In Japan, the image of sumo wrestlers in particular may lead to the image that "eating more makes you fat," but I would like to explain that this is the same mechanism as "those who end up rebounding after dieting and gain more weight than before" or "those who gradually gain weight by skipping breakfast or having a late dinner.”

First of all, I'm going to illustrate how both of them gain weight in the figure below. 
  

When you see big eaters in a food eating competition, some may ask, "Why don't they get fat even though they eat so much?” But, from my theory, it is not at all surprising.

It’s not that they have a special "non-fattening constitution," but that anyone who eats like that from morning to night is less likely to gain weight (although I wonder why they can eat so much food at once).

Please understand that the way of eating of a sumo wrestler is a far cry from that of an eating competitor.
   

(1)A wrestler must weigh at least sixty-seven kilograms to be admitted. People who are overweight or muscular from the beginning tend to have stronger stomachs, and are thought to have a relatively high digestive rate. Such people are more likely to induce gut starvation than thin people.

(4)They traditionally eat two meals a day: the first meal is around eleven a.m. after morning practice, and dinner is around six p.m.
Since they practice from the early morning without breakfast, if dinner is finished at seven p.m., it means that they do not eat for about fifteen to sixteen hours until the next meal. It make sense to do intense morning training on an empty stomach to gain weight.

Of course, there are some wrestlers who try to eat snacks or supplements late at night in order to take in more calories, but my idea is that it makes easier to gain weight when they don't eat.

(1)Sumo wrestlers are famous for being big and fat, but they do not gain weight because their daily caloric intake exceeds their daily caloric expenditure.
Their traditional diet and exercise makes sense in terms of weight gain in that it facilitates the creation of intestinal starvation.

(2)Intestinal starvation is more likely to be induced when a person who has a big body from the start eats relatively easily digestible foods with lots of carbohydrates (rice) and two meals a day.

(3)The mechanism by which wrestlers gain weight is the same as that of "people who diet and gain more weight than before due to the rebound effect.”
In the case of sumo wrestlers, since they eat a lot every day, this happens almost simultaneously, and they appear to eat a lot and gain weight.
    

According to a survey, more than fifty percent of Japanese people put on some weight during the period of staying at home by government order to prevent the spread of the coronavirus.

I think two classic examples of "eating a lot or stopping exercising makes you fat" fit here.
Normally, these people were under the strain of their jobs, moving all day long, eating in moderation, and paying attention to caloric intake. If that tension is gone and they simply exercise less and eat more, they will naturally gain weight.

Sometimes I hear people say, "I ate too much at the all-you-can-eat buffet yesterday and gained three kilograms in one night.” They may have simply gained body fat or the weight of the food in their gut may also be a factor.

But It is a big mistake to say, "Okay, let's skip today's lunch." 

With the recent gourmet food boom, many delicious foods are introduced on television and social media, while many people are worried about gaining weight and are trying to eat less.

If you skip meals or eat light meals (e.g. hamburgers and coffee) to reduce calorie and carbohydrate intake, you will deal with hunger for a longer period of time.

Even if you lose a little weight temporarily, the lack of fats/oils, dairy products, and fibrous vegetables can lead to intestinal starvation and an increase in your set-point weight over the long haul.

Unknowingly, your set-point weight may go up, and one day, when you eat like you used to, you may find that you have reached your highest weight ever. And it will be harder to lose weight than before.

The first step in becoming leaner is to eat three well-balanced meals religiously every day. 
Even if you want to reduce total caloric and carbohydrate intake, be sure to consume a variety of foods from a diverse group of foods.
   　　　

(1) Some people claim to have gained a few kilos during the Covid self-quarantine period, but I believe most cases can be explained by a return to one’s set-point weight as well as a rebound effect after dieting.

(2) The idea of adjusting for yesterday's excess calories by eating fewer calories today is a mistake when it comes to maintaining a stable weight in the long run.

(3) People who usually eat less and hold back on the foods they want to eat for dieting, and occasionally splurge on treats, are more likely to gain weight over the long haul.
Irregular eating, where a person eats on and off, can cause intestinal starvation when dealing with hunger over many hours, unknowingly increasing their set-point weight.

(4) Since the gastrointestinal tract basically begins with breakfast and the food we eat reaches the rectum in around twenty hours or so (it differs from person to person), it is important to eat three well-balanced meals every day if you do not want to gain weight.
           

"Obese children often have obese siblings. Obese children become obese adults. Obese adults go on to have obese children. Childhood obesity is associated with a 200 percent to 400 percent increased risk of adult obesity. This is an undeniable fact. (*snip*)

Families share genetic characteristics that may lead to obesity. However, obesity has become rampant only since the 1970s. Our genes could not have changed within such a short time. Genetics can explain much of the inter-individual risk of obesity, but not why entire populations become obese.

Nonetheless, families live in the same environment, eat similar foods at similar times and have similar attitudes. Families often share cars, live in the same physical space and will be exposed to the same chemicals that may cause obesity–so-called chemical obesogens. For these reasons, many consider the current environment the major cause of obesity.

"The classic method for determining the relative impact of genetic versus environmental factors is to study adoptive families, thereby removing genetics from the equation.(*snip*)

Dr. Albert J. Stunkard performed some of the classic genetic studies of obesity. Data about biological parents is often incomplete, confidential and not easily accessible by researchers. Fortunately, Denmark has maintained a relatively complete registry of adoptions, with information on both sets of parents.

"Studying identical twins raised apart is another classic strategy to distinguish environmental and genetic factors. Identical twins share identical genetic material, and fraternal twins share 25 percent of their genes. 

In 1991, Dr. Stunkard examined sets of fraternal and identical twins in both conditions of being reared apart and reared together. Comparison of their weights would determine the effect of the different environments.

The results sent a shockwave through the obesity-research community. Approximately 70 percent of the variance in obesity is familial.(*snip*)

I think this is a very interesting study because it compared data from biological parents and adoptive parents.

However, can we assert from the results of this one alone that the influence of genetics was much greater and environmental factors were much less significant?

I believe, as Doctor Fung mentions, the rapid increase in obesity in recent years (since about 1970) has much to do with changes in our living environment (what we eat, irregular lifestyle,etc.),not the genes.

The study considers a child living with adoptive parents or twins raised separately to be a "change in living environment," but I think there is a problem with this study.

If a family can afford to take in a child as adoptive parents, don't they have some money to spare and feed their adoptee a somewhat balanced diet three times a day?
Although what they eat and caloric intake may differ from family to family,  those changes are not necessarily "environmental changes" that cause changes in weight. Just because the adoptive parents are thin does not mean that adoptees will become thin even if they eat the same diet.

In Japan over the past few decades, our traditional eating habits have been declining.  Instead, Westernized eating and diverse work styles have become more prevalent.
Amid these changes, intestinal starvation is more likely to be induced when unbalanced diets (high in easily digestible carbohydrates and ultra-processed foods, and with a lack of vegetables, etc.) combines with irregular lifestyle habits (skipping breakfast, eating late at night, etc.).

This is what I would like to call the "environmental factors and human behaviors" for the recent obesity epidemic, and while genetic factors are, of course, undeniable, I believe that environmental factors are quite significant.
           

From my theory, that means that their set-point weight has not changed, and in this study, if there are no environmental factors that cause changes in their set-point for body weight, then wouldn't the body shape from childhood basically continue?

But, I’m simply wondering what the childhood body shape is due to? Whether it is genetic factors or the way food is prepared during childhood－including weaning－is a question that remains unanswered.

(1) In a study regarding adoptive families and examining how genetic and environmental factors influence being overweight, no correlation was found between the weight of adoptive parents and that of their adoptees. On the other hand, when the adoptees were compared to their biological parents, there was a consistent correlation between the weight of both.

A study of twins raised separately also concluded that "genetic influences are far more significant.”

(2) Many researchers had previously blamed "environmental factors and individual behavior” for the recent obesity epidemic, but this study concluded that genetics had far more impact than environmental factors.

However, I find this study problematic. The fact of children living with adoptive parents or twins raised separately is not necessarily an environmental factor that causes changes in weight.

(3) Of course, I do not think we can ignore the genetic factor, but I believe that the recent obesity epidemic is caused by a combination of what we eat－westernized diets, refined carbohydrates, processed foods, etc.－plus lifestyle changes. 

A major change in weight and body shape occurs when one’s set-point weight goes up, which is induced by intestinal starvation.

(4) If there is no significant change in one's set-point weight, I think the body shape from childhood is expected to continue. However, I 'm uncertain what determines childhood body shape, whether it is heredity or the way food is prepared during childhood, including weaning.
         

■The 1970s, when the dining scene changed dramatically

I think it was after 1970 that our dining landscape slowly changed. I had not been taken to restaurants much when I was a kid, but fast food restaurants and other restaurant chains opened one after another in all corners of Japan, and many people began to eat Western food.

McDonald's (since 1971), Kentucky Fried Chicken (since 1970) and family restaurants called Skylark (since 1970) were the most famous among them. In 1974, the first convenience stores (called Seven-Eleven) opened in Tokyo, followed by a rapid increase throughout the country. Instant foods such as cup noodles and frozen foods also increased rapidly, reflecting busy social conditions.

Our lifestyles also changed dramatically. More and more people began to work at desks rather than at physical jobs. Nighttime lifestyles became the norm, and more people didn't even eat breakfast.

It was probably around this time that obesity began to increase in Japan. Nowadays, it is not unusual to see women over one hundred-kilograms on the streets.

As an example of how obesity has increased as old traditional eating habits have declined and became westernized, I would like to cite a Native American tribe known as the Pima, although the situation is slightly different.
This is the second time I quote from Mr. Taubes' "Why We Get Fat," but this part is very important and may be the key to solving the problems of obesity, diabetes, and other diseases.
    

"Consider a Native American tribe in Arizona known as the Pima. Today the Pima may have the highest incidence of obesity and diabetes in the United States. Their plight is often evoked as an example of what happens when a traditional culture runs afoul of the toxic environment of modern America. (*snip*)

Between 1901 and 1905, two anthropologists(Russell and Hrdlička) independently studied the Pima, and both commented on how fat they were, particularly the women. (*snip)

Through the 1850s, the Pima had been extraordinarily successful hunters and farmers. 

     
[Related article] Wealthy Ones Get Fat? Poor Ones Get Fat?

In terms of food, I believe that Japanese people in 1970 were eating a lot of different kinds of food than today. There were no convenience stores, and the diet was based on mom's home cooking, with a variety of seasonal vegetables and fish.

In contrast, the modern diet is based on easily digestible carbohydrates and processed meat products, and the variety of food ingredients we eat seems to have decreased dramatically.

Many people are normally worried about gaining weight and are dieting, and then they occasionally splurge and eat high-calorie food as a reward. The situation is different, but if we focus on the inside of the intestines, I can say that it is the same as what happened to the Pima population.
         

     
I believe what the author tried to get across was that the modern diet of allowing large amounts of carbohydrates is not genetically compatible with our bodies, and that eating meat and its fat may be more compatible and less harmful to us on a genetic level.

I will quote this passage above to explain my intestinal starvation mechanism.

Suppose (and it makes more sense) that God created a genetic blueprint for people to "store body fat" in case they could not find food. 

In contrast, a modern diet high in quickly digested foods —such as refined wheat and rice, starches, processed meat and fish products, and fast food—can, depending on the combination, lead to a state of intestinal starvation in as little as half a day.

I believe it is the entire intestines (or it may be the small intestine only) that makes all the decisions, and it goes to show that inside the gut, many of us are  starving more today than in the past.

References：
[1]Yasuo Kagawa(香川靖雄) , Clock Gene Diet (時計遺伝子ダイエット), 2012, Page 15.

People sometimes say, "Japanese food culture is healthy by world standards," but I believe this to be a relic of the past until around the year 2000 at the latest. Now, I feel that traditional Japanese food culture is dying in the average household.

Children who grew up eating fast food are now in their fifties and sixties, and their children are now in their thirties. Thus, in about fifty to sixty years (about two generations), the opportunity to eat traditional foods will have faded away, and the food culture will change greatly.

And, with the shift in diet, it seems like that diseases such as diabetes, kidney disease, heart disease, cancer, and stroke, which were once not as common, are on the rise, just as they are in the Western countries.
    

First, please refer to the following article. 
The Calorie Principle and Weight Gain; The Causality Has Been Obscure

According to Gary Taubes,  the author of Why We Get Fat (2010), in the early 1900’s, Carl von Noorden, a German diabetes specialist, first argued that we get fat because we take in more calories than we expend.

This view has persisted to the present day, leading many experts to firmly believe that excessive caloric intake and/or lack of exercise are the primary causes of weight gain[1].  This time, I would like to share the “law of thermodynamics,” which was said to be the basis for that theory. Mainly quoted from the book, it is so interesting that I think it is worth reading.
        

Because all mass－our fat tissue, our muscles, our bones, our organs, a planet or star, Oprah Winfrey－is composed of energy, another way to say this is that we can't make something out of nothing or nothing out of something.

This is so simple that the problem with how the experts interpret the law begins to become obvious.

All the first law says is that if something gets more or less massive, then more energy or less energy has to enter it than leave it.

It says nothing about why this happens. It says nothing about cause and effect. It doesn't tell us why anything happens; it only tells us what has to happen if that thing does happen. A logician would say that it contains no causal information.（*snip*)

If you asked me this question, and I said, Well, because more people entered the room than left it, you'd probably think I was being a wise guy or an idiot. Of course more people entered than left, you'd say. That's obvious. But why? And, in fact, saying that a room gets crowded because more people are entering than leaving it is redundant－saying the same thing in two different ways－and so meaningless.

Now, borrowing the logic of the conventional wisdom of obesity, I want to clarify this point. So I say, Listen, those rooms that have more people enter them than leave them will become more crowded. There's no getting around the laws of thermodynamics. You'd still say, Yes, but so what? Or at least I hope you would, because I still haven't given you any causal information. 

This is what happens when thermodynamics is used to conclude that overeating makes us fat. （*snip*)

"The first law states that energy can neither be created nor destroyed. In other words, energy can be converted from one form to another, but the total amount of energy in the universe remains constant. How might this law apply to weight management?

Suppose someone has stable weight over time. The first law dictates that, in theory, the number of calories consumed by this individual in the form of food is equal to the calories the individual expends during metabolism and activity. In other words, 'calories in = calories out’.(*snip*)

However, the first law of thermodynamics actually refers to what are known as ‘closed systems' －ones that can exchange heat and energy with their surroundings, but not matter. Is this true for human beings? 

Two authors have made excellent points about the relationship between thermodynamics and weight management. Based on those thoughts, I would also like to mention two points about the relationship between thermodynamics and my theory.
  

(2) When energy intake increases

Based on my intestinal starvation mechanism concept, even if a person who has maintained the same weight over the years, significantly reduces their usual caloric intake (e.g. about two thousand kcal daily) and the intake of carbohydrates, but meets the "three factors + one" criteria that cause intestinal starvation, they will gain weight (this means that the set-point weight itself has risen due to an increase in absorption ability).

[Related article] →Three (+one) Factors to Accelerate “Intestinal Starvation”

    
Of course, weight gain occurs when you return to your original diet afterward. In this case, since absorption efficiency itself has increased compared to before, both body fat and lean tissue contribute to the weight gain.

In short, even though you are eating the same amount of food (calories) as before, you are taking in more energy and nutrients into your body than before, which means you are getting bigger/fatter. In the words of Taubes, "a room crowded with ten people now has eleven people," and in this case, it is “intestinal starvation” that has caused it.