Can you summon the secret of “not gaining weight” by gathering 150 “chosen” thin people?

Hu Sumei, a lecturer at Beijing University of Technology, once spent two years searching for a type of person in the crowd - the legendary person who "can never gain weight no matter how much he eats."

"In the long run, I can tell whether a person meets our standards just by looking at him or her," Hu Sumei told China Science Daily. She was looking for volunteers who met the requirements for a six-year study, and finding people took up one-third of the time.

"Usually, our impression of this group of people is that they can eat whatever they want and not gain weight. This is because we believe that they will consume excess energy through high levels of physical exercise," said Zhang Xueying, a postdoctoral fellow at the Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences (hereinafter referred to as Shenzhen Advanced Institute).

Their mentor, the famous physiologist John Roger Speakman, attended an academic exchange meeting in 2007. The speaker said: "Studying obese people will only tell us how to become obese. If we want to lose weight, we should study those who are really thin."

He thought this was an interesting idea, so when he came to work in China in 2011, he included this plan to study "thin people" in his application.

Today, 11 years later, Speakman's team published their first research results on the thin population in Cell Metabolism. The conclusions they drew from the data overturned people's understanding of this population.

Focusing on obesity research, frequent "heartbreaking" papers

Speakman is a foreign member of the Chinese Academy of Sciences, a foreign member of the U.S. Academy of Sciences, a fellow of the Royal Society of London, and a member of the European Academy of Sciences. He is one of the few "triple-country academicians" from China, the United Kingdom, and the United States.

He is currently the chief scientist of the Energy Metabolism and Reproduction Research Center of the Shenzhen Institute of Advanced Medicine and a professor of the School of Pharmacy of Shenzhen University of Technology. Speakman has been committed to the research of animal and human energy metabolism for many years.

In recent years, his team has continued to produce results in the field of obesity research and has published a series of research results that have become popular and trending.

On August 13, 2021, Speakman's team published a paper in Science, pointing out that middle-aged obesity can no longer be explained by "decreased metabolic rate". Two weeks later, they published another article in Current Biology, telling everyone: The fatter the person, the less likely it is to lose weight through exercise.

In just half a month, they have stabbed fat friends in the heart twice. So is the result of this study on thin people still so "heartbreaking"?

Rare thin person

It is easy to find a thin person, but it is quite difficult to find a healthy thin person with a BMI (body mass index) less than 18.5 and between the ages of 20 and 40.

According to the US national survey data, the proportion of extremely thin people is about 1.5% to 2%, proving that this group of people is very rare. However, there is currently a lack of relevant data in China, which also brings difficulties to research.

An important task for Hu Sumei, co-first author of the paper, in the early stages of the research was to recruit volunteers for the thin group, but there were very few people who met the experimental requirements.

So much so that later, whether walking in the cafeteria, square, subway, classroom... Hu Sumei was "looking" for volunteers almost anytime and anywhere: "Hello, I see you are very thin, can we study you?" "Want to know why you are so thin? Do you want to take a test?"

What is more challenging is that these volunteers must not only be thin enough, but also healthy enough. The researchers first excluded people who were obese, pregnant, breastfeeding, or thin due to various diseases, and further investigated their diet and exercise status through questionnaires.

Finally, they recruited 150 qualified "healthy thin people". Interestingly, among these 150 people, 83% were women. In contrast, the proportion of women in the normal weight group (21.5 < BMI < 25) was only 46.8%.

"We expected that the ratio of men to women would be similar, but we didn't expect this to happen," Hu Sumei said. "We are not sure about the specific reasons, but I think that on the one hand, women are more willing to participate in such research because they are more concerned about their body shape and diet. On the other hand, women may account for a larger proportion of healthy super-thin people."

In the process of interacting with volunteers, Hu Sumei found that most of the super-thin people hope to gain some weight. Many of them complain that they "can eat a lot, but just can't gain weight." But is this really the case?

Imaginary thin people VS real thin people

After completing the recruitment of volunteers, the researchers tested them on eight indicators: height and weight, body composition, blood biochemical indicators, endothelial function, lung function, basal metabolic rate, activity level and total energy expenditure (double-labeled water method).

The so-called "doubly labeled water method" is to have volunteers drink doubly labeled water, then collect the volunteers' urine for 14 consecutive days, and analyze the changes in the abundance values ​​of markers in the urine to measure the volunteers' energy consumption.

This is also the "gold standard" for measuring daily energy expenditure in a free-moving state.

After calculation, the researchers found that the "healthy thin" group consumed 12% less energy through diet than the normal weight group. This result has already excluded those who deliberately diet to stay slim.

What is unexpected is that the amount of exercise these thin people do is not high at all, and is even 23% lower than that of the general population.

Although these people did not eat much and moved even less, their resting metabolic rate was unexpectedly higher than expected. "This is very different from our initial assumption, or even the opposite," said Zhang Xueying, co-first author of the paper, to China Science Daily.

Like many people, Zhang Xueying also knows some friends who claim that they can never gain weight no matter how much they eat.

Whether from an intuitive perspective or from a scientific hypothesis, researchers initially thought that the reason these people were thin was because they ate a lot, consumed more energy, and controlled their weight through a lot of exercise.

"It now seems that even if there are such people, they are a very small minority among thin people. After all, none of our 150 volunteers fit this pattern," said Zhang Xueying.

Zhang Xueying also said that the biggest regret of this article is that it only measured the food intake of thin people from the perspective of energy, but did not investigate what they ate specifically or ask about their feeling of fullness.

"Incorporating these types of information in future studies may help us discover more interesting information," she said.

Is being thin a "genetic lottery"?

In modern society where thinness is generally considered beautiful, people often say that those who are naturally prone to thinness have "won the genetic lottery."

This may be true. Compared with normal-weight people, these thin people have better heart health markers - such as low-density lipoprotein cholesterol and blood pressure.

"We often emphasize the benefits of exercise for health, but it seems that, in terms of maintaining physical health, a lower body fat percentage seems to be more important than exercise itself," said Zhang Xueying.

In short, these healthy thin people can maintain a higher basal metabolic rate (possibly related to thyroid hormone levels) and better physiological and biochemical indicators without controlling their diet or doing extra exercise. What kind of genetic genes have created them?

"Our preliminary genetic studies pointed out that there are single nucleotide polymorphisms in some genes of these individuals. We have tried to knock out these genes in mice and found that it can cause corresponding phenotypic changes." Speakman, the corresponding author of the paper, told China Science Daily, "In the next stage of research, we will pay more attention to the genetic mechanisms behind these phenotypes."

Related paper information:

https://doi.org/10.1016/j.cmet.2022.05.012

Source: China Science Daily (2022-07-18 Page 1 News)

Text｜China Science Daily reporter Li Chenyang and Diao Wenhui