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Everyone knows the conventional wisdom about metabolism: People gain weight every year starting in their 20s, especially as their metabolism slows down in midlife. Women’s metabolisms are slower than men’s. That’s why they have a hard time controlling their weight. Menopause only makes things worse, it slows women’s metabolisms even more.

All wrong, according to one Article published Thursday in the journal Science. Using data from nearly 6,500 people ranging in age from 8 days to 95 years, the researchers discovered that there are four different life stages based on metabolism. They also found that after controlling for other factors, there was no real difference between the metabolic rates of men and women.

The findings from the research are likely to reshape the science of human physiology and may also have implications for certain medical applications, such as determining appropriate drug doses for children and the elderly.

Leanne Redman, an energy balance physiologist at the Pennington Biomedical Research Institute in Baton Rouge, La., predicted it would “be in the textbooks” and also called it an “important paper.”

Rozalyn Anderson, a professor of medicine at the University of Wisconsin-Madison who studies aging, wrote: a point of view accompanying paper. In an interview, he said he was “blown away” by his findings. “We will have to reconsider some of our ideas,” he added.

But the implications of the findings for public health, diet, and nutrition are currently limited because the study gives “a 30,000-foot view of energy metabolism,” said Dr. Said Samuel Klein. Center for Human Nutrition at Washington University School of Medicine in St. “I don’t think you can make new clinical explanations,” he added, for an individual. When it comes to weight gain, he says, the problem is as always: People take in more calories than they burn.

Metabolic research is expensive and therefore most published studies have very few participants. But the new study’s principal investigator, Herman Pontzer, an evolutionary anthropologist at Duke University, said the researchers involved in the project agreed to share their data. The study has more than 80 co-authors. By combining the efforts of half a dozen laboratories that have gathered over 40 years, they have had enough information to ask general questions about changes in metabolism over the lifetime.

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

The researchers also had participants’ height and weight and body fat percentage, which allowed them to look at baseline metabolic rates. A smaller person will, of course, burn fewer calories than a larger person, but the group corrected for body and fat percentage, asking, “Did their metabolisms differ?” Asked.

Dr. “It was really clear that we didn’t get a good handle on how body size affects metabolism or how aging affects metabolism,” Pontzer said. “These are the basic basic things you thought would have been answered 100 years ago.”

Central to their findings was that metabolism differs for all people at four different stages of life.

• By age 1, there is an infancy when calorie burn is at its peak, accelerating until it reaches 50 percent above the adult rate.

• Then, from age 1 to age 20, metabolism slowly slows to about 3 percent per year.

• It remains constant from age 20 to age 60.

• And after age 60, it declines by about 0.7 percent per year.

After the researchers controlled for body size and the amount of muscle people had, they found no differences between men and women either.

As might be expected, while metabolic rate patterns hold true for the population, individuals differ. Some have metabolic rates 25 percent below the average age, while others have rates 25 percent higher than expected. But these outliers do not change the overall pattern, which is reflected in the graphs showing the trajectory of metabolic rates over the years.

Dr. Redman noted that the four metabolic life cycles shown in the new paper “do not have a constant rate of energy expenditure per pound.” The rate depends on age. This goes against the long-held assumptions of him and others in nutritional science.

Trajectories of metabolism and outliers over a lifetime will open up a host of research questions. For example, what are the characteristics of people whose metabolism is higher or lower than expected, and is it associated with obesity?

Dr. One of the findings that surprised Pontzer most was the metabolism of infants. For example, he expected a newborn baby to have a very high metabolic rate. After all, a general rule in biology is that small animals burn calories faster than large ones.

Instead, Dr. Babies have the same metabolic rate as their mothers during their first month of life, Pontzer said. But shortly after a baby is born, “something kicks in and the metabolic rate goes up,” she said.

The group also expected that adults’ metabolism would start to slow down when they were in their 40s, or at the onset of menopause for women.

However, Dr. “We didn’t see that,” Pontzer said.

The metabolic slowdown that begins around age 60 causes a 20 percent drop in metabolic rate by age 95.

Dr. Klein said that although people gain, on average, more than a pound and a half a year during adulthood, they can no longer attribute this to slowed metabolisms.

Dr. The energy needs of the heart, liver, kidney and brain account for 65 percent of resting metabolic rate, although they only make up 5 percent of body weight, Klein said. A slower metabolism after age 60 may mean important organs work less well as people age. This may be one reason why chronic diseases tend to occur most often in older people.

Dr. Even college students can see the effects of metabolic change around age 20, Klein said. “They burn fewer calories when they finish college than when they started.”

And at around age 60, no matter how young people look, they change fundamentally.

Dr. “There is a myth about youth retention,” Anderson said. “That’s not what biology says. At the age of 60 and around, things start to change.”

“There is a point in time when everything is no longer the same as before.”