Health Skills: Jason Fung and Jimmy Moore teach you how to heal yourself by doing nothing


Before reading any diet books, I suggest you start with fasting. Fasting allows you to continue your current eating habits and prepare you for a specific diet. After reading this book:

  • You will know the history of fasting 
  • You will know the biggest myths surrounding fasting
  • You will know the benefits of fasting

Something specific I really like

There are many myths surrounding fasting, I really like how the authors debunked the biggest ones.  Like…when you hear the word fasting, you probably think “starving”. You are not alone, I used to think that too. But in reality, there’s a big difference between fasting and starving, as the authors put it:

Fasting is completely different from starvation in one crucial way: control. Starvation is the involuntary abstention from eating. It is neither deliberate nor controlled. Starving people have no idea when and where their next meal will come from. This happens in times of war and famine, when food is scarce. Fasting, on the other hand, is the voluntary abstention from eating for spiritual, health, or other reasons. Food is readily available, but you choose not to eat it. No matter what your reason for abstaining, the fact that fasting is voluntary is a critical distinction.

What are the main myths that scare people from the oldest health tool? According to the authors, there are 5 major ones:

  • Myth #1: Fasting Puts You in “Starvation Mode”
  • Myth #2: Fasting Makes You Burn Muscle
  • Myth #3: Fasting Causes Low Blood Sugar
  • Myth #4: Fasting Results in Overeating
  • Myth #5: Fasting Deprives the Body of Nutrients

Myth #1: Fasting Puts You in “Starvation Mode”

Before exploring this myth any further, we need to define “starvation mode”. According to the authors, it means that that our metabolism decreases severely and our bodies “shut down” in response to fasting. To debunk this myth, we need to look at our basal metabolic rate (BMR), which measures the amount of energy that our body burns in order to function normally—to keep the lungs breathing, brain functioning, heart pumping, kidneys, liver, and digestive system all working, and so on. 

The authors found that the opposite is true, metabolism revs up, not down. Four days of continuous fasting increased BMR by 12 percent. This means that the body has started to switch over from burning sugar to burning fat, with no overall drop in energy.


Myth #2: Fasting Makes You Burn Muscle

One persistent myth of fasting is that it burns muscle, that our body, if we’re not eating, will immediately start using our muscles as an energy source. This does not actually happen.

The human body evolved to survive periods of fasting. We store food energy as body fat and use this as fuel when food is not available. Muscle, on the other hand, is preserved until body fat becomes so low that the body has no choice but to turn to muscle. This will only happen when body fat is at less than 4 percent. (For comparison, elite male marathon runners carry approximately 8 percent body fat and female marathoners slightly more.) The whole process represented graphically: 

Myth #3: Fasting Causes Low Blood Sugar

When glucose is not available, the body begins to use alternative sources of energy. Remember fat? Our bodies use it to produce ketone bodies, which are able to cross the blood-brain barrier to feed the brain cells. Up to 75 percent of the brain’s energy requirements can be met by ketones. Of course, that means that glucose still provides 25 percent of the brain’s energy requirements. Luckily our liver uses the byproducts of ketone production to create glucose (gluconeogenesis). This means that we have plenty of fuel when no food is available. Even prolonged fasting won’t send blood glucose levels dangerously low.

Myth #4: Fasting Results in Overeating

Studies of caloric intake do, in fact, show a slight increase on the first day after fasting. On the day after a one-day fast, average caloric intake increases from 2,436 to 2,914. But if you factor in what would have normally been consumed during that two-day period, 4,872 calories, there is still a net deficit of 1,958 calories. The increased calories don’t come close to making up for the lack of calories on the fasting day.

Myth #5: Fasting Deprives the Body of Nutrients

There are two main types of nutrients, micronutrients and macronutrients. Micronutrients are vitamin and minerals that are provided by the diet and are required for overall health. Macronutrients are proteins, fats, and carbohydrates.

Micronutrient deficiency is rare in the developed world. With shorter fasting periods (less than twenty-four hours), there is ample opportunity before and after the fast to eat nutrient-dense foods to make up for missed meals. For longer fasts, it is a good idea to take a general multivitamin. The longest fast recorded lasted 382 days, and a simple multivitamin prevented any vitamin deficiencies.

Of the three major macronutrients, there are no essential carbohydrates that the body needs to function, so it is impossible to become carbohydrate deficient. However, there are certain proteins and fats that we have to get in our diet. These are called the essential amino acids (the building blocks of proteins) and essential fatty acids. These cannot be manufactured by the body and must be obtained in the diet.

The body normally loses both essential amino acids and essential fatty acids in urine and stool. During fasting, it reduces these losses to hang onto much of the necessary nutrients. Bowel movements usually decrease during fasting—since no food is going into the stomach, there is less stool formation—and this helps to prevent loss of nutrients in the stool.

Of course, no matter how good the body is at hanging onto necessary nutrients, fasting means we’re not consuming essential fatty acids and amino acids. Before and after fasting, it can be helpful to follow a low-carbohydrate diet, which increases the percentage of fats and proteins consumed, so the body has more stored up for a rainy day.

Why fasting?

After tackling the myths surrounding fasting, it’s time to consider the biggest benefits of fasting. These are:

  • It helps with weight loss and type 2 diabetes.
  • Autophagy (a cellular cleansing process).
  • Lipolysis (fat-burning).
  • Anti-aging effects, and neurological benefits

In other words, fasting can benefit your brain and help your body stay younger. To find the perfect cycle (12, 16, 24 hours, etc.), pick up the book and start experimenting.