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

by Jason Fung

Grains enjoy substantial government subsidies, making them far cheaper than other foods.

Even low-carbohydrate diets, which are proven to result in more weight loss than other diets in the short term, show the same inexorable plateau and weight regain.

The Centers for Disease Control and Prevention in Atlanta closely tracks obesity trends in the United States, and according to its data, in 2015, no state had an obesity rate below 20 percent. Only twenty years earlier, in 1995, no state had an obesity rate above 20 percent.

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.

The USDA’s first Dietary Guidelines for Americans was released in 1977. It recommended that Americans adjust their diets to meet two specific goals: increase consumption of carbohydrates and reduce intake of total fat.

Since 1970, consumption of vegetables, fruits, and grains has increased, and consumption of red meat, eggs, and animal fats has declined, just as the USDA’s dietary guidelines recommended. But the promised benefits never materialized.

Since 1970, Americans have largely followed the government’s dietary recommendations. At the same time, the obesity epidemic has exploded.

More recently, in 2015, researchers in the United Kingdom reviewed the weight-loss rates of more than 175,000 obese men and women over the previous nine years. The probability of achieving a normal weight by caloric reduction alone was 0.8 percent in women and 0.47 percent in men. So the best-case scenario using conventional calorie-counting methods is a 99.2 percent failure rate.

A study of Biggest Loser contestants showed that in thirty weeks of filming, average weight dropped from 329 pounds to 202 pounds. That’s an average decrease of 127 pounds! Body fat dropped, on average, from 49 percent to 28 percent. Almost all of the weight lost was fat mass, as opposed to lean tissue, or “fat-free mass”. (There is inevitably some lean tissue lost along with fat, but this is generally skin and connective tissue, not necessarily muscle.) Wow! Amazing! Unfortunately, those results simply didn’t last. 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.

there are two distinct ways energy is stored in the body: as glycogen in the liver and as body fat.

Not only do low insulin levels allow access to the fat freezer, they actually trigger fat-burning for energy. If insulin levels are abnormally low, then fat is continually burned.

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.

When stored glycogen gets low, your

body senses it and starts to get antsy. It triggers hunger signals, so you want to eat more. If you don’t eat enough to fill up the glycogen stores but your insulin remains high, body fat can’t be released. The body’s only remaining option i...

the high insulin levels tell your body to hang onto body fat and simultaneously trigger the body to lower your metabolism.

For some of us, changing what we eat is clearly not enough.

When we eat, insulin rises and blocks fat-burning, and the body instead burns glucose, which is now freely available from the ingested food. But of the three macronutrients—carbohydrates, fat, and protein—carbohydrates stimulate the production of insulin the most.

Insulin is the main driver of obesity and diabetes. A very low carb diet can reduce insulin by more than 50 percent, but you can go another 50 percent by fasting.

During fasting, unlike during caloric reduction, metabolism stabilizes or even goes up to maintain normal energy levels. Adrenaline and growth hormone increase to maintain energy and muscle mass.

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

Bariatric surgery is also spectacularly successful for the reversal of type 2 diabetes. In one study, a stunning 95 percent of adolescent patients with type 2 diabetes who underwent bariatric surgery saw their disease reversed.

Body fat is composed mostly of triglycerides, which are molecules made of one glycerol backbone to which three fatty acids of varying lengths are attached.

During fat-burning, the triglyceride molecule is broken down into the glycerol backbone and the 3 fatty acids.

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.

the brain still requires glucose to function normally during fasting, but we do not need to eat glucose. We can manufacture enough glucose to power the entire body simply from body fat.

The World Health Organization released its first global report on diabetes in 2016. It’s clear from the report that diabetes is an unrelenting disaster. Since 1980, the number of people afflicted with diabetes has quadrupled.

2016, and there are more Americans with prediabetes and diabetes than without:

The most obvious benefits of fasting are that it helps with weight loss and type 2 diabetes, but there are many other benefits, including 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.

So what actually happens during caloric deprivation is that the brain maintains or even boosts its abilities.

Humans, like all mammals, have an increase in mental activity when hungry and a decrease when satiated.

As the amount of blood going to the digestive system is increased to handle all that turkey and pie, less blood is available to go to the brain.

Our ancient ancestors grew more alert and active when hungry so that they could find their next meal—and the same thing still happens to us.

Aging rats started on intermittent fasting regimens markedly improved their motor coordination, cognition, learning, and memory. Interestingly, there was even increased brain connectivity and new neuron growth from stem cells.

Compared to normal mice, mice on an intermittent fasting regimen showed less age-related deterioration of neurons and fewer symptoms of Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease.

insulin levels have an inverse correlation to memory—that is, the lower the insulin level, the more memory improves.

a higher body mass index is linked to decline in mental abilities and decreased blood flow to those areas of the brain involved in attention, focus, reasoning, and more complex, abstract thought.

There appears to be significant research indicating a dramatic drop in inflammation, improvements in insulin signaling, and a near total “reset” of immune function with fasts of 3–5 days. Abnormal and or pre-cancerous cells appear to be pushed towards apoptosis, which essentially selects for healthy cell types.

Autophagy is a form of cellular cleansing:

Increased levels of glucose, insulin, and proteins all turn off autophagy.

the constant intake of food, such as snacking throughout the day, suppresses autophagy.

For people with chronic inflammatory and/or neurological conditions, fasting can help accelerate autophagy and the body’s clearing-out of old, damaged tissue. The body engages in “housecleaning” all the time, but when it gets a break from the constant digestion of large amounts of food, it may be able to focus more energy on repair and restoration.

Since it triggers both the breakdown of old cellular parts and the creation of new ones, fasting may be considered one of the most potent anti-aging methods in existence.