Like to spend your time sitting on the couch all night watching TV? Or spend most of your day in front of a computer? Certainly not a good habit or lifestyle. Scientists have recently discovered that the body's daily activities - such as standing and walking - largely determine how fat or thin a person is. For those who weigh more than is healthy, this means that there are other ways for people to control their weight besides physical activity. However, this is not a panacea, as some people seem to be naturally more accustomed to being stationary than others.
The couch potato experiment
Endocrinologist James Levien of Mayo Medical Center in Minnesota, USA, led the experiment. The purpose of the experiment was to find out just how important the energy expended by the body's daily activities is in the overall balance of energy intake and expended by the body.
Six years ago, Levien's group first introduced a concept of daily energy expenditure -- non-exercise energy expenditure, or NEAT -- which refers to the amount of energy expended by the body's movements in daily life, including energy expended sitting in a chair and energy expended while standing, walking, and talking. Energy. By definition, deliberate exercise, such as the energy expended playing basketball, running and jumping rope, is not NEAT.
Levin's group enlisted 20 volunteers, 10 of whom were lean, while the other 10 were moderately obese. The volunteers all worked at Mayo Medical Center, and all called themselves "couch potatoes" -- a word that, in English, means people who don't want to move and prefer to be still, such as spending a lot of time sitting on the couch watching TV.
While none of the volunteers were very physically active, their obesity levels fell into two distinct categories. What caused the difference in weight they appeared to have? Levine's research group decided to compare how their NEAT differed. One of the tricks was to dress these volunteers in special underwear. These undergarments were actually a set of instruments that recorded body movement and posture (sitting, standing and walking) and included sensors and computers. And this motion-monitoring technology was earlier used in the control of fighter jets.
Every half a second, the underwear recorded the volunteer's movement. The volunteers wore the underwear almost 24 hours a day. Each morning, they come to Levine's lab to be weighed and receive a new set of underwear. Then the scientists downloaded the previous day's volunteer's exercise data from the old underwear's computer. At the same time, the scientists gave the volunteers calorie-determined diets -- the volunteers weren't allowed to eat privately during the experiment because that would cause the scientists to be unsure of how many calories the volunteers actually consumed in a day.
After 10 consecutive days of testing, the scientists found differences in the behavior of the two groups of volunteers, who were both fat and thin. On average, the fatter "couch potatoes" sat in their chairs for 150 minutes more per day than the thinner ones. Apparently, sitting in a chair uses much less energy than standing. Because the caloric intake of the couch potatoes was tightly controlled by the scientists during the experiment, "our study shows that the amount of energy expended in people's daily activities is far more important in obesity than we previously thought," Levine said. In addition, they found that if fat "couch potatoes" performed their daily activities as well as thin ones, they would burn 350 kilocalories of energy per day (about 1.47 million joules, which could power a 60-watt lamp for nearly seven hours), and they could lose 15 kilograms of fat in a year. The findings were published in the Jan. 28 issue of the journal Science.
The problem with skimping
People are often under the impression that if they don't get a lot of physical activity and eat a lot of high-fat, high-calorie foods (often called "junk food"), they will gain weight. It is true that if you run 30 kilometers every day, you will not get fat. But this somewhat extreme approach to weight control is unrealistic: most people don't have the time to exercise every day, or the space to do so.
And running a lot of miles every day -- perhaps 10 kilometers of exercise on foot is an astronomical number compared with people living in cities today -- or eating very little food is exactly how our ancestors lived tens of thousands of years ago. Humans back then had a tougher life than modern people in order to hunt animals and gather plants for food. They had no supermarkets or fast food restaurants. Sugar, salt, and condiments like tomato sauce were luxuries in the Stone Age. This early life of "poverty" created a special preference for these foods. When the availability of these foods ceased to be a problem, people inevitably ate more of them.
It's a short history for humans to be entitled to feel that fat is bad for their health
In the 1960s, Prof. James Neel of the University of Michigan came up with an intriguing theory: that there are genes in us (inherited from our ancestors, of course) that make us very miserly in our management of our energy balance - in other words, the human body tends to put a lot of energy into our bodies whenever possible, and that's why we're so hard on ourselves. possible, the body tends to store energy in the form of fat. For our cave-dwelling, half-starved ancestors, having such a "strategic reserve" of energy was a clear survival advantage.
Since World War II, agricultural production has increased dramatically. In the developed countries of Europe and the United States, food is cheap and readily available. With the exception of sub-Saharan Africa, in many developing countries, having enough to eat is no longer a rarity. But mankind's evolved "frugal" nature persists. For example, obesity has become an epidemic in the United States over the past few decades. According to a 2000 survey, about 64 percent of Americans are overweight or obese by medical standards.
Obesity isn't just a cosmetic problem; it can lead to a long list of diseases, including high blood pressure, heart disease, diabetes and stroke, to name a few. The U.S. spends tens of billions of dollars each year to lose weight or treat obesity-related diseases.
Still nature
But the solution to obesity can't be found in a simple "eat less" admonition. In fact, scientists still don't fully understand the main causes of the obesity epidemic in modern society. With the abundance of food in supply and a decrease in human activity, which factor is more important to the obesity epidemic? For example, in the UK in the 1980s, the number of people who were obese doubled, despite a fall in average energy intake. "This suggests that modern inactive lifestyles are at least as important as dietary factors as far as the etiology of obesity is concerned," comments Eric Ravussin of the Purington Biomedical Research Center in the same issue of Science.
The human body needs to eat food for energy, just as airplanes need fuel to fly. Each day, 50 to 70 percent of the energy we get from food is used to maintain basic body functions, such as oxygen acquisition and transportation and cellular metabolism. This share of energy is roughly constant. In addition, the body uses a portion of its energy to maintain body temperature. Of course, because humans use warm clothing, this portion of energy is only about 10 percent.
The remaining 20 to 40 percent of energy consumption is an indeterminate expenditure. It includes planned physical activity, as well as non-physical activity energy expenditure, or NEAT, as studied by Levine.If the body takes in the same amount of energy as it expends each day, then a person's body weight remains essentially the same. However, if there is a small energy surplus, say tens of kilocalories of energy, every day, then after a year the body may have gained a few extra kilograms of fat.
NEAT: Non-exercise energy expenditure is fundamental to weight loss
Levin's study showed that fat "couch potatoes" burned 350 kilocalories of energy less per day than thin ones. So if their weight changed, would they maintain their exercise habits? Levine's team conducted further experiments. They adjusted the weight of the "couch potatoes" over a two-month period, reducing the energy intake of the fat ones by 1,000 kcal per day and increasing that of the thin ones by 1,000 kcal per day. After two months, the two groups of "couch potatoes" gained and lost several kilograms each. The scientists then followed their activities for 10 days. It turned out that they did not change their exercise habits. The fatter group was not more willing to sit down because of the weight gain, while the thinner group was not more willing to stand up and move around because of the weight loss. This suggests that the activity habits of these people were biologically determined.
Levin argues that this certainty of activity habits likely reflects different brain chemistry differences that may ultimately be controlled by certain genes. Those genes may make people more inclined to jump up and down or sit quietly on the couch. "This provides circumstantial evidence that NEAT is genetically determined," Ravussin says.
But the fact that NEAT is dependent on genetics also poses a problem. If a person is naturally more inclined to be sedentary, that is, to have a lower NEAT, then a way to achieve weight control by altering that nature seems less realistic. But Levine is optimistic about starting a "NEAT revolution": "It's totally feasible, because we don't need special equipment or a big field to do this kind of (daily) exercise. Compared to running a marathon, (increasing) NEAT is something everyone can do." Perhaps the first step to weight control is to throw away the TV remote from the couch.