No, your metabolism does not slow down in adulthood, new study finds

Researchers have found that metabolic rate stays steady between the ages of 20 and 60, contrary to popular belief

A new study has found that metabolism peaks in childhood, but remains steady in adulthood. Johnny Cohen / Unsplash

The notion that it becomes harder to shift weight as you age has been touted as gospel for decades. But a new study has debunked those claims, showing that metabolism stays steady between the ages of 20 and 60.

The study, published on Thursday in the journal Science, looked at data taken from 6,421 participants over a period of 40 years, to see how factors including size, gender and age affected metabolism.

More than 80 researchers from different labs studied the data, which was gathered using a technique called “doubly labelled water tests”, to see how much carbon dioxide a person produces, which helps to gauge energy expenditure.

The method involves participants drinking water in which some of the hydrogen and oxygen are replaced with isotopes of these elements, which can then be traced in urine samples.

Participants came from 29 different countries, and were aged from eight days to 95 years.

The findings showed that while age does play a role in how fast people burn calories, it doesn’t have as much of an impact on metabolism as previously thought.

“Metabolic rate is really stable all through adult life, 20 to 60 years old,” study author Herman Pontzer, an associate professor of evolutionary anthropology at Duke University in the US, told NBC News. “There's no effect of menopause that we can see, for example. And, you know, people will say, 'Well when I hit 30 years old, my metabolism fell apart.' We don't see any evidence for that, actually.”

The researchers found that total daily energy expenditure and “basal expenditure” – the energy needed to carry out fundamental metabolic functions such as breathing – rose with body size.

Taking this into account, they concluded that infants up to one month old used about the same total amount of energy per day as adults, but at about one year of age, this rose rapidly to about 50 per cent higher than adults.

However, after that age, researchers found that total daily energy expenditure declines slowly through childhood and adolescence at a rate of about -2.8 per cent, until adult levels are reached at the age of 20.

From the age of 20, researchers found that total daily energy expenditure plateaus until about the age of 60, when it then starts to decline once more.

Factors including pregnancy and menopause had no effect on metabolic rate, the study concluded.

Researchers concluded that children are likely to be more active than adults, leading to a higher metabolism. However, teenagers, despite stereotypes of them eating more during their “growing years”, did not have significantly higher metabolic rates than adults.

“Previously there was a suggestion that metabolism might slow in your 30s and that was then thought to [cause] susceptibility to middle-age spread,” another of the study’s authors, Professor John Speakman from the University of Aberdeen in the UK, told The Guardian. “We found no evidence to support that. So if you are piling the weight [on] and your waistline is expanding during your 30s and 40s, it’s probably because you are eating more food, then expending less energy.”