When people reach middle age, many people have the same question: when they are not young, they eat more and their consciousness increases. Why are they getting fatter?
　　
       We can rely on factors such as staying up late, sedentary lifestyle, stressful, and irregular diet, but recently scientists have claimed that they have found the cause of middle-aged well-being. A paper published in the well-known journal Nature Medicine mentioned that as people age, fat turnover will decrease dramatically, and according to the mechanism discovered by the research, there may be ways to save the well-being of middle-aged people. What is going on?

　　1. "Bad" white fat determines fatness

　　People always like to joke that some middle-aged people are "greasy", and the first thing is to get rich. In fact, there are indeed many middle-aged people who cannot get rid of this "standard configuration". It is common to accidentally gain weight.

　　In order to study the "fat" of middle-aged people, a research team led by Professor Kirsti Spalding of the Caroline Medical School in Sweden conducted a 16-year study of 54 volunteers and followed them for an average of 13 years. It was found that the important reason for the well-being of middle-aged people is that the lipid turnover capacity (ability to store and remove lipids) of human fat cells is reduced, especially the rate of lipid consumption is greatly reduced. Young people are also prone to getting blessed, with an average weight gain of 20%.

　　At the same time, the well-being of middle-aged people has an important relationship with the "bad" white fat in the human body. The important component of white fat cells is the "triglyceride" that we often see on blood test sheets. Its storage and consumption (turnover) ability often determines whether people are fat, normal, or thin.

　2. The longer the fat accumulation, the harder it is to clear

　　There are many studies on human obesity, but what makes this study special is that it is creative.
　　First, the Spalding team selected the body part that best represents fat turnover, that is, the subcutaneous fat tissue in the abdomen. In addition to facilitating the acquisition of fat, the fat in this part is more sensitive to changes in lipid turnover and therefore more able to reflect lipid turnover. status.
　　Second, measuring fat turnover requires an easy-to-measure indicator, and researchers chose carbon 14.
　　Carbon 14 is a radioactive isotope of carbon and was first discovered in 1940. Since carbon is also an element of organic matter, paleontologists can infer the age of its existence based on the remaining carbon 14 components in the body of the dead organism.

　　The researchers chose carbon 14 as a measure of fat turnover, which is also related to this. Researchers say that animals and plants in nature absorb carbon 14, and when people eat these animals and plants, carbon 14 enters the body. Carbon 14 is usually deposited in triglycerides in the human body. The higher the carbon 14 content, the higher the unmetabolized fat deposited. Therefore, researchers used carbon 14 to measure the level of body fat.

　　Of course, the relationship between carbon 14 and human fat content has complicated mathematical formulas to calculate, which is difficult for non-professionals to understand. But the basic principle is that by assessing the level of carbon 14 penetration in lipids, the level of lipid turnover can be assessed proportionally. People with low lipid turnover are obese, otherwise they are normal or thin.

　　Without this creative research, there would be no further progress. After the specific plan was drawn up, researchers recruited volunteers from 2001 to 2003 and divided them into two groups. The first group had an average age of 38 years, a total of 54 people, 44 women and 10 men, and the follow-up period ranged from 7 to 16 years, with an average of 13 years; the second group had an average age of 43 years, all women, with a total of 44 people, and they had undergone bariatric surgery and were followed up for 4 to 7 years, with an average of 5 years.
　　During the study and follow-up, researchers regularly collected subcutaneous fat from the abdomen of volunteers, recording their living and eating habits, and changes in their various physical indicators. By performing a complicated calculation of the average lipid age (the age of lipids in white adipose tissue, determined by measuring the concentration of carbon 14 in triglycerides) and the rate of lipid removal, several results were obtained.

　　First, the older the average lipid age, the lower the lipid removal rate. In other words, the longer the fat accumulates in the body, the more difficult it is to remove it, and the accumulation of fat is the basis of overweight and obesity.

　　Second, the average age of the first group of volunteers during the 13 years of follow-up increased by 0.6 ± 0.8 years, indicating that their lipid removal rate was decreasing. At the same time, volunteers gained an average of 20% in weight even if they did n’t eat much (maintaining the food they used to eat when they were young) and increased exercise. For example, when he was young, he weighed 70 kilograms, and now it is 84 kilograms. These increases are redundant lipids.

　　The results of the second group of 44 female volunteers who had undergone bariatric surgery were also comparable to the first group of volunteers. This further proves that people who are middle-aged can hardly remove body fat.

　　3. Why Lipid Turnover Is Decreasing

　　Although middle-aged obesity is associated with a decline in lipid turnover, research by Spalding's team still supports previous findings that reducing food intake can alleviate the decline in lipid turnover (avoid obesity), and increasing exercise also reduces weight. helpful. The main point is to hold your mouth and open your legs, but because many people either can't control their mouths or can't open their legs, it is difficult to achieve the goal of losing weight.

　　However, this novel study does not fully understand why people's lipid turnover capacity declines to middle age. One inferable mechanism is that after a person reaches middle age, the body's metabolic capacity declines, lipid turnover capacity also declines, and fat storage exceeds consumption, and people become fat.

　　The results of another study published recently in the International Journal of Epidemiology are even worse for middle-aged people. Studies suggest that if you are overweight or obese before the age of 40, your risk of cancer will increase, with a 70% increase in endometrial cancer risk, a 58% increase in male renal cell carcinoma risk, and a 29% increase in male colon cancer risk. All cancers, including men and women, have a 15% increased risk. The study followed the volunteers for 18 years and the results were more reliable.

　　4. It is possible that fat becomes "good"

　　So how can a middle-aged person who is blessed save themselves? In fact, we can find a way out from the root of obesity and find a breakthrough point from brown fat.
　　The reason why the white fat mentioned above is bad fat is because its function is mainly to store fat, and less to burn fat for energy. The reason why brown fat is good is because it can be burned for energy. Brown adipocytes contain a large number of mitochondria (where the fat is burned for energy), and the brown adipose tissue is rich in capillaries, so it appears tan.

　　Brown fat decreases in adulthood and is mainly distributed on the sides of the neck, on the back, near the collarbone and around the spine. Its heat-producing ability is very strong. If a small piece of brown fat is activated, it can quickly consume glucose and fat to generate a lot of calories. In particular, when the fat stored in brown fat itself is exhausted, it will also capture white fat from other parts of the body as its new fuel.

　　Therefore, as long as it can promote brown fat burning, it is possible to lose weight. One way is to put people in a cold environment. In this case, people will use two rapid heat production methods to maintain body temperature. One is shivering heat production, which is snoring, which provides heat through the contraction of skeletal muscles; the other is non-shivering heat production, also known as metabolic heat production, which is mainly generated by the burning of brown adipose tissue.

　　Some researchers have experimented with this. After placing obesity-prone mice at 5 ° C for 1 week, mice lost an average of 14% of their body weight. Experiments on humans also have certain effects. Controlling the temperature to feel colder, but not cold enough to tremble, the density of brown fat in the human body will increase, and metabolism will be more active. However, this method may not work for the entire population, because the proportion of obese people living in cold regions is not small, and people will unknowingly ingest more food in colder conditions, and may be more likely to gain weight .
　　Moreover, another study pointed out that 7.5% of women and 3% of men did not detect active brown fat in colder environments. There may be two reasons: they have a certain percentage of brown fat in their bodies but cannot be activated to burn; their brown fat is inherently less.
　　For the case that brown fat cannot be activated for burning, some researchers believe that a switch to activate brown fat can be found to promote fat burning. This switch may be succinic acid. Succinic acid is a metabolic product that promotes fat burning. Tests on mice have found that when mice are allowed to drink water containing succinic acid for 4 weeks, they will not gain weight even if they consume high-fat foods. However, for various reasons, no human trial has been conducted in this study so far.

　　For people born with less brown fat, turning white fat into brown fat that is easy to burn is also a good way to lose weight. Researchers have discovered a hormone called irisin that promotes the conversion of white fat to brown fat. Previous research has found that brown fat also originates from white fat and can be converted through exercise. Now researchers have finally figured out the key: human muscles secrete a protein called PGC-1α after exercise, which promotes the formation of irisin, which is then acted on white fat cells and induced to turn brown. Fat cells.

　　It is conceivable that middle-aged people who do not want to exercise can promote the conversion of white fat to brown fat by introducing the method of irisin. The specific method is to inject an adenovirus containing the irisin gene into the body, so that this gene can be expressed and function. Tests in mice proved that the weight did indeed decrease after receiving the injection, and no toxicities or adverse reactions were detected. However, being safe for mice is not necessarily safe for humans. Due to concerns about the safety of adenovirus as a gene-carrying vector, this method has not been tested in humans so far, and of course it has not been officially used. In the future, if you can use drugs to promote the conversion of white fat to brown fat, it should be a healthy way to lose weight. (Zhang Tiankan)