Fasting?

This is to "drink the wind to avoid grain" ah.

This question is not difficult to answer.

This is because many people have practiced fasting for 1 week or more, either for religious reasons or for "health" reasons.

So there is a relatively clear answer to this question.

Before giving the answer, let's theorize a bit.

If we don't consider other factors, just from the perspective of energy balance, fasting for 7 days is equivalent to 7 days without exogenous energy supplementation.

Assuming that the body maintains light physical activity, it consumes about 2500 kcal per 24 hours.

If these 2500 kcal were all supplied by catabolic fat, then only 278 grams of fat would need to be consumed (2500 ÷ 90).

Only 1,944 grams of catabolic fat would be needed in 7 days, which is about lean 2 kilograms.

This is clearly not factually correct.

Even taking into account the simultaneous consumption of fat, protein, and stored glycogen at this stage, the latter two being less energy dense, if you follow the 1:1 ratio of fat to protein (glycogen), you can only consume 1 kilogram of fat and 2 kilograms of protein (and glycogen) in 7 days, for a total of 3 kilograms of **** consumption, or 3 kilograms of weight loss (fattening).

This is still below the actual weight loss, not to mention, the actual consumption of protein is much lower than this assumption.

This is because there is a process of adaptive change in the body's energy expenditure after fasting, which involves a variety of complex mechanisms and energy "wastage. energy.

In the beginning, the body first consumes stored liver glycogen and muscle glycogen; as glycogen is consumed, glucose is generated from proteolipids and lipids (gluconeogenesis), stimulated by glucagon secreted by the pancreas.

Although glycogen stores are only consumed for about 4-6 hours, due to the replenishment of the gluconeogenic pathway, glycogen is not fully consumed until 24 hours.

Thereafter, energy expenditure is largely dependent on gluconeogenesis and lipolysis, with the major energy consumers, skeletal muscle and cardiac muscle, directly utilizing lipolysis products.

Therefore, protein breakdown for gluconeogenesis is actually very limited, about 70 grams per day, and can only supply 280 kcal.

This means that 2,200 kcal of energy per day comes from lipolysis, which requires the breakdown of at least about 250 grams of fat.

Still, 320 grams of protein and fat consumption is far less than the amount of actual weight loss.

This is because, in the early stages of energy conversion, the body does not utilize the products of fat breakdown (ketone bodies) very well, and a large proportion of the ketone bodies are not efficiently utilized and can only be excreted through the kidneys.

As we know, ketone bodies are organic acids that exist as anions in the body, and kidney excretion of these anions requires the matching of an equal number of moles of cations, which is sodium.

And to excrete these anions, you also need to match an equal amount of water.

Thus, during the first 2 weeks of fasting, and especially the first 1 week, a very large portion of the sodium and water in the body is excreted with the ketone bodies.

This means that not only is a good portion of the energy in the form of ketone bodies wasted, but at the same time, it also causes the body to become somewhat dehydrated.

This results in a much greater weight loss than is required for energy consumption alone.

In fact, there are scientific records of weight changes over 40 days of fasting, not just 1 week:

Roughly speaking, on the first day of fasting, the weight loss was close to 1 kilogram, due to dehydration; on the second day, it dropped rapidly to about 700 grams, and on the seventh day, it went down to about 500 grams, or 1 city pound.

In this way, one week of fasting can result in a weight loss of about 7 to 10 city pounds.

By 2 weeks, energy expenditure is almost entirely dependent on efficient fat utilization, and weight loss can stabilize at 0.3 kg per day.

Therefore, not to mention fasting for 7 days, it is fasting for 40 days, or even longer, the amount of weight loss is well documented.

The reasoning is simple: most of the weight loss during the first week of fasting comes from dehydration due to ketone body excretion;

after resumption of eating, the change in body weight is the inverse of this process, i.e., the amount of body fluids is rapidly restored, leading to a rapid rebound in weight.

In the face of the rapid "rebound" of weight after resumption of eating, many people who do not pretend to understand have made a big fuss about the unreliability of fasting for weight loss.

In fact, it is not scientific to rely on prolonged fasting to lose weight, and it may result in a lack of nutrients other than energy.

However, this does not mean that fasting is not an effective way to lose weight, and that it is easier to bounce back after resuming eating.

Because, fasting fast loss of the original is not "fat", but water; back to eating fast "rebound" is not "fat", the same is water.