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Many of us now carry a little more weight than we did in our 20s. As tempting as it is to attribute this weight gain to a slowed metabolism, according to a. may not be the case Study published last week in the journal Science.

In this study, scientists found that once you adjusted your weight and body fat percentage, metabolic rates remained stable between the ages of 20 and 60. That means your body doesn’t change how many calories it burns during this time just because your age – your metabolism instead depends on your height and the amount of body fat versus lean mass you are carrying.

Why we still learn how our metabolism works

If you’re wondering how a single study can turn everything we believed we knew about our metabolism on its head, it’s because most of our conventional wisdom is not based on solid, verified evidence. The reason is that the studies that can answer these questions are expensive, making it impossible to get a sample size large enough to provide a rigorous, evidence-based answer to how our metabolism changes with age.

“It is hard to believe that in 2021 a paper that reads ‘This is how metabolism changes with body size and over the course of life’ is new,” said Hermann Pontzer, an associate professor of evolutionary biology at Duke University who was a lead author on the study. “We weren’t able to determine the sample sizes. Getting even 100 people into a metabolism study is usually considered a pretty large number. “

To obtain these figures, Pontzer, together with around 80 employees, combined data from several laboratories with the “double-labeled water” method, which is considered the gold standard in the field of metabolic studies. They created a database with the metabolic data of more than 6,400 study participants aged between 8 days and 95 years.

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“We never had these numbers to play with,” said Pontzer.

This gave them a sample size large enough to finally answer the question of how our metabolism changes in the course of our lives.

How your metabolism changes over the course of your life

They found that after adjusting for weight and body fat percentage, our metabolism peaks at the age of 1 year, decreases by about 3% per year until you are 20 years old, then remains stable for the next 40 years and then decreases by about 1% per year.

In terms of our own metabolism, your daily energy needs will not change if your weight and body fat percentage remain the same during this time. However, if you maintain the same weight but replace some of your muscle mass with fat, your body will need more energy every day. However, this change would be a factor of weight and body fat percentage rather than a fundamental change in your metabolism.

At the cellular level, “your cells are just as busy at 50 as they are at 20,” said Pontzer. However, once you hit 60, your metabolism changes fundamentally, with your cells using a little less energy over time.

The good news is that weight and body fat percentage are factors that you can change. For example, if you have more muscle mass now than you were in your 20s, it would mean that your body needs more daily energy today than it did back then.

They also found that once men and women adjust to their weight and body fat percentage, they burn calories equally. Granted, women tend to have higher body fat percentages than men, but if you compare men and women who have the same weight and body fat percentage, “they’d have the same amount of energy on average,” said Pontzer.

What to Focus On When Gaining Weight

In practice, this means that weight gain is not because your metabolism is slowing down. Instead, other factors are likely to play a role, such as diet and exercise, which, given all the adult pressures that began to emerge in the 30s and 40s, are all too easy to let go of.

This study doesn’t go into why we often gain weight as we age, but it reassures us that a slowed metabolism isn’t the reason. It also gives us a simple (if not easy) roadmap for adjusting our weight: Losing fat and / or increasing muscle mass will keep our calorie consumption high. That means healthy eating and Strength training are especially important as we get older.

When faced with a pantry full of highly processed foods after a long, busy day juggling work, family, and other commitments, it’s easy to eat a little extra while struggling to find the time to do the activity Your body needs to maintain your muscle mass. That adds up over time.

The good news is that the database that enabled Pontzer and his coworkers to finally answer those questions about our metabolism is now publicly available, which means that any scientist who wants to use the data can do so for as long as theirs Adhere to all ethical guidelines for use of patient data based on proposed research. That means we can learn even more about how our metabolism actually works in the years to come.

“The surprise of this work is not that it contradicts previous data because there was simply no data,” said Pontzer. “The surprise is that biology surprises in ways that you don’t expect when you measure this. I think there will be a lot to learn here. ”