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

by Jason Fung

If insulin levels are abnormally low, then fat is continually burned.

Insulin resistance, sometimes called prediabetes or metabolic syndrome, is the most common situation where insulin levels are persistently kept abnormally high.

Insulin Resistance

The way to successfully break the insulin resistance cycle is not to continually increase insulin levels but to drastically decrease insulin levels.

When our cells become less sensitive to insulin, the body’s knee-jerk reaction is to increase insulin production.

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

High Insulin + Reduced Calories = Slowing Metabolism

(incorrect!) idea that all calories are equal and stored in one single compartment, so if you’re using more calories than you’re consuming, you must be burning body fat.

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.

If you don’t eat enough to fill up the glycogen stores but your insulin remains high, body fat can’t be released.

decrease your metabolism so that you’re burning less energy.

And as insulin resistance progresses, the resulting high insulin levels make it harder and harder to access the fat stores.

The body always wants to stay at a certain weight,

That’s why, after weight loss, we become hungrier and our metabolism relentlessly slows, so that we have to eat even less just to maintain our lower weight. That’s the body trying to get us to gain weight to get us back to our set weight.

This is why insulin resistance plays such a crucial role in obesity: the high insulin levels tell your body to hang onto body fat and simultaneously trigger the body to lower your metabolism.

Now, let’s say you want to lose weight, so you reduce your daily calories to 1,200.

The major problem, as you can see, is not that there aren’t enough calories available. There are 350,000 calories stored away in the fat freezer. The problem is that these calories are not available for the body to use. The main issue is how to get access to the energy locked away in the fat. Insulin is the crucial factor to consider here, not the number of calories you eat.

their metabolism slowed down in response to caloric reduction.

Reducing your caloric intake by 800 calories per day, as the contestants did, means that you feel cold, lethargic, and tired as your body starts to slow down to conserve energy.

Since all foods raise insulin levels, the best answer is to completely abstain from food.

So why can’t a successful weight-loss strategy be simply eliminating all carbohydrates instead of fasting?

Reducing refined carbohydrates reduces insulin.

protein, especially from animal source...

Fas...

keeps insulin...

The very low carb diet does remarkably well, providing you 71 percent of the benefits of fasting, without actual fasting.

A very low carb diet can reduce insulin by more than 50 percent, but you can go another 50 percent by fasting.

metabolism stabilizes or even goes up to maintain normal energy levels. Adrenaline and growth hormone increase to maintain energy and muscle mass. Blood sugar and insulin levels go down as the body changes from burning sugar to burning fat.

A study of type 2 diabetics showed that a very low carb diet does reduce insulin compared to a standard diet, but fasting reduces it even more.

If you maintain a constant reduced-calorie diet, the body will quickly adapt to it. Energy expenditure (metabolism) declines to match the reduced intake. Weight plateaus, then is regained. This is not because you have stopped your diet but because your body has now adapted to it.

Restricting some foods all the time differs from restricting all foods some of the time.

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

So, yes, 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.

Head-to-head studies reveal that fasting is actually superior to bariatric surgery in both weight loss and reduction in blood sugars. Both methods are also effective for type 2 diabetes.

FASTING AND CORTISOL

fight-or-flight response—it’s a survival adaptation.

cortisol levels are generally unaffected.

Type 2 diabetes, on the other hand, is a dietary and lifestyle disease.

the body stops being able to respond to insulin’s signals after prolonged exposure to excess insulin.

typically diagnosed after age fifty

the “overstrained” pancreas could no longer keep up with the demands of an excessive diet.

Consider, for example, the effect of wartime starvation on type 2 diabetes. During both World War I and World War II, the mortality rate from type 2 diabetes dropped precipitously.

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.

it appears that this train (cell) is now resistant to insulin’s signals.

One solution is to hire subway pushers to shove people into the trains. This was implemented in New York City in the 1920s, and while the practice has since died out in North America, subway pushers still exist in Japan, where they are euphemistically called “passenger arrangement staff.”

If the normal amount of insulin can’t get the glucose in, then the body calls for reinforcements: even more insulin.

But the main cause of the insulin resistance is that the cell was already overflowing with glucose.

However, there is a natural limit. At that point, even extra insulin will not be able to move more glucose into the cell.

hyperinsulinemic people finally tap into their stored body fat for energy—

Mammals generally respond to severe caloric deprivation by reducing organ size, with two prominent exceptions: the brain and, in males, the testicles.