"Green tea boosts your metabolism." "Don’t eat after 7 pm." "Work out
on an empty stomach." We are surrounded by myths when it comes to talking about the
way our bodies burn energy. Another common one is that your metabolism is doomed to go
downhill after you become an adult. But the good news is that might not actually true.
Every minute of every day, your body is converting food or stored fat into energy to keep itself
going— doing things like pumping blood, expanding and contracting
your lungs, plus all kinds of stuff on a cellular
level, like making new cells and getting rid of old ones. This is your basal metabolic
rate. On top of that, there’s the energy you expend
to move around and do the physical activity of your day…plus the energy it takes to
process your food into energy in the first place.
The exact amount of energy it takes to do all this varies from person to person. If
someone burns through a lot of energy in a given amount of time, we say they have a fast
metabolism. Those who burn less energy in the same amount of time have a slow
metabolism. There are so many crash diets and ‘quick
fixes’ that promise to speed up your metabolism to help you achieve weight loss, but the truth
is that the speed of your metabolism is determined almost entirely by your genes.
And research is also telling us that metabolism actually plays a relatively small role in
weight management anyway—the biggest factors for this are good ol’ diet and exercise.
So how about that “our metabolism gets slower
as we age” factoid? Well, for years it was widely accepted by the scientific community,
but a 2021 study has given us a much-needed update. A team of 80 co-authors analyzed metabolic
rate data collected by different labs over the course of 40 years. This data comes from
more than 6,400 people ranging from 8 days old to 95 years old.
Turns out, there are metabolic shifts in our lives, just probably not when you think. Our
calorie-burning peak is actually when we’re infants, when from birth to 15 months we’re
using crazy amounts of energy to grow our brains and our bodies. Infants actually burn
calories 50% faster than adults! After these early days, our metabolism slows down throughout
childhood and adolescence before it settles around age 20 into our adult rate. Then at
60 years old, our metabolic rate drops again, and keeps declining until the end of our lives.
But between 20 and 60, that big span of time in the middle...our metabolism stays pretty
much the same, even through big changes like pregnancy or menopause. Your metabolism may
be different from someone else’s, but it’ll be pretty much the same throughout your adulthood.
That means that when we do see weight changes as we age, it’s likely not due to metabolic
shifts directly, but the countless other things that can affect the way our body stores energy—
stuff like stress, sleep quality, genes, medications, diet and so much more.
While this new data can help us cut through the crap of ‘magic metabolism boosting pills’
or blaming weight gain on middle age, it also lays the groundwork for some really cool medicine.
Now that we know about the metabolic decline after 60, we can look into specialized ways
of prescribing medication that takes metabolic decline into account. The other end of the
age spectrum may hold some answers too—early life metabolic rates could tell us what an
infant’s weight gain might mean for their health as an adult.
Research like this could hold the keys to tackling health issues like obesity
and malnutrition too. And because metabolism is really a process at the cellular level, if
stuff goes wrong here it can result in issues like cancer. So knowing more about
how this all works throughout someone’s life is about so much more than just weight.
This study offered us many data points, but each from a different person at a different point
in their own life. The next steps could be to follow the same person over time. Doing this
with multiple people, over long periods of time, is a really difficult research
endeavor, so you can see why we don’t have a lot of clear data in this area yet.
It gets more complex when researchers want to take an even closer look too, like the activity
of specific genes, the immune system, even gut microbiome composition
and brining all these variables together.
Why it stays steady, what’s happening in those periods of growth spurt and decline
at the bookends of our lives, how and why metabolism differs so much from individual
to individual—these are the questions that we'll hopefully get some answers soon
and get us closer to our healthiest selves.
So… how do our bodies actually transform
food into energy? Check out our Human episode about that here. And if there's another health science
topic you want us to cover, let us know in the comments.
Don’t forget to subscribe, thanks so much for watching
and I’ll see you next time on Seeker.