— Topics —
Genetic factors vs environmental factors


Does Obesity Run in the Family or Is It Due to the Living Environment?


  1. What was the relationship of weight between adoptees and adoptive parents?
  2. What was the weight of the twins raised apart?
  3. What do we consider a change in environment?: My thoughts
  4. Will the shape of your body from childhood continue?
    The bottom line

Is obesity inherited from parents?

Let us recall our classmates in elementary school. To some extent, we can imagine, if not one hundred percent, that if the parents are thin, their children are often thin, and if the parents are fat, their children are often fat.

The question here is whether this is due to genetics or due to the living environment. Here is one such study I’d like to introduce.

a family

1. What was the relationship of weight between adoptees and adoptive parents?

"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 obesogensFor these reasons, many consider the current environment the major cause of obesity.

environmental factors for obesity

Conventional calorie-based theories of obesity place the blame squarely on this “toxic" environment that encourages eating and discourages physical exertion. Dietary and lifestyle habits have changed considerably since the 1970s (e.g. car, television, computer, fast food, high-calorie food, sugar, etc.).

Therefore, most modern theories of obesity discount the importance of genetic factors, believing instead that consumption of excess calories leads to obesity. Eating and moving are voluntary behaviors, after all, with little genetic input.

So-exactly how much of a role does genetics play in human obesity?"
(Jason Fung. The Obesity Code. Greystone Books, 2016, Page 21-2.)

"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.

adoptive families

Studying a sample of 540 Danish adult adoptees, Dr. Stunkard compared them to both their adoptive and biological parents. 

If environmental factors were most important, then adoptees should resemble their adoptive parents. If genetic factors were most important, the adoptees should resemble their biological parents.

No relationship whatsoever was discovered between the weight of the adoptive parents and the adoptees.(*snip*)

Comparing adoptees to their biological parents yielded a considerably different result. Here there was a strong, consistent correlation between their weights.

The biological parents had very little or nothing to do with raising these children, or teaching them nutritional values or attitudes toward exercise. Yet the tendency toward obesity followed them like ducklings. When you took a child away from obese parents and placed them into a "thin" household, the child still became obese.(*snip*)

This finding was a considerable shock. Standard calorie-based theories blame environmental factors and human behaviors for obesity. Environmental cues such as dietary habits, fast food, junk food, candy intake, lack of exercise, number of cars, and lack of playgrounds and organized sports are believed crucial in the development of obesity. But they play virtually no role."
(Fung. The Obesity Code. Pages 22-3.)

2. What was the weight of the twins raised apart?

"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*)

a dentical twin

However, it is immediately clear that inheritance cannot be the sole factor leading to the obesity epidemic.

The incidence of obesity has been relatively stable through the decades. Most of the obesity epidemic materialized within a single generation. Our genes have not changed in that time span.

How can we explain this seeming contradiction?"
(Fung. The Obesity Code. Pages 23-4.)

3. What do we consider a change in environment? : My thoughts

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.

Even those who were slim in their youth may gain five or ten kilos in a short period of time at a certain age, triggered by something (living alone, marriage, parenting, stress from work, etc.). Some people put on weight every time they try dieting to lose weight.

In other words, many of us, in our hearts, have probably noticed that changes in eating habits or our living environment can change our body shape.

■What is the "change in environment" that causes a change in weight here?

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.

set-point weight

On the contrary, I believe that a fundamental increase in weight and body shape occurs when one’s set-point weight itself goes up, which is induced by intestinal starvation.
And since at least three (+one) factors are required to induce intestinal starvation, living with adoptive parents alone does not necessarily alter one’s set-point weight.

[Related article] 

Three (+one) Factors to Accelerate “Intestinal Starvation”

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.

4. Will the shape of your body from childhood continue?

childhood obesity

One thing to note here is that the body shape in childhood (say, around three to five years old) tends to continue into adulthood.

When I think back to my classmates in first and second grade, the girls and boys who were fat (although they were not big eaters) often have a similar body shape even decades later.

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.


The bottom line

(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) O
f 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.



Why Does the Body Perceive That It Is More Starved than in the Past?


  1. How has our Japanese diet changed over the past fifty years?
  2. The Pima tribe who gained weight under rations, not prosperity 
  3. The newer the diet in history, the less fit the body is
<End Note>

1.How has our Japanese diet changed over the past fifty years?

I was born in 1970, about fifty years ago. That was when twenty-five years had passed since the end of the World WarⅡ, and Japan was in the midst of its rapid economic growth.

In retrospect, I feel that the food scene was quite different from what it is today. My parents were farmers in the country side of Osaka, growing rice and mushrooms. We also had about twenty chickens to get fresh eggs.

On the dining table in the morning, there was usually rice, miso soup, pickles, traditional stewed vegetables, and half-dried fish. I remember the family eating together.
Of course, we sometimes ate bread, but my father did physical labor, so rice was an essential part of breakfast.

Balanced breakfast

(Typical Japanese breakfast we used to have)

■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.

fast food

Even in the 1970s, school lunches already had bread as their side dish rather than rice (apparently at the behest of GHQ, which ruled after the war), and those of us who had grown accustomed to such a diet began to prefer bread, noodles, and other wheat products even as adults.

Along with this, we liked to eat meat and processed foods rather than fish with bones. We began to prefer soft foods to fibrous and hard foods, and the traditional vegetable stews that had been commonly eaten became less and less common.

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.

Obesity rate in Japan

(Percentage of adults with a BMI of 25 or higher: In both men and women, it has been increasing since 1980 

One might think that increased caloric intake was the cause of being overweight.

However, on a caloric basis, the average daily caloric intake of the population in 1970 was twenty-two-hundred kcal, yet in 2010 it had decreased to eighteen-hundred-fifty kcal. [1] 

light breakfast and lunch

(an inverted triangle-type diet)

To explain this in my theory, the modern diet is often low in fiber and heavy on easily digestible carbohydrates and meat, which can, in turn, induce intestinal starvation based on how we combine the foods.

In particular, the following eating patterns can easily create a state in which all food is digested in the gut.

(1) Two meals a day, leaning toward carbohydrates and easily digestible protein.

(2) A simple, light meal for breakfast and lunch, and added fibrous vegetables and nutritional foods at dinner. (What I call an inverted triangle-type diet).

2. The Pima tribe who gained weight under rations, not prosperity

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. 

Pima tribe

By the 1870s, the Pima were living through what they called the “years of famine.”(*snip*) The tribe was still raising what crops it could but was now relying on government rations for day-to-day sustenance.(*snip*)

What makes this observation so remarkable is that the Pima, at the time, had just gone from being among the most affluent Native American tribes to among the poorest.
Whatever made the Pima fat, prosperity and rising incomes had nothing to do with it; rather, the opposite seemed to be the case.

And if the government rations were simply excessive, making the famines a thing of the past, then why would the Pima get fat on the abundant rations and not on the abundant food they'd had prior to the famines? Perhaps the answer lies in the type of food being consumed, a question of quality rather than quantity.(*snip*)

So maybe the culprit was the type of food. The Pima were already eating everything “that enters into the dietary of the white man,” as Hrdlička said. This might have been key. 

The Pima diet in 1900 had characteristics very similar to the diets many of us are eating a century later, but not in quantity, in quality."
(Gary Taubes. Why We Get Fat. New York: Anchor Books, 2011, Pages 19-23.)


[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 meat, 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.

3. The newer the diet in history, the less fit the body is

"The idea is that the longer a particular type of food has been part of the human diet, the more beneficial and less harmful it probably is— the better adapted we become to that food.

And if some food is new to human diets, or new in large quantities, it's likely that we haven't yet had time to adapt, and so it's doing us harm. (*snip*)

Wild boar meat

The obvious question is, what are the “conditions to which presumably we are genetically adapted”? As it turns out, what Donaldson assumed in 1919 is still the conventional wisdom today: our genes were effectively shaped by the two and a half million years during which our ancestors lived as hunters and gatherers prior to the introduction of agriculture twelve thousand years ago."
(Taubes. Why We Get Fat. Pages 163-4.)

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. 

The food we used to eat

If the state of "no food" (starvation) was recognized when all food was digested in the entire intestinal tract, then during the hunting-and-gathering age and farming age when people ate wild boar meat, nuts, root vegetables, and unrefined grains, etc., their intestines would not have been in a state of complete starvation even if they couldn’t eat anything for a whole day (because of the long intestines).

In contrast, a modern diet high in refined wheat/rice, starch, easily digestible protein, and processed foods can lead to intestinal starvation even in just 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.

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

End Note

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.