If you haven’t read these articles below, please read them first.

A Set-Point Weight; The Precondition Regarding the Rebound Effect

Two Meanings to the Phrase 'Gaining Weight'

In my previous article, "Two meanings to the phrase 'gaining weight' ," I wrote that your set-point weight increases by the hunger mechanism－strictly speaking, intestinal starvation. I would like to explain it simply.

(1) It happens when you eat and when your gastrointestinal tract is working.

(2) It refers to the situation between meals, such as between breakfast and dinner, or lunch and late dinner, or dinner and the next lunch, where every substance in the entire intestines from a range of seven to eight meters has been digested.(It might be small intestine only.)

In other words, the stomach and intestines are working to nourish the body, but all the food eaten has been digested, and the body perceives it as “there is no food.” It’s different from simple hunger in that:

 (a) basically, everything, including protein, fat, and even water, is digested;

 (b) there is no fiber or anything close to it (※This is why it is said refined carbohydrates make you fat).

However, in this era with an abundance of food, it seems like those who eat a lot are obese and those that don't eat much are thin, and this tends to lead to a misunderstanding.

There is a reason for this, and  it is my own theory based on my personal experience.
The question here is : "In what way do our bodies perceive starvation ?" Starvation is not decided by the amount of how much we’ve eaten, but rather, how the digestion process in the intestines proceeds.

That is to say, even if you eat a lot, if your diet is skewed toward easily digestible carbohydrates and some protein, and you end up being very hungry for hours, you will be close to a starvation situation.

On the other hand, even if you eat a little, if you eat a well-balanced diet including vegetables, dairy, meat, and fat  every five to seven hours, then your body won’t perceive you as being in starvation mode. When there are some undigested substances in your intestines, your body perceives them as "there is still food." In other words, your intestines decide everything.
  

Please check out my blog below before reading this one.

→ A Set-Point Weight; The Precondition Regarding the Rebound Effect

I would like to define this term first. There are two meanings of the expression "gaining weight" which we use daily. I think the confusion of these meanings causes a lot of misunderstandings.

For example,  “you'll gain weight if you eat a lot of calories” or "despite dieting and eating less, you gain even more weight when you rebound,” etc.

I realized this when I got really thin, but I think the confusion of these two meanings results in various misunderstandings and false information, and most people are dieting in the wrong way.
    

The first one is “gaining weight” meaning to go back to your set-point weight based on the mechanism of maintaining your present condition. 

▷Toru Watanabe, a Japanese actor, used to be heavy, but with a diet, he weighed around 70kg when he appeared on a television show.

However, when he got married at twenty-six, he couldn't maintain his diet anymore and ate a lot and he went back to 130kg. (It is said that he made a new record for his weight change every time he dieted.)

On the other hand, the second “gaining weight” expression means that your set-point weight itself increases.
Though I have reduced the amount of my food intake, I shattered my previous weight level and gained three kilograms in the last year which means I’ve gained ten kilograms in the last three years... meaning my maximum weight has increased.  
 

For example, someone who has never been more than sixty kilograms has become sixty-three kilograms in the last year. In this case, it means that his/her set-point weight itself increased from sixty to sixty-three kilograms.

When you gain weight to your set-point weight from a rebound after a diet, it's the (A) mechanism, but if you gain weight naturally more than your set-point weight, it is the (B) mechanism. This is because a calorie-restricted diet can create a situation of intestinal starvation.

It is generally believed in Japan that eating when your metabolism is slowing down makes you gain more weight, but it has already been proven that fat people have a higher basal metabolism[1].
     

■Japanese Sumo wrestlers are famous for eating a lot of rice and being fat, but I believe that, to put it in extreme terms, they will gain weight because of a mix of (A) and (B).

Although it looks like they eat more and are gaining weight, the mechanism should be the same as that of people who try dieting, but in the end, they gain more weight than before due to the rebound effect.
       

References：
[1] Dr. Jason Fung, The Obesity Code, 2016, Pages 62.

First of all, I want to explain the most important point. It's the assumption that each person has the ability to maintain their present condition, also known as preserving current stasis in the body.
I recognize that this is the precondition of everyone regarding weight control.

However, despite the lack of official proof or definition, some researchers have already used the concepts of 'set-point weight.' Additionally, my "base weight" can be confused with "baseline weight," which is used in some studies. Therefore, I will use 'set-point weight' or ‘set-point’ for body weight going forward."

     
In this example, Person A's set-point weight is forty-eight kilograms. However, for Persons B and C, the weights they quickly revert to when they let their guard down and eat a lot—sixty kilograms and eighty-seven kilograms, respectively—can be considered their actual set-point weight. This means that their homeostatic functions are working to maintain those weights. 

So, it’s difficult to assume a person’s body and weight condition only with caloric intake.

Consider the example above, that if A continues an intake of 100kcal over her recommended daily caloric intake every day for several months or years, the assumption is that it will accumulate into fat and she will eventually gain weight up to the eighty-kilogram level. This is wrong (She might gain weight but that is a different mechanism).

In general, people who are overweight are more likely to be restricting calories and eating modestly, so their current weight is often lower than their set-point weight. On the other hand, thin people don't have caloric restrictions, so their current weight and their set-point weight are often close. (Temporary overeating may lead to further weight gain beyond the body’s set-point, but I believe this weight gain is temporary and does not alter one’s set- point weight.）

Therefore, ‘thin A’ won't gain weight even if she eats a lot, and B and C will gain weight immediately as soon as they eat a lot.           

But, as soon as the match was over and he started to eat, his weight increased ten kilograms in a few days. The rate of going back to his set-point weight was fast. Those who have tried diets and eat less than usual might have experienced this. Often, it's called the rebound effect.