What we think we know about metabolism may be wrong

Everyone knows the traditional knowledge about metabolism: people put pounds every year from their twenties, especially in middle age, because their metabolism slows down. Women are slower to metabolize than men. That’s why they struggle to control their weight. Menopause only exacerbates the situation and further slows down women’s metabolism.

According to all wrong A paper published in Science on Thursday.. Using data from about 6,500 people between the ages of 8 and 95, researchers found that there were four different periods of life as far as metabolism was concerned. They also found that after controlling other factors, there was no real difference between male and female metabolic rates.

Findings from research have the potential to reshape the science of human physiology and may affect some medical practices, such as determining the appropriate drug dose for children and the elderly.

“It will appear in textbooks,” predicted Lian Redman, an energy balance physiologist at the Pennington Institute for Biomedical Sciences in Baton Rouge, Louisiana, calling it a “very important treatise.”

Rosalin Anderson, a professor of medicine at the University of Wisconsin-Madison and studying aging, wrote: Outlook Accompany the paper. In an interview, she said the discovery was “blown away.” “We need to fix some of our ideas,” she added.

However, the study shows a “30,000-foot view of energy metabolism,” so the impact of the findings on public health, diet, and nutrition is currently limited. Human Nutrition Center, Washington University School of Medicine, St. Louis. “I don’t think you can make a new clinical statement,” he added, for the individual. When it comes to weight gain, the problem remains the same. People eat more calories than they burn.

Metabolic studies are expensive, so most published studies have few participants. However, Herman Pontzer, an evolutionary anthropologist at Duke University, who is the lead researcher for the new study, said the project’s participating researchers agreed to share their data. There are more than 80 co-authors in this study. Combined with efforts from half a dozen laboratories collected over 40 years, they had enough information to ask general questions about lifelong metabolic changes.

All research centers involved in the project were studying metabolic rates in a way that was considered the gold standard — double-labeled water. It involves measuring calories burned by tracking the amount of carbon dioxide that a person exhales during daily activities.

The researchers also knew the height and weight of the participants, as well as their body fat percentage, and were able to determine their basal metabolic rate. Of course, smaller people burn less calories than larger ones, but when correcting for size and fat percentage, the group asked, were their metabolisms different?

“It was really clear that we weren’t dealing well with how body size affects metabolism, or how aging affects metabolism,” Dr. Pontzer said. rice field. “These are the basic basics that seem to have been answered 100 years ago.”

At the heart of their discovery was that metabolism was different in all people across four different stages of life.

• By the age of one, when calorie burning peaks, it is infancy and accelerates to 50% above the proportion of adults.

• Then, from the age of 1 to about 20, metabolism gradually slows down by about 3 percent per year.

• From 20 to 60 years old, it’s stable.

• And after the age of 60, it decreases by about 0.7% per year.

When researchers controlled body size and people’s muscle mass, there was no difference between men and women.

As expected, metabolic rate patterns apply to the population, but vary from individual to individual. Some have a metabolic rate 25% lower than the average age, while others are 25% higher than expected. However, these outliers do not change the general pattern and are reflected in the graph showing the trajectory of metabolic rate over the years.

The four periods of metabolic life depicted in the new treatise show that “energy consumption per pound is not constant.” Prices vary depending on age. It goes against the long-standing assumptions she and others in nutrition have made.

Individuals with lifelong metabolic trajectories and outliers open many research questions. For example, what are the characteristics of people with higher or lower metabolism than expected, and is there a relationship with obesity?

One of the most surprising discoveries to Dr. Pontzer was the metabolism of infants. He expected, for example, that the metabolic rate of newborns would be very high. After all, the general rule of biology is that small animals burn calories faster than large animals.

Instead, Dr. Pontzer said that during the first month of life, babies have the same metabolic rate as their mothers. But shortly after the baby was born, he said, “something starts and the metabolic rate goes up.”

The group also predicted that metabolism would begin to slow down in the 40s of adults, or in the case of women, when menopause begins.

But Dr. Pontzer said, “We didn’t see it.”

A slowdown in metabolism that begins around the age of 60 results in a 20 percent reduction in metabolic rate by the age of 95.

Dr. Klein says he gains an average of over a pound and a half in adulthood, but it is no longer believed to be due to poor metabolism.

According to Dr. Klein, the energy requirements of the heart, liver, kidneys and brain account for 65% of the resting metabolic rate, but only 5% of body weight. He added that slow metabolism after age 60 may mean that important organs are failing with age. There may be one reason why chronic illnesses tend to occur most often in the elderly.

Even college students may see the effects of metabolic shifts around the age of 20, Dr. Klein said. “When they graduate from college, they burn less calories than they did when they started.”

And around the age of 60, no matter how young people you see, they are changing in a fundamental way.

“There is a myth of staying young,” said Dr. Anderson. “That’s not what biology says. Around the age of 60, things start to change.”

“There are times when things are gone as before.”