Metabolism doesn’t slow down in middle age, shocking new study reveals

Packing on the poundage? Sorry, suckers: We can’t use middle age as our excuse for that spread anymore!

A revelatory new study has determined that metabolism, long thought by most of humankind to decline progressively during adulthood, is actually stabilized between the ages of 20 and 60 — when it actually starts tanking.

An international team of killjoy researchers, whose work was published Friday in the journal Science, discovered that metabolism is at its highest in infants — naturally — who burn calories about 50% faster than adults. That rate declines yearly by about 3% until they reach the age of 20 or so, when metabolism plateaus through middle adulthood. At 60, the slump returns at a depressing rate of about 1% more per year until we drop dead.

What this means: We can no longer blame middle age as the primary reason for amassing newfound weight. For accuracy, researchers accounted for metabolic differences in volunteers, such as body size muscle to fat composition.

“Metabolic rate is really stable all through adult life, 20 to 60 years old,” said study author Herman Pontzer, an associate professor of evolutionary anthropology at Duke University, who spoke to NBC News on Thursday about the research.

Pontzer went on to pontificate about new data that’s likely to send a shiver down the lucrative wellness industry’s collective spine:

“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,” said Pontzer, whose new book, “Burn” (Avery), is about new frontiers in bariatric health.

As part of a global experiment, 6,400 participants, ages 8 days to 95 years, were asked to perform a “doubly labeled water” test, in which some of the hydrogen and oxygen atoms were replaced with their isotopes, making their pathway easily traced through urine samples.

“By calculating how much hydrogen you lose per day, and how much oxygen you lose per day, we can calculate how much carbon dioxide your body produces every day,” Pontzer explained to NBC News. “And that’s a very precise measurement of how many calories you burn every day, because you can’t burn calories without making carbon dioxide.”

The findings, said Pontzer, were a long time coming as scientists now have access to such a large test group.

Pontzer also said, “This was the first time that we had the ability to do this with a really big data set that would allow us to pull apart the effects of body size and age and gender and all these things on our energy expenditures over the day.”

The study is shedding new light on how our cells age, indicating that our metabolism has less to do with physical activity and more with our biology.

“People thought, ‘Well, maybe it’s because you’re less active, or maybe it’s because people tend to lose muscle mass as they get into their 60s, 70s and older,’ ” said Pontzer. “But we can correct for all those things. We can say, ‘No, no, no, it’s more than that.’ It’s that our cells are actually changing.”

However, Dr. David Buchin, director of bariatric surgery at NY’s Northwell-Huntington Hospital, told The Post the new research results “do not make much of a difference for everyday people. There is a morbid obesity problem in our country and people still need to diet, exercise. This study should not make people approach their weight loss any differently, they still need to diet and exercise to maintain weight loss.”

Meanwhile, in an editorial published in tandem with the study, University of Wisconsin geriatrics researchers Timothy Rhoads and Rozalyn Anderson suggest that the study results point to a link with age-related diseases, such as Alzheimer’s, often appearing around 60.

“The [health] decline from age 60 is thought to reflect a change in tissue-specific metabolism, the energy expended on maintenance,” they wrote, according to NBC News. “It cannot be a coincidence that the increase in incidence of noncommunicable diseases and disorders begins in this same time frame.”