Age and weight gain: scientists debunk popular myths about metabolism

Many have heard that after the age of 20, the metabolism slows down, so people begin to gain weight year after year. Also, we all believe that women have a slower metabolism than men. This is why it is more difficult for them to control their weight. Menopause only aggravates the situation by further slowing down the metabolism in women. As it turned out, all this is not true. The publication told about the new study with the BBC.

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According to a new analysis of the body's energy use, the results of which are that a slower metabolism over the course of a lifetime is completely unrelated to age.

A study of 6400 people aged eight days to 95 years in 29 countries shows that a person's metabolism does not change throughout middle age.

It peaks at the age of one year, remains stable from 20 to 60 years, and then declines.

These discoveries force us to take a fresh look at our understanding of human physiology. The results of the study are likely to change them, and may also have implications in medicine, for example, in determining appropriate doses of drugs for children and the elderly.

The four phases of metabolism

Metabolism is a chemical process necessary to maintain the functioning of the body.

And the larger the size of this organism, be it huge biceps or an excessive supply of fat on the belly, the more energy it needs.

Therefore, the researchers adjusted their measurements for body size to compare the metabolism of people of different sizes and builds.

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Researchers have managed to identify four phases of metabolism in life:

• from birth to one year, when the metabolism changes from the level of the child's mother to the maximum throughout life - 50% higher than in adults;
• slight slowdown by age 20, without any spikes during puberty, about 3% per year;
• unchanged between the ages of 20 and 60;
• a constant decline, with an annual decline of about 0,7%, which by the age of 90 reduces metabolism by 26% compared to average age.

Moreover, this classification works for almost the entire population, of course there are some individual differences.

Some have metabolic rates 25% below average for their age, while others have a quarter higher than expected. But these marginal values ​​do not change the general idea.

“This is a picture we've never seen before and it's full of surprises,” says one of the researchers, Professor John Speakman from the University of Aberdeen. “What surprised me the most was that there is no change in adulthood: if you get crap in middle age, you can no longer blame it on your metabolic decline.”

Childhood malnutrition

It turned out to be curious that the researchers failed to find it.

There was no metabolic surge during puberty or pregnancy, and there was no slowdown during menopause.

The high metabolism in the early years of life also underlines how important this moment is for development and why the consequences of childhood malnutrition can stay with you for life.

“When people talk about metabolism, they mean diet and exercise, but it's really about how your body works, how your cells work,” said Professor Herman Pontzer of Duke University. “At one year of age they are incredibly busy, and when we see a decline with age, we see the cells stop working.”

One of the most surprising findings from this study was the metabolism of babies.

Scientists expected that the newborn baby would have a sky-high metabolic rate - because, as biologists know, small animals burn calories faster than larger ones.

However, it turned out that during the first month of life, babies have the same metabolic rate as their mothers. But soon after the baby is born, he says, something works, and the metabolic rate rises sharply.

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The scientists also expected that they would find a slower metabolism in adults in their 40s, or, in women, when they reach menopause. But, as Dr. Pontzer said, the study authors simply did not observe this.

Human metabolism was measured using so-called double-labeled water, made up of heavier isotopes of hydrogen and oxygen atoms. Scientists measured the number of calories burned by tracking the amount of carbon dioxide exhaled by the participants during their daily activities.

But this water is very expensive, so it took researchers from 29 countries a collaborative effort to collect data on 6400 participants in the experiment.

Dosage of drugs

Such research is very important for medicine.

Professor Ponzer believes that this may help to identify the dependence of the spread of cancer on changes in metabolism and the need to adjust the dose of drugs at different stages.

Among other things, scientists plan to study whether drugs that alter metabolism can slow the progression of diseases in old age.

Rosalyn Anderson and Timothy Rhodes of the University of Wisconsin said that this study has already led to important new discoveries in the field of human metabolism, and it cannot be considered an accident that senile diseases appear and develop just at the moment when the metabolic rate falls.

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Around age 60, no matter how young people look, they change dramatically. “There is a myth about eternal youth,” Anderson says. “But biology objects.” Around age 60, things start to change. There comes a point when everything is no longer the same as it was before.”

Obesity epidemic

Professor Tom Sanders, from King's College London, said: "Interestingly, we found very little difference in total energy expenditure between young and middle age - the time when most adults in developed countries gained weight. "These findings support the view that the obesity epidemic is caused by excess food consumption rather than a reduction in human energy expenditure."

According to Dr. Samuel Klein, director of the Center for Human Nutrition at Washington University School of Medicine in St. Louis, the energy needs of the heart, liver, kidneys, and brain require 65% of total resting metabolic rate, although they account for only 5% of body weight.

A slowdown in metabolism after age 60, he said, could mean that organs begin to function less well with age, which may be the reason why chronic diseases are more common in older people.

He is convinced: "I do not think that it is possible to draw any new clinical conclusions for individuals." When it comes to weight gain, he says, the problem remains the same: people consume more calories than they burn.

In general, Klein said, for public health, as well as understanding diet and nutrition, the results of the study are currently of limited value, since they provide a "bird's eye view of energy metabolism."

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