The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting

by Jason Fung

But those feasts should be followed by fasts.

And when you fast regularly, you do not need to feel guilty about enjoying one of life’s little pleasures, because you can make up for it.

The quickest and most efficient way to lower insulin and insulin resistance is fasting.

Fasting has no ceiling, which offers significant therapeutic flexibility.

However, with fasting, all you need to do is increase the amount of time spent fasting. The longer you go, the more likely you are to lose weight—and it will happen eventually.

Fasting can be done at any time. There is no set duration. You may fast for sixteen hours or sixteen days. You can mix and match time periods.

Once again, because fasting is about not doing something, it simplifies our life. It adds simplicity where other diets add complexity.

Here is the biggest advantage of all: fasting can be added to any diet.

Six years after their almost miraculous weight loss, thirteen of the fourteen contestants studied had regained the weight they’d lost. This is a failure rate of 93 percent.

The main reason for the weight regain is that the contestants’ metabolisms had slowed significantly (we’ll explain why later in this chapter).

Danny Cahill, the winner of Season 8, lost 239 pounds during the competition. However, his body was now burning 800 calories ...

Whether calories are stored as glucose, which is used for immediate energy; glycogen, which is used in the intermediate time frame; or fat, which is long-term energy storage, all calories are treated equally.

It is more accurate to use a two-compartment model, because there are two distinct ways energy is stored in the body: as glycogen in the liver and as body fat.

When we eat, our body derives energy from three main sources: glucose (carbohydrates), fat, and protein.

Only two of these are stored for later use, glucose and fat—the body can’t store protein, so excess protein that can’t be used...

Glucose is stored in the liver as glycogen, but the liver’s capacity for stor...

Dietary fat is absorbed directly into the bloodstream without passing through the liver, and what’s n...

Both body fat and glycogen are used for energy in the absence of food, but they aren’t used equally or at the same time.

The body prefers to use glycogen for energy rather than body fat.

The two compartments, the fridge and the freezer, are not used simultaneously but sequentially

In essence, the body can burn either sugar or fat, but not both.

When we are not eating, insulin levels are low, allowing full access to the fat freezer—the body is able to easily get at the stored fat.

With low insulin levels, you don’t even have to completely empty the glycogen refrigerator before opening the fat freezer, since it’s so easily accessible.

Not only do low insulin levels allow access to the fat freezer, they actually trigger fat-burning for energy.

Insulin inhibits lipolysis—it stops the body from burning fat.

High insulin levels, which are normal after meals, signal our body to store some of the incoming energy.

This doesn’t just happen after meals, however—we also see this in diseases of too much insulin.

Insulin resistance, sometimes called prediabetes or metabolic syndrome, is the most common situation where insulin levels are persistently kept abnormally high.

One of insulin’s main jobs is to move glucose from the bloodstream into the cells so that it can be used for energy.

Normal amounts of insulin are not able to move glucose into cells, leading to a buildup of glucose in the blood. To compensate, the body must produce extra insulin to force the glucose in. This leads to constant high insulin levels, which blocks fat-burning.

The way to successfully break the insulin resistance cycle is not to continually increase insulin levels but to drastically decrease insulin levels.

Our body is constantly receiving the signal to store energy as fat and is never told to burn fat.

Insulin plays a crucial role in the decision of which fuel to burn.

To burn fat, two things must happen: you must burn through most of your stored glycogen, and insulin levels must drop low enough to release the fat stores.

difficult to access fat stores. The high insulin is instructing the body to store energy, not burn it.

There are 350,000 calories stored away in the fat freezer.

When we eat, insulin rises and blocks fat-burning, and the body instead burns glucose, which is now freely available from the ingested food.

Refined carbs and sugar in particular have the greatest effect on insulin, so a diet low in these is most certainly a great start for breaking the insulin resistance cycle and losing weight.

Since all foods raise insulin levels, the best answer is to completely abstain from food. The answer we are looking for is, in a word, fasting.

The very low carb diet does remarkably well, providing you 71 percent of the benefits of fasting, without actual fasting.

The short answer is that when you’re eating regularly, even if you’re eating fewer calories, you’re not getting the beneficial hormonal changes of fasting.

The inability of most diets to reduce insulin resistance is exactly why they eventually result in weight regain.

Another way to look at this is that most diets ignore the biological principle of homeostasis.

To prevent the body from adapting to the new weight-loss strategy and maintain weight loss requires an intermittent strategy, not a constant one. This is a crucial distinction.

Restricting some foods all the time differs from restricting all foods some of the time.

WHAT HAPPENS WHEN WE BURN FAT: KETONES AND KETOACIDOSIS

A ketogenic diet gets its name from ketone bodies. These are substances the body produces during fat-burning; they’re what fuels the brain when glucose is scarce.

Of course, fasting causes the body to burn fat, too—and that means it also results in the creation of ketones.

However, certain cells are not able to burn fat, including the inner part of the kidney (renal medulla) and red blood cells. To supply the glucose those cells need, the liver uses the glycerol backbone to manufacture new glucose molecules.

Ketone bodies produced during fat-burning fill that gap, and the brain becomes powered mostly on ketones, which supply up to 75 percent of its energy needs.