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

by Jason Fung

The underlying cause of obesity turns out to be a hormonal, rather than a caloric, imbalance. Insulin is a fat-storage hormone. When we eat,

type 2 diabetes, however, insulin levels are not low but high. Blood sugar is elevated not because the body can’t make insulin but because it’s become resistant to insulin—it doesn’t let insulin do its job. By prescribing

Excessive insulin causes obesity, and excessive insulin causes insulin resistance, which is the disease known as type 2 diabetes.

why keto is so great for fasting: being in ketosis teaches your body to burn fat for fuel rather than sugar, and since that’s what your body has to do during fasting, if you’re already in ketosis,

My HDL-C, known as the “good” cholesterol, predictably fell from 61

to 50 during the fast. One of the basic materials needed for HDL cholesterol is fat, especially saturated fat. So when you don’t consume any food at

the most stunning result of all of these tests was the Lp(a) (Lipoprotein a), a risk factor in the development of cardiovascular disease. My initial Lp(a) of 441 was extremely high (always

but suffice to say, if you’re struggling with obesity and/or type 2 diabetes, fasting can have an incredible effect on weight and blood sugar. I’ve seen it with my own eyes, even when I was still skeptical about fasting.

Abel lives with his wife in Austin, Texas. He enjoys strong coffee and cheesecake, preferably together. Visit his website, fatburningman.com, for more.

Real people need real food! You can read her blog and find more of her work at tuitnutrition.com.

overcome health problems and achieve optimal health and well-being. Visit his website, DrRuscio.com, for more.

Health goes far beyond diet, so Dr. Bert does too. To see more, look for his TEDx talk, “Did I Enrich Today?,” which has over 235,000 views, or visit his website, bertherring.com.

Zoe and Sagan. Visit his website, robbwolf.com, to learn more.

For example, you may fast between dinner and breakfast the next day, a period of twelve hours or so. In that sense, fasting should be considered a part of everyday life. Consider the term breakfast. The word refers

So what’s the problem? Nobody makes money when you fast. Not Big Food. Not Big Pharma. Nobody wants you to find out the ancient secret of weight loss.

Figure 1.1. The average number of meals and snacks consumed by adults increased from 3 per day in 1977–78 to almost 6 per day in 2003–06.

Some even feel that snacking more will help lose weight, as ridiculous as that sounds. Consider my son’s typical schedule.

When we eat, we ingest more food energy than we can immediately use. Some of this energy needs to be stored away for later. The key hormone involved in both the storage and use of food energy is insulin, which rises

during meals. Both carbohydrates and protein stimulate insulin. Fat triggers a far smaller insulin effect, but it’s rarely eaten alone. Insulin has two major functions. First, it allows the body to immediately start using food energy. Carbohydrates are absorbed and rapidly turned into glucose, raising blood sugar levels. Insulin allows

glucose to enter directly into most cells of the body, which use it for energy. Proteins are broken down into amino acids and absorbed, and excess amino acids may also be turned into glucose. Protein does not raise blood glucose, but it can raise insulin levels. The effect is variable, and it s...

as some carbohydrate-containing foods. Fats are directly absorbed as fat and have m...

So you see, the body really only exists in two states—the fed (high-insulin) state and the fasted (low-insulin) state. Either we are storing food energy or we

2. The postabsorptive phase (six to twenty-four hours after beginning fasting): At this point, blood sugar and insulin levels begin to fall. To supply energy, the liver starts to break down glycogen, releasing glucose. Glycogen

stores last for approximately twenty-four to thirty-six hours.

3. Gluconeogenesis (twenty-four hours to two days after beginning fasting): At this point, glycogen stores have run out. The liver manufactures new glucose from amino acids in a process called gluconeoge...

persons, glucose levels fall but stay within t...

Refined carbohydrates tend to raise insulin the most and fatty foods the least, but insulin still goes

The opposite of insulin sensitivity, high insulin resistance, is the root problem in type 2 diabetes and has also been linked to a number of diseases, including:

Lowering insulin also rids the body of excess salt and water because insulin is well known to cause salt and water retention in the kidneys.

Growth hormone also increases the availability of fats for fuel by raising levels of key enzymes, such as lipoprotein lipase and hepatic lipase. Since burning fat reduces the need for glucose, this helps maintain stable blood sugar.

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

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

There is nothing inherently unhealthy about carbohydrate-containing foods. The problem arises when we start changing these foods from their natural state and then consuming them in large amounts. The same also applies to processed

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

For everyone, but especially for those with metabolic syndrome, it’s most important to avoid sugars and refined grains, such as flour and corn products. These are more fattening

But not all fats are so innocent. 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. Trans fats raise LDL (“bad”) cholesterol and lower HDL

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

Turning his genius to medicine, he once wrote, “The best of all medicines is resting and fasting.”

So we have two incontrovertible facts: Fact #1—Over the past twenty years, conventional weight-loss advice has called for eating less and moving more. Fact #2—Over the past twenty years, obesity rates have exploded.

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 right away is converted to glucose. Glucose is stored in the liver as glycogen, but the

Think of glycogen as a refrigerator. It’s designed for short-term storage of food; it’s very easy to move food in and out, but the storage space is limited. Body fat, on the other hand, is more like a basement freezer. It’s

One of insulin’s main jobs is to move glucose from the bloodstream into the cells so that it can be used for energy. If you have insulin resistance, your cells are no longer sensitive to insulin.

since insulin resistance develops in response to persistently high insulin levels, we must create recurrent periods of very low insulin levels.

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.

Cortisol is a hormone that’s released during times of stress, whether physical or psychological. This activates the fight-or-flight response—it’s a survival adaptation.

until the twentieth century, for two reasons: first, it is typically diagnosed after age fifty (in fact, it used to be called adult-onset diabetes) and average life expectancy was lower than it is today, and second, food was not nearly as available and plentiful. The combination of relative food scarcity

It is well known and well accepted that type 2 diabetes is a disease of insulin resistance. One of insulin’s main jobs is to move glucose from

the blood into the tissues, which use it as energy. When insulin resistance develops, the normal level of insulin is not able to move glucose into tissue cells. Why?