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

by Jason Fung

Many of the effects of aging may result from low growth hormone levels.

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.

The most potent natural stimulus to growth hormone secretion is fasting.

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

Modern medicine’s greatest challenges are metabolic diseases: obesity, type 2 diabetes, high blood pressure, high blood cholesterol, and fatty liver, collectively known as metabolic syndrome.

the Western diet, with its abundance of sugar, high fructose corn syrup, artificial flavors, artificial sweeteners, and overdependence on refined grains.

There are only three macronutrients: carbohydrates, proteins, and fats.

Extra-virgin olive oil is not the same as trans-fat-laden margarine, even though both are pure fat.

Protein from wild salmon is not the same as highly refined gluten (which is a protein even though it’s found in grains).

but one hundred calories of a green salad does not have the fattening effect as one hundred calories of chocolate chip cookies.

Therefore, the best advice focuses on eating or not eating specific foods, not specific nutrients.

Fasting, of course, is the ultimate weapon in your arsenal when it comes to lowering insulin levels—since all foods stimulate insulin to some degree, the best way to lower insulin is to eat nothing at all.

What humans haven’t evolved to eat are highly processed foods. During processing, the natural balance of macronutrients, fiber, and micronutrients is completely disrupted.

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

Processing transforms relatively innocuous vegetable oils into fats that contain trans fats, toxins whose dangers have now been well recognized.

If it has a nutrition label, it should be avoided. Real foods, whether broccoli or beef, have no labels.

The true secret to healthy eating is this: Just eat real food.

it’s most important to avoid sugars and refined grains, such as flour and corn products.

Foods high in monounsaturated fats, such as olive oil, nuts, and avocados, which were previously shunned, are now considered “superfoods” because they are so healthy.

Partially hydrogenated vegetable oils—found in foods such as shortening, deep-fried foods, margarine, and baked goods such as cakes and cookies—contain trans fats, which our bodies do not handle well.

Eat whole, unprocessed foods. Avoid sugar. Avoid refined grains. Eat a diet high in natural fats.

Balance feeding with fasting.

Intermittent fasting can be successfully implemented with either short fasts (less than twenty-four hours) or longer fasts (more than twenty-four hours).

Extended fasting (more than three days) can also be safely used for weight loss and other health benefits.

we encourage consuming plenty of noncaloric liquids (water, tea, coffee) and homemade bone broth, which is full of nutrients.

Actually, fasting has the opposite effects—lower glucose, lower blood pressure, and lower risk of cancer.

Fasting does not make you tired. Fasting does not burn muscle. There is no starvation mode from fasting where you shrivel up into the fetal position on your couch.

Rather, fasting has the potential to unleash the anti-aging properties of growth hormone without any of the problems of...

Dr. Fung supports any whole-food approach that limits processed foods in addition to fasting, without dictating which diet is best.

Indeed, fasting is the most time-honored and widespread healing tradition in the world.

In spiritual terms, it is often called cleansing or purification, but practically, it amounts to the same thing.

Fasting is not so much a treatment for illness but a treatment for wellness.

With no storable grains, and few other foods that stayed fresh for very long, most of our ancestors experienced both feast and famine on a regular basis.

However, there was a critically important factor of their diet that he completely dismissed: most of the population of Crete followed the Greek Orthodox tradition of fasting.

Buddhist monks are known to abstain from eating after noon, fasting until the next morning.

This fits with their core beliefs in moderation and austerity.

One early fasting advocate was Hippocrates of Cos (c. 460–c. 370 BC), widely considered the father of modern medicine.

In fact, fasting can be considered an instinct, since all animals—dogs, cats, cattle, sheep, and also humans—avoid food when sick.

So fasting can be considered a universal human instinct for handling multiple kinds of illnesses. It’s truly ingrained in human heritage, and it’s as old as mankind itself.

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.

If 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.

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

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.

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—

Most of the calories we spend each day are not used for exercise but for these basic functions.

This is what most people mean when they say that metabolism slows down with age, and it contributes to the well-known tendency of older “snowbirds” from the Northeast and Canada to retire in warm places like Florida and Arizona.

Daily caloric reduction has been well documented to cause a dramatic reduction in BMR.

reducing calories consumed to approximately 1500 calories a day for a long stretch of time will result in a 25...

Reduced metabolism makes us generally cold, tired, hungry, and less energetic—our bodies are essentially conserving energy by not burning calories to keep us warm and moving.

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