# Metabolism changes with age aren't what we probably thought they were



## Eddy Edson (Aug 12, 2021)

Big new multi-centre study, looking at infants through 95 year olds. Suprise: Metabolism generally doesn't change between ages of ~20 to ~60. And no general difference between men and women. (When controlled for body size and muscle weight.)










						Metabolism Changes With Age, Just Not When You Might Think
					

DURHAM, N.C. -- Most of us remember a time when we could eat anything we wanted and not gain weight. But a new study suggests your metabolism -- the rate at which you burn calories -- actually peaks much earlier in life, and starts its inevitable decline later than you might guess. The findings...




					today.duke.edu
				




_Energy needs shoot up during the first 12 months of life, such that by their first birthday, a one-year-old burns calories 50% faster for their body size than an adult.

And that’s not just because, in their first year, infants are busy tripling their birth weight. “Of course they're growing, but even once you control for that, their energy expenditures are rocketing up higher than you'd expect for their body size and composition,” said Pontzer, author of the book, “Burn,” on the science of metabolism.

An infant’s gas-guzzling metabolism may partly explain why children who don’t get enough to eat during this developmental window are less likely to survive and grow up to be healthy adults.

“Something is happening inside a baby’s cells to make them more active, and we don't know what those processes are yet,” Pontzer said.

After this initial surge in infancy, the data show that metabolism slows by about 3% each year until we reach our 20s, when it levels off into a new normal.

Despite the teen years being a time of growth spurts, the researchers didn’t see any uptick in daily calorie needs in adolescence after they took body size into account. “We really thought puberty would be different and it’s not,” Pontzer said.

Midlife was another surprise. Perhaps you’ve been told that it’s all downhill after 30 when it comes to your weight. But while several factors could explain the thickening waistlines that often emerge during our prime working years, the findings suggest that a changing metabolism isn’t one of them.

In fact, the researchers discovered that energy expenditures during these middle decades – our 20s, 30s, 40s and 50s -- were the most stable. Even during pregnancy, a woman’s calorie needs were no more or less than expected given her added bulk as the baby grows.

The data suggest that our metabolisms don’t really start to decline again until after age 60. The slowdown is gradual, only 0.7% a year. But a person in their 90s needs 26% fewer calories each day than someone in midlife.

Lost muscle mass as we get older may be partly to blame, the researchers say, since muscle burns more calories than fat. But it’s not the whole picture. “We controlled for muscle mass,” Pontzer said. “It’s because their cells are slowing down.”

The patterns held even when differing activity levels were taken into account.

For a long time, what drives shifts in energy expenditure has been difficult to parse because aging goes hand in hand with so many other changes, Pontzer said. But the research lends support to the idea that it’s more than age-related changes in lifestyle or body composition.

“All of this points to the conclusion that tissue metabolism, the work that the cells are doing, is changing over the course of the lifespan in ways we haven’t fully appreciated before,” Pontzer said. “You really need a big data set like this to get at those questions.”_


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## Eddy Edson (Aug 13, 2021)

Thread from co-lead author John Speakman: 



__ https://twitter.com/i/web/status/1426024218433626119
The really bad thing about this study is the fact that I'm 60 yrs old and the data shows a definite cliff which you fall off at that age, metabolically speaking


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## Northerner (Aug 14, 2021)

Eddy Edson said:


> The really bad thing about this study is the fact that I'm 60 yrs old and the data shows a definite cliff which you fall off at that age, metabolically speaking


And I'm 62, rapidly approaching 63  I have definitely noticed changes since I turned 60. I have always been on the skinny side - I was regarded as 28 lbs underweight aged 25 - but my weight gradually increased as I built up a bit of muscle from running marathons. My ideal weight is around 140 lbs, but I'm currently 170  All the weight goes on my midriff, and I think the weight increases over the past couple of years has been through reduced activity - I find it hard to maintain the levels I had in my 40s and 50s because I either get injured or just too tired!


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## Eddy Edson (Aug 14, 2021)

Northerner said:


> And I'm 62, rapidly approaching 63  I have definitely noticed changes since I turned 60. I have always been on the skinny side - I was regarded as 28 lbs underweight aged 25 - but my weight gradually increased as I built up a bit of muscle from running marathons. My ideal weight is around 140 lbs, but I'm currently 170  All the weight goes on my midriff, and I think the weight increases over the past couple of years has been through reduced activity - I find it hard to maintain the levels I had in my 40s and 50s because I either get injured or just too tired!


You'd hope that having identified the issue these guys would then say how to fix it.  Maybe "Part 2" will include their recipe for curing aging 

I'm pretty sure that it will get cured at some point, but too late for us, no doubt. Which is a pity, because looking at the youngsters around here I reckon immortality would be wasted on them ...


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## Eddy Edson (Aug 19, 2021)

Paper is now open access: https://science.sciencemag.org/cont...df?ijkey=oYUAGierHBtog&keytype=ref&siteid=sci

And a thread from co-lead Herman Pontzer:  



__ https://twitter.com/i/web/status/1428203321215574018


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## Eddy Edson (Dec 3, 2021)

Balancing that, a fascinating hypothesis arising from the same broad research community:









						Evolution Explains Why Exercise is Essential, Especially as We Age.
					

High levels of physical activity may become even more important for health as one gets older, as suggested by a new paper on something biologists call the “active grandparent hypothesis."




					bradyholmer.substack.com
				




_In a new paper, Lieberman and colleagues propose a hypothesis on why physical activity promotes such large increases in healthspan and lifespan. They don’t seek to explain the mechanisms by which PA reduces disease risk factors, but go a layer deeper to posit an evolutionary explanation underlying why physical activity stimulates health-promoting, adaptive processes in the first place. Why did activity evolve to be beneficial?

Central to this discussion is something called the “Active Grandparent Hypothesis.” With the origin of hunting and gathering among our recent ancestors came an increase in physical activity — primarily aerobic physical activity (i.e. walking). This may have introduced a selection for increased physical activity, on the one hand.

At the same time, human lifespans began to increase significantly — well beyond the postreproductive years — the point at which many other animals begin the decline into disability and death. Grandparents thus became an invaluable source of knowledge and wisdom which they could impart to younger generations.

But as this new hypothesis suggests, it was physically active grandparents who may have been the most valuable asset for the community and therefore, a tendency for high levels of PA among middle-aged and older adults was selected for.
_
On this view, we're supposed to be like these hunter gatherers as we age:_

.







... _and not like western oldies lolling around in barcaloungers.  

Also, you can start being more active later in life. There's no cut off date.


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