the morning
  • Breakfast eaters tend to eat more and more often
    • Furthermore, many people admit to forcing themselves to eat breakfast because they’ve been told it’s the healthy choice
  • You should eat more healthy foods like fruits and vegetables, but only if it replaces unhealthy food in your diet
    • Replace, don’t add
  • High insulin resistance is known as Type 2 diabetes
  • Persisting high levels of insulin causes obesity and Type 2 diabetes
  • Fructose: the most dangerous sugar
    • Fructose overconsumption leads directly to insulin resistance
  • If you want to avoid weight gain, remove all added sugars from your diet
    • Don’t replace them with artificial sweeteners
  • Vinegar has been shown to have a mild weight loss affect
    • Vinegar reduces the glycemic index of carbs and reduces insulin resistance
  • Over 70% of insulin fluctuations is not due to blood glucose levels
  • If you are not hungry, don’t eat
    • Your body’s ability to make you feel satiety protects you from weight gain
    • All foods stimulate insulin so all foods can cause weight gain
    • Stick to real, natural foods
  • Studies showed that saturated fat had no correlation with coronary heart disease
  • Eating fat doesn’t make you fat, but may protect you against it
    • Eating fat together with other foods tends to decrease glucose and insulin spikes
    • Dietary fat would be expected to protect against obesity
  • The low-fat diet paradigm for weight loss was proven to be a failure
  • All diets work because they all address a different aspect of the disease of obesity
    • But none of them work for very long because none of them addresses the totality of the disease
    • Obesity has a multifactorial nature
  • Sugar directly produces insulin resistance
    • With no redeeming nutritional qualities, added sugars are usually one of the first foods to be eliminated in any diet
    • Some of the best replacements for desserts are:
      • fresh seasonal fruits with whip cream
      • nuts and cheeses
      • 70% or more dark chocolate
  • If your goal is weight loss, your first major step must be to severely restrict sugar
    • Don’t replace sugar with artificial sweeteners as they also raise insulin as much as sugar
  • Don’t snack
    • Grazing is one of the greatest weight loss myths and the opposite of virtually all food traditions
    • Don’t eat snacks. Simplify your life
  • Make breakfast optional
    • If you’re not hungry, don’t eat breakfast. But if you are, it’s okay
    • Just don’t sacrifice quality for convenience in heavily processed, packaged, sugar added, refined carb foods
  • Aside from water, coffee and tea can have some protective effects against Type 2 diabetes
  • Reduce your consumption of refined grains, such as white flour, stimulate insulin to a greater degree than virtually any other food 
  • The toxicity in much western food lies in the processing rather than in the food itself
    • The carbohydrates in western diets are heavily skewed towards refined grains and are thus highly obesegenic
  • Moderate your protein consumption
  • Increase your consumption of natural fats
  • Dietary fats is the least likely to stimulate insulin of the three macronutrients
  • Increase your consumption of protective factors
  • Five basic steps of weight loss:
    1. Reduce your consumption of added sugars
    2. Reduce your consumption of refined grains
    3. Moderate your protein intake
    4. Increase your consumption of natural fats
    5. Increase your consumption of fiber and vinegar
  • There’s actually a lot more agreement with many mainstream diets than we think
    • But the discord is what fuels sales in books and advice

“There is nothing new except what has been forgotten”

Marie Antoinette
  • Insulin resistance is a problem of meal timing
  • Fasting is one of the oldest remedies in human history and has been part of the practice of virtually every culture and religion on earth
    • Fasting is an inherent human instinct especially when we are sick
    • Fasting is the most efficient and consistent strategy to decrease insulin levels 
    • The body preserves muscle mass until fat stores become so low that it has no the choice
  • Feasting follows fasting, and fasting follows feasting
    • Diets must be intermittent, not steady
  • It is clear that there are no lasting negative side effects to fasting.
    • On the contrary, it appears to have extraordinary health benefits
    • Fasting can be combined with any diet imaginable
  • There are two main considerations for proper food choices:
    1. What to eat
    2. When to eat
  • Fasting is defined as the voluntary act of withholding food for a specific period of time
    • Non-caloric drinks such as water and tea are permitted. And absolute fast refers to the withholding of both food and drink
  • Make sure to break your fast gently and don’t over eat
  • Sample foods for breaking your fast include a handful of nuts or a salad
  • During fasting, it is important to recognize that hunger does not persist but instead comes in waves
    • Staying busy during a fasting day often works
  • Starting your day with a glass of cold water helps
  • Fasting is actually an ideal time to exercise 

Main ideas / Themes:

  • Because hormones regulate fat growth, obesity is a hormonal problem
  • Eating less does not result in lasting weight loss
  • In regards to weight loss, diet is 95%
  • Cortisol raises insulin
  • Getting good sleep is essential to any weight loss plan
  • The longer you stay obese, the harder it is to lose weight
  • We don’t need food when we wake up
  • If you want to avoid weight gain, remove all added sugars from your diet
  • Reduce your consumption of refined grains
  • Sugar directly produces insulin resistance
  • If you are not hungry, don’t eat
  • Stick to real, natural foods
  • All diets work because they all address a different aspect of the disease of obesity
  • Don’t snack
  • Insulin resistance is a problem of meal timing
  • Fasting is the most efficient and consistent strategy to decrease insulin levels
  • Make sure to break your fast gently and don’t over eat

Closing thoughts:

I loved this book! Many of the same ideas in this book are also in my other favorite “diet” book The Warrior Diet, but this book goes more into the science and studies.

I’ve been doing Intermittent Fasting since last April, so I can safely say that I’ve implemented some of these suggestions and did have really good results. It’s neat to read about the science behind the strategies and practices I’ve been using, like why it works and how it affects weight/fat.

I think all of the studies about how eating more or eating less actually doesn’t affect your weight in the long run was mind blowing for. Another point was how it’s all about your insulin resistance, and that is affected by what you eat (mostly sugar and refined carbs) and when you eat (timing). If you can get these two down, you’ll be able to control insulin and insulin resistance.

I also really enjoyed the paradigm shift about how its okay to be hungry, its natural, and in fact its the most effective way to detox and balance out so much eating that our society does.

This is one of those books that I would highly recommend to anyone and everyone because the content is hyper-relevant to all people.


Obesity is simply a hormonal problem caused by insulin resistance. This can be fixed by eating real food, removing added sugars, and utilizing intermittent fasting (meal timing).



Similar books:

Try Audible for audiobooks 📚🎧

Personal recommendation: For the last 6 years, I’ve used Audible to listen to all of my favorite books. It’s easy to use, cost-effective, and they have the best library of audiobooks.

If you use my affiliate links below, not only will you get a special offer, but it’ll help support the costs to maintain this blog! 😊👇

Try Audible and Get Two Free Audiobooks

Audible Gift Memberships 

Donate to this blog!

Please consider a small donation to help support my blog ^_^ I love providing free book notes and other content. Any donations help me maintain my website and create content consistently. Thanks everyone for the continued support!


9 thoughts on “Book notes: The Obesity Code by Jason Fung”

  1. I’ve been listening to this audio book and it’s great but I haven’t really been able to take notes. Your notes helped out alot. Thank you!


Leave a Reply to yolocruz Cancel reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: