Let me explain something about the core of this blog.
Perhaps for most of you it is hard to believe me, but I’ll just write the facts as they are, as I experienced them. I did not write this from my imagination, but based it on my own analysis of what actually happened to me.

When I got into college, my total body weight fell down to the thirty-kilo range, so I knew exactly why I gained almost five kilos so rapidly in a few days, even though I didn’t eat much.

The idea of storing fat in the body as a reserve against starvation is something every researcher considers at one time or another.

However, it is said that this theory is an idea that has been rejected by researchers throughout history. This is because many overweight people often eat more, and many African refugees are thin and malnourished. 

One might say, “If starvation makes us fat, then African refugees would be obese.”

In contrast, many of us in developed countries are more likely to eat westernized foods made from wheat, meat, eggs, etc., which provide good nutrition and are easier to digest. Therefore, if we focus on the inner workings of our intestines, we are more prone to inducing intestinal starvation.

The reality is that being overweight has become a problem even among the poor populations in the world. The common denominator there is not an excessive intake of calories or carbohydrates (sugar), but a poor balance of food (cheap carbohydrates, lack of nutritious food including vegetables, etc.).

In my blog, I mentioned that one’s base weight value goes up by inducing intestinal starvation, and I want to explain what it means here. For the sake of explanation, I will use plants as an example.

The same goes for humans, and just eating a lot of calories doesn’t necessarily mean we all gain weight and become overweight. Even if we eat only one meal a day, as long as it’s well-balanced, there will be enough nutrition left in the intestines to be absorbed.

(2)Using an example of a plant, weight gain by inducing intestinal starvation and an increase in base weight could be explained in the same way as a plant that is extending its roots and taking in more nutrients. (See figure below)

Actually the villi (folds) of the intestines do not grow, but the absolute level of absorption goes up by expanding the surface area over which nutrients can be absorbed(*1).
(I will explain this in greater detail to the researchers.) 

So even if you eat the same amount of food as you did before, you will gain weight instantly. (For some, it might be three kilos in a year, for others, it might be ten kilos in just a few days.)

This, I believe, is the fundamental difference between obese and thin/lean people. 

(*1)The small intestine is said to have a surface area of more than a tennis court when all its folds(villi) are spread out. This is because it absorbs more nutrients. 

When your base weight goes up and you gain weight, it means that the balancing point, in terms of "energy- in, energy-out," has gone up, which can generate a more positive energy cycle and make it more difficult to lose weight.

When dieting, temporarily reducing the caloric intake to lose weight means reducing the "fertilizer" in the example of a plant. However, it is only a temporary weight loss, and you will likely return to your original weight when you start eating a normal diet again (the rebound effect).

Moreover, the reason why each time some people diet, they rebound and gain more weight than before is that skipping meals or eating light meals (not enough vegetables) can lead to intestinal starvation, which can further increase your base weight.
     

It is not that after you get fat, you gain muscle to support it. I believe that muscle is built at the same time you gained weight, at least up to a certain weight, because overall nutritional intake, including protein, has increased.

The increased intake of nutrients as a whole, including protein, creates a positive cycle of energy, which leads to the following phenomena. Digestive enzymes, hormones, etc. are also made from proteins (amino acids), which may increase the ability to digest food and increase the appetite. So, it is no wonder that people with larger bodies or stronger stomachs generally eat more than others.

There exists a cause-and-effect reversal phenomenon: people do not gain weight because they eat more, but because the bigger they are, the  hungrier they become, and in turn, they eat more.
    

On the other hand, if a lean person eats balanced meals three times a day, every day, he or she doesn’t induce intestinal starvation. And there is a good chance they will stay the same weight and have the same appearance for the rest of their life, regardless of caloric intake.

Therefore, "fatness" and "non-fatness," in this regard, are not obesity genes. 

Also, for people like me who are very thin, being thin itself can reduce the amount of protein and other nutrients that can be taken in, thus a negative energy cycle continues. In turn, the muscles that support the stomach and intestines become weak and droopy, and the ability to digest food is also diminished by not secreting enough digestive enzymes.

This is a vicious circle where thin people can’t gain weight and remain thin.