https://www.nytimes.com/2021/08/12/health/metabolism-weight-aging.html

As We Grow Up Does Our Metabolism Slow Down?

New research challenges what we believe about how our bodies burn calories.

“It’s literally the running total of how busy your cells are throughout the day.”

Associate professor of evolutionary anthropology Herman Pontzer, Duke University, principal investigator for this new study on metabolism. Pontzer says the study shows what we assume about our metabolism (when it slows down, speeds up, differences between genders) is just plain wrong: "I’m in my 40s; I feel different than I did in my 20s — I buy it, too. All that intuition was never backed up by data. It just seemed so sure.”

Researchers used previously-collected data from nearly 6,500 people ranging from 8 days old to 95 years old. 

They measured calories burned per day and adjusted for body size and amount of muscle/fat present.

 After controlling for variables, this study found no significant difference exists between men's and women's metabolic rates, and it appears metabolic changes fall into four phases.

Newborns begin with a similar metabolism as adults but at about 1 month old, it suddenly shoots way ahead - with a metabolic rate 50% faster than adults.

From ages 1 to 20, metabolism gradually declines each year. 

From around age 20 to 60, metabolism stabilizes & remains level (even during pregnancy & menopause). 

Around age 60, metabolism begins decreasing in the following years.

“It’s really important not only for basic science but because metabolism — how we utilize energy in our body — is absolutely central to any understanding of disease or well-being.”

Professor Richard Bribiescas, Yale University. Researchers say understanding metabolism will provide insight into aging, disease, obesity and the way we care for or treat chronic disease.

The majority of the time, our body is metabolizing what we ingest to simply stay alive - some estimates say that accounts for 50 - 70% of what we metabolize. Why does it seem like we gain weight as we get older?  Researchers say the explanation "your metabolism slows down" doesn't appear to be the primary driver and this research may ignite a deeper dive into a constellation of factors from genetics, to hormones, muscle mass and diet.

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NYT: The New Science on How We Burn Calories

NYT: What We Think We Know About Metabolism May Be Wrong

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Emily Hooker