New Study Reveals Unexpected Findings About Aging and Metabolism

A new study from a team of international researchers finds that our metabolism does not slow down over the span of a lifetime as traditionally believed, but rather stalls from age 20 to 60. 

“We can see that infants have accelerated metabolism, and that not until our 60s is there a cellular slowing down in metabolic rate,” said a researcher of the study Lara Dugas, associate professor at Loyola University Chicago. 

The study, which examines the total daily energy expenditure of the human body, which reflects daily energy needs, shows that metabolism peaks around age 1, then declines roughly 3% per year until around age 20. 

From there, the study shows that metabolism plateaus until about age 60, when it starts to slowly decline again, by less than 1% annually.

“This is tightly regulated by growth, and energy demands of infancy, growing brains and organs, and then the slowing down to the adult level,” said Dugas. 

Dugas said our metabolism declines at age 60 because we have less cellular repair as we age, and therefore this slows down our metabolic rates.

To conduct the study, researchers used a database called the IAEA DLW Database Consortium, consisting of over 6,500 individual data points from studies conducted from 1981 to present day, allowing them to explore questions around energy expenditure and metabolism by boosting the sample size.

Researchers reviewed the outcomes of what is called the doubly labeled water method in 6,400 people in 29 countries ages 8 to 95. 

Dugas said that doubly labeled water utilizes stable isotopes, essentially a special labeling of oxygen and hydrogen molecules, to make them appear different to our own body’s water content. 

“When you drink a glass of doubly labeled water, the water mixes with your own body water, and is excreted from your body proportionally to your metabolic rate,” said Dugas.

Dugas said that a faster metabolic rate will make the special oxygen and hydrogen molecules appear faster in our urine, and slower metabolic rate will mean that these molecules appear at a slower rate.

Researchers also disproved traditional assumptions that metabolic rates spike during periods of pregnancy, puberty, or menopause, which were not found in the study to have any impact on metabolism.

“We assumed that growing bodies, whether teenage bodies or pregnancy, had higher energy demands, over and above what could be expected. Instead, it’s proportional to the adjusted body mass,” said Dugas.

The study might also offer new insight into the critical importance of healthy infant nutrition on metabolism later in life.

“We have always known that malnourishment during [the] infancy period probably results in stunting, and an increased risk for some non-communicable diseases like obesity and type 2 diabetes,” Dugas said. “It is not that [a properly nourished individual has a] faster metabolism, it means that you have a normal metabolism, because you got the correct amount of calories for your metabolic rate. On the other hand, if you were malnourished, you may have a ‘slower’ metabolism,” continued Dugas.

Based on these findings, Dugas said the study could have major implications for obesity and type 2 diabetes research. However, she also said that the study does not address energy intake, which is the primary driver of the obesity epidemic.