Study suggests metabolism declines after age 60 years
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Metabolic rates appeared to be highest during infancy and stable through adulthood before declining after age 60 years, according to findings published in Science.
Also, researchers found that energy expenditure rate patterns did not differ between men and women of similar body and muscle size.
“As we age, there are a lot of physiological changes that occur in the phases of our life such as during puberty and in menopause. What’s odd is that the timing of our ‘metabolic life stages’ doesn’t appear to match the markers we associate with growing up and getting older,” Jennifer Rood, PhD, associate executive director for cores and resources at Pennington Biomedical Research Center, said in a press release.
Rood and colleagues analyzed the effects of age, body composition and sex on total daily energy expenditure using a large, diverse database of 6,421 individuals (64% female) in 29 countries who were aged 8 days to 85 years. The researchers calculated total expenditure using doubly labeled water measurements and basal expenditure with indirect calorimetry.
The doubly labeled water measurements were collected through a urine test, according to the press release. For the test, participants drank water in which the hydrogen and oxygen were replaced with “naturally occurring heavy forms,” the release said. Then the researchers measured how quickly the molecules were flushed out.
Infancy phase
The researchers said they uncovered four “distinct” phases of adjusted total and basal expenditures in a lifetime. The first phase occurred in infancy.
During the first month of life, energy expenditure was similar to that of adults, with adjusted total expenditure of 99% (± 17.2%) and adjusted basal expenditure of 78.1% (± 15.0%). The measurements increased rapidly during the first year, with a break point at about 0.7 years old. Between 9 and 15 months of age, adjusted total and basal expenditures were about 50% more than that of adults, according to the researchers.
“Some people think of their teens and 20s as the age when their calorie-burning potential hits its peak. But the study shows that, pound for pound, infants had the highest metabolic rates of all,” study coauthor Peter Katzmarzyk, PhD, associate executive director for Population and Public Health Sciences, said in the release.
Juvenile phase
The juvenile expenditure phase lasted throughout childhood and adolescence, during which total and basal expenditure and fat-free mass continued to increase, the researchers reported. However, size-adjusted expenditures steadily declined, with adjusted total expenditures declining at a rate of 2.8% (±0.1%) per year from 147.8% (± 22.6%) for those aged 1 to 2 years, to 102.7% (± 18.1%) for those aged 20 to 25 years. The break point in adjusted total expenditure occurred around 20.5 years, then plateaued.
The researchers reported that puberty during 10 to 15 years of age did not increase adjusted expenditure. Regression models revealed that boys and men aged 1 to 20 years had a higher total expenditure and adjusted total expenditure than girls and women, but sex overall did not significantly impact the rate of decline in total expenditure with age.
Adulthood phase
The third phase of expenditure occurred in adults aged 20 to 60 years, during which total and basal expenditure and fat-free mass were “remarkably stable,” even during and after pregnancy, the researchers wrote. The break point occurred at 63 years (95% CI, 60.1-65.9), which marked the beginning of total expenditure decline.
Older adulthood phase
The fourth and final phase of adjusted total and basal expenditure occurred in adults aged older than 60 years, according to the researchers. Total expenditure declined at about 0.7% each year (±0.1%). For participants aged 90 years or older, total expenditure was about 26% lower than that of middle-aged adults, Rood and colleagues found. The data suggest that a person aged 90 years or older requires 26% fewer calories than a middle-aged adult, according to the release.
The findings “shed light on human development and aging and should help shape nutrition and health strategies across the life span,” Rood and colleagues wrote.
In a related perspective, Timothy W. Rhoads, an assistant scientist in the department of medicine at the University of Wisconsin-Madison, and Rozalyn M. Anderson, PhD, a faculty member of the Geriatric Research, Education and Clinical Center at the William S. Middleton Memorial Veterans Hospital in Wisconsin, wrote that expenditure decline from age 60 years, the same timeframe that the increase in incidence of noncommunicable diseases and disorders begins, “cannot be a coincidence.”
“The findings indicate that life stage needs to be carefully considered when choosing disease models. This is particularly important for research on the etiology of age-associated diseases and disorders,” they wrote.
References:
EurekAlert! Metabolism changes with age, just not when you might think. https://www.eurekalert.org/news-releases/925132. Accessed August 13, 2021.
Pontzer H, et al. Science. 2021;doi:10.1126/science.abe5017.
Rhoads T, Anderson RM. Science. 2021;doi:10.1126/science.abj9797.
Perspective
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Fatima Cody Stanford, MD, MPH, MPA, MBA, FAAP, FACP, FAHA, FAMWA, FTOS
Our gradual reduction in energy expenditure over the course of life speaks volumes to the need for us to maintain a robust active lifestyle, even as we age. We know that our muscle mass declines over the age of 60, and we should make efforts to be as active as possible for as long as we are able. When muscles are not utilized, we develop sarcopenia, which portends even lesser energy expenditure. As such, I do recommend that all persons regardless of their age work to ensure that they’re getting in regular activity. I think it is key to find the activity that suits you and continue it throughout the course of your lifetime. It will allow for greater mobility as we age.
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