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

by Jason Fung

evolutionary standpoint. Suppose food is scarce and difficult to find. If cognitive function started to decline, the mental fog would make it that much harder to find food.

ABEL JAMES

when I began fasting through the morning, I immediately noticed a significant increase in mental focus, energy, and productivity.

Despite popular belief, it’s not the tryptophan in the turkey causing that postprandial drowsiness—

It’s just the sheer amount of food.

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

Think about a time that you were really, really hungry. Were you tired and sluggish? I doubt it. You were probably hyperalert, your senses sharp as a needle.

If missing a single meal reduced our energy and mental acuity, we would have even more trouble finding food, making it more likely that we would go hungry again, leading to a vicious cycle ending in death.

Fasting and hunger energize us and activate us to advance towards our goal, despite popular misconceptions to the contrary.

Aging rats started on intermittent fasting regimens markedly improved their motor coordination, cognition, learning, and memory.

increased brain connectivity and new neuron growth from stem cells.

(BDNF), which supports the growth of neurons and is important f...

In animals, both fasting and exercise significantly increase the beneficial BDNF effects in ...

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

Increased levels of glucose, insulin, and proteins all turn off autophagy. And it doesn’t take much. Even as little as 3 grams of the

amino acid leucine can stop autophagy.

The mammalian target of rapamycin (...

since there’s plenty of energy to go around, there’s no need to eliminate the old subcellular machinery.

As the body senses the temporary absence of nutrients, it must prioritize which cellular parts to keep.

The oldest and most worn-out cellular parts get discarded, and amino acids from the broken-down cell parts are delivered to the liver, which uses them to create glucose during gluconeogenesis.

Whether the body has stored energy is irrelevant for mTOR and therefore for 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.

This is why the strongest stimulus to autophagy currently known is fasting,

Alzheimer’s is characterized by the abnormal accumulation of amyloid beta (Aß) proteins in the brain,

Normally, clumps of Aß protein are removed by autophagy:

in Alzheimer’s disease, autophagy is impaired and the Aß protein remains inside the brain cell,

We’re learning that mTOR plays a role in cancer biology, and mTOR inhibitors have been approved by the Food and Drug Administration for the treatment of various cancers.

Fasting’s role in inhibiting mTOR, thereby stimulating autophagy, provides an interesting opportunity to prevent cancer’s development.

Dr. Thomas Seyfried, a professor of biology at Boston College, have proposed a yearly seven-day water-o...

high triglycerides can be treated with a low-carbohydrate diet, which lowers the rate at which the liver creates triglycerides.

their hunger diminish,

They often report that despite their own expectations, they are eating less than half their usual amount of food on a daily basis, yet they feel completely full.

Studies of circadian rhythm confirm that for most people, hunger is very low first thing

in the morning, even though it has been twelve to fourteen hours since the last meal.

hunger is partly a learned phenomenon.

the sound of a dinner bell can create hunger

Pavlov’s dogs.

Salivation, pancreatic fluid secretion, and insulin production increase immediately upon the expectation, not the actual delivery, of food.

This helps synchronize the gut response and the incoming food, and is known as the cephalic phase response.

If we consistently eat every morning at 7:00 a.m., then we develop a conditioned response to that time and become hungry at 7:00 a.m.,

That’s not to say we don’t get hungry at all—we do, but not simply because we have a conditioned response to a certain time or occasion. Instead, we get hungry because we are hungry.

It’s also helpful to avoid artificial sweeteners. Even though they contain no calories, they may still kick off the cephalic phase response, stimulating hunger as well as insulin production. I don’t recommend artificial sweeteners during fasting for this very reason. Recent studies confirm that diet sodas are generally not helpful for weight loss, probably because they trigger hunger but don’t satisfy it.

artificial sweeteners can kick off the cephalic phase response, triggering hunger and insulin production, so I recommend avoiding them during a fast.

There are certainly people who feel that adding sweeteners to their coffee helps them lose weight by increasing compliance with their fast, and if it works for you, great.

But my best advice is to try to fast without the use of sweeteners. If you cannot do that, then try adding a small amount. However, if it makes fasting harder or...

The secret is to understand that hunger comes in waves. You just need to ride out the waves.

What’s the best way to endure the wave of hunger during fasting? Drinking green tea or coffee is often enough. By the time you’re finished, the hunger has passed and you’ve gone on to the next thing to do that day.

Hunger is not a continuously growing phenomenon. It will build up, peak, and then dissipate, and all you have to do is ignore it.

having a list of things to do as a distraction. I kept the list on my refrigerator,

Hunger is a state of mind, not a state of stomach.