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

by Jason Fung

After just 14 weeks following the Wild Diet with intermittent fasting, Kurt lost an astounding 87 pounds.

combining a high-fat, low-carb nutrition plan with intermittent fasting and strategic strength training can result in rapid and dramatic fat loss.

(carrying 300 pounds of weight takes more energy than carrying 200 pounds, so a small slowdown is expected—when we refer to slowing metabolism, we mean the slowdown in excess of that).

Figure 5.13. Bariatric surgery patients do not show a decrease in their basal metabolic rate, unlike people on simple caloric reduction (see Figure 5.8).

And because fasting may be considered a potential stressor, some are concerned that it may raise cortisol levels.

Two weeks of intermittent fasting caused no increase in cortisol levels, and even a seventy-two-hour fast failed to raise cortisol levels significantly. While levels may vary among individuals, on the whole, elevated cortisol levels are not a major concern during fasting.

You’ll probably eventually experience a weight-loss plateau as the weight lost during fasting begins to match the amount regained during eating. (The only way not to plateau at all is to continually fast for weeks or months at a time; otherwise, reaching an

equilibrium is inevitable.) Changing either your fasting regimen or diet, or both, may help. Some patients increase fasting from twenty-four-hour periods to thirty-six-hour periods, or try a forty-eight-hour fast. Some try eating only once a day, every day. Others try a continuous fast for an entire week. Any of these can be effective; the key is simply to change the fasting protocol.

(It’s unclear why Dr. Allen thought whiskey was necessary.)

As we discussed in Chapter 5, both fasting and bariatric surgery result in a sudden, severe restriction of foods, so it’s not surprising that fasting has a similar effect. In fact, it’s been known to cure type 2 diabetes for over a hundred years. Joslin thought the truth of it was so obvious that studies were not even needed. Interestingly, visceral fat, fat that’s stored in and around the organs, likely plays a large role in type 2 diabetes. It’s more harmful to health and, unfortunately, more common than subcutaneous fat. Fasting and bariatric surgery both preferentially reduce visceral fat. 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. This was due to wartime food rationing, which resulted in a sustained, severe reduction of calories. Figure 6.3 shows the co-occurrence of wartime sugar rationing and a drop in deaths from diabetes, but keep in mind that it wasn’t just sugar that was rationed—almost all foods were restricted, resulting in a sustained, severe calorie reduction similar in magnitude to Fredrick Allen’s infamous starvation diet. Figure 6.3. Diabetes mortality improved during wartime rationing. Source: Cleave, The Saccharine Disease.

Source: Lingvay, “Rapid Improvement in Diabetes After Gastric Bypass Surgery: Is It the Diet or Surgery?”

Let’s consider an analogy. Imagine the cell to be a subway train. Glucose molecules are the passengers waiting to get inside the train. Insulin gives the signal to open the train doors, and the passengers—the glucose molecules—march in a nice orderly manner into the empty subway train. Normally, it

doesn’t really require much of a push to get this glucose into the cell.

But what happens if the train is not empty? What if it’s already jam-packed full of passengers? Insulin gives the signal to open the door, but the passengers waiting on the platform cannot enter. From the outside, it appears that this train (cell) is now resistant to insulin’s signals.

Insulin is the body’s subway pusher, shoving glucose into the cell no matter the consequences. 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.

Because the cell is overfilled with glucose, glucose spills out of the cell, leading to increased blood glucose levels. This leads to the diagnosis of type 2 diabetes.

If the core issue is that glucose is overfilling the cells, then the solution seems rather obvious: get all that glucose out of the cells! Pushing more in, as with insulin treatments, will only make things worse.

reversed. Mischief managed.

If you are not taking any blood sugar medications, then there is no particular reason to monitor your blood sugar during fasting: your blood sugar may drop slightly but will remain in the normal range.

In a process called apoptosis, also known as programmed cell death, cells that reach a certain age are programmed to commit suicide. While this may sound kind of macabre at first, the process constantly renews cell populations, making it essential for good health. But when just some cellular components need to be replaced, a process called autophagy kicks in.

They may also be incorporated into new proteins. It’s important to note that the dormancy of mTOR is only related to short-term nutrient availability and not the presence of stored energy, such as liver glycogen or body fat. Whether the body has stored energy is irrelevant for mTOR and therefore for autophagy.

Autophagy also plays an important role in the prevention of Alzheimer’s disease. Alzheimer’s is characterized by the abnormal accumulation of amyloid beta (Aß) proteins in the brain, and it’s believed that these accumulations eventually destroy the synaptic connections in the memory and cognition areas. Normally, clumps of Aß protein are removed by autophagy: the brain cell activates the autophagosome, the cell’s internal garbage truck, which engulfs the Aß protein targeted for removal and excretes it, so it can be removed by the blood and recycled into other protein or turned into glucose, depending upon the body’s needs. But in Alzheimer’s disease, autophagy is impaired and the Aß protein remains inside the brain cell, where eventual buildup will result in the clinical syndromes of Alzheimer’s disease.

Furthermore, it’s not the cholesterol particle itself that’s cause for concern—remember, that’s identical in both LDL and HDL. It’s instead the lipoproteins carried along with the cholesterol particle that determine whether it’s good or bad. Reducing the cholesterol in our foods makes little or no physiological difference, a fact that was proven long ago.

It is still running strong, now with its third generation of participants.

“there is a slight negative association between daily intake of total fat (and also of animal fat) with serum cholesterol level.”