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

by Jason Fung

Prolonged studies of fasting have found no evidence of electrolyte imbalances—the body has mechanisms in place to keep electrolytes

stable during fasting.

they found that hunger was virtually absent during these prolonged fasts.

Most people expect that a period of fasting will leave them feeling tired and drained of energy. However, the vast majority of people experience the exact

opposite: they feel energized and revitalized during fasting. Partly this is because the body is still being fueled—it’s just getting energy from burning fat rather than burning food. But

Human growth hormone (HGH)

Excessively low growth hormone levels in adults leads to more body fat, less muscle mass, and decreased

bone density

Growth hormone also increases the availability of fats for fuel by raising levels of key enzymes,

burning fat reduces the need for glucose, this helps maintain stable blood sugar.

growth hormone in older people with low levels has significant anti-aging benefits.

six

months of growth hormone replacement increased lean mass (bone and muscle) by an astounding 3.7 kilograms (8.2 pounds), even as fat mass d...

Meals very effectively suppress the secretion of growth hormone, so if we’re eating three meals per day, we get effectively no growth hormone during the day. Worse, overeating suppresses growth hormone levels by as much as 80 percent.

The most potent natural stimulus to

growth hormone secretion is fasting. In one study, over a five-day fasting period, growth hormone secretion more than doubled. During fasting, in addition to the usual early-morning spike of growth hormone (pulsa...

Interestingly, very low-calorie diets are not able to provoke the same growth hormone response.

And a 1992 study showed a fivefold increase in growth hormone in response to a two-day fast.

Our body has evolved to handle natural foods, and when we feed it unnatural ones, the result is illness.

Just eat real food.

Eat whole, unprocessed foods. Avoid sugar. Avoid refined grains. Eat a diet high in natural fats. Balance feeding with fasting. !

fasting has the opposite effects—lower glucose, lower blood pressure, and lower risk of cancer. Plus, we reap all the benefits of the increased growth hormone.

Fasting does not make you tired. Fasting does not burn muscle.

fasting helps with weight loss (Chapter 5) and type 2 diabetes (Chapter 6), boosts brainpower and slows aging (Chapter 7), and improves heart health (Chapter 8). All of these benefits are achieved without drugs, supplements, or any costs.

Before the modern era, food availability was unpredictable and highly irregular. Drought, war, insect infestations, and disease all played a part in restricting food, sometimes to the point of starvation. So did the seasons: during the summer and fall, fruits and vegetables were plentiful, but during the winter and spring, they were scarce. Periods without food could last weeks or even months.

As human societies developed agriculture, these periods of famine were gradually reduced and eventually eliminated.

It has been practiced by virtually every culture and every religion on earth.

Three of the most influential men in the history of the world, Jesus Christ, Buddha, and the Prophet Muhammad all shared a common belief in the healing power of fasting. In spiritual terms, it is often called cleansing or purification, but practically, it amounts to the same thing.

fasting and prayer are often methods of cleansing and renewing

the soul. Symbolically, believers empty their souls so that they may be ready to receive God. Fasting is not so much about self-denial but about a reaching for spirituality and being able to commune with God and hear his voice.

Traditional Ayurvedic medicine also ascribes the cause of many illnesses to the accumulation of toxins in the body and prescribes fasting to cleanse these toxins.

The ancient Greeks believed that medical treatments could be observed from nature, and since humans, like most animals, naturally avoid eating when they become sick, they believed fasting to be a natural remedy for illness.

Think about the last time you had the flu, or even a cold. The last thing you probably

wanted to do was eat. So fasting can be considered a universal human instinct for handling multiple kinds of illnesses.

The ancient Greeks also believed that fasting improved mental and cognitive abilities,

Think about the last time you ate a huge Thanksgiving meal. Did you feel more energetic and mentally alert afterwards?

Or did you feel sleepy and a little dopey?

After a large meal, blood is shunted to your digestive system to cope with the huge influx of food, leaving...

best of all medicines is resting and fasting.”

Benjamin Franklin

“A little starvation can really do more for the average sick man than can the best medicines and the best doctors.”

Mark Twain

For most of human history, large amounts of food were not readily accessible all throughout the day.

Intermittent fasting was likely a regular part of human evolution, and it’s possible our bodies—and brains—have come to expect periods of food scarcity. Because we are blessed with abundant food all year round in the twenty-first century, we now have to make a special effort to impose food scarcity upon ourselves for therapeutic purposes.

metabolic diseases such as type 2 diabetes are caused by eating too much, then logically, the solution is to eat little to balance it out. What could be simpler?

Although fasting was widely practiced historically, most of us today grew up believing some fundamental myths about the dangers of fasting.

Most people mistakenly believe fasting is detrimental to health. The truth is quite the opposite—there are a significant number of health benefits,

“Starvation mode” is the mysterious bogeyman always raised to scare us away from missing even a single meal. Why is it so bad to skip a meal? Let’s get some perspective here. Assuming we eat three meals per day, over one year, that’s a little over a thousand meals.

To think that fasting for one day, skipping three meals of the one thousand, will somehow cause irreparable harm is simply absurd.

The idea of “starvation mode” refers to the notion that our metabolism decreases severely and our bodies “shu...

We can test this notion by looking at the 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. Most of the calor...

If short-term fasting dropped our metabolism, humans as a species would not likely have survived.