Why Slowing Metabolism Probably Doesn’t Lead to Weight Gain
Many of us carry a little more weight now than we did when we were 20. However, as tempting as it is to blame slow metabolism for weight gain, this may actually not be the case, according to a study published last week in Science .
In this study, scientists found that after adjusting for weight and body fat percentage, the metabolic rate remained stable between the ages of 20 and 60. This means that during this time your body does not change the amount of calories it burns just because of your age – on the contrary, your metabolism depends on your body size and the amount of body fat compared to the muscle mass that you carry.
Why We Are Still Studying How Our Metabolism Works
If you’re wondering how one study could turn around everything we thought we knew about our metabolism, that’s because much of our conventional wisdom isn’t based on solid, substantial evidence. The reason for this is that the research that can answer these questions is expensive, making it impossible to get a large enough sample to offer a rigorous, fact-based answer about how our metabolism changes with age.
“It’s hard to believe that in 2021 an article that says, ‘This is how metabolism changes with body size and lifespan,’” said Herman Pontzer , assistant professor of evolutionary biology at Duke University, who was one of them. … leading authors of the study. “We were unable to obtain sample sizes. Involving even 100 people to study metabolism is usually considered a fairly large number. “
To obtain these numbers, Pontzer, along with about 80 collaborators, combined data from several laboratories using the double-labeled water method, considered the gold standard in metabolic research. They compiled a database containing metabolic data for more than 6400 study participants, ranging in age from 8 days to 95 years.
“We didn’t have numbers like that before,” Ponzer said.
This gave them a large enough sample size to finally answer the question of how our metabolism changes over the course of our lives.
How your metabolism changes over time
They found that after adjusting for weight and body fat, our metabolism peaks at 1 year old, declines by about 3% per year until you turn 20, then remains stable for the next 40 years, after which it will decline. … by about 1% per year.
As for our own metabolism, if your weight and body fat percentage remain the same during this time, your daily energy requirements will not change. However, if your weight stays the same, but some of your muscle mass is replaced by fat, your body will need more energy every day. However, this change will be more of a factor in weight and body fat percentage than a fundamental change in your metabolism.
At the cellular level, “your cells are as busy when you are in your 50s as when you were in your 20s,” Ponzer said. However, once you turn 60, your metabolism does change at a fundamental level, and your cells use slightly less energy over time.
The good news is that weight and body fat percentage are factors that you can change. For example, if you now have more muscle mass than 20, it means your body will have a higher daily energy requirement now than it did then.
They also found that after adjusting for weight and body fat percentage, men and women burned calories at the same rate. Of course, women tend to have a higher percentage of body fat than men, but if you compare men and women with the same weight and the same percentage of body fat, on average, “they will have the same energy expenditure,” said Ponzer.
What to focus on if you gain weight
In practice, this means that if you gain weight, it is not because your metabolism is slowing down. Instead, other factors are likely to come into play, such as diet and exercise, which are all too easy to miss due to the adult pressure that tends to occur in your 30s and 40s.
This study does not explain why we often gain weight as we age, but it does provide confidence that metabolic slowdown is not the cause. It also gives us a weight management plan that is simple (if not easy): losing fat and / or increasing muscle mass will keep your calorie burning rates high. This means that healthy eating and strength training are especially important as you age.
When, after a long, exhausting day of work, family, and other responsibilities, you come across a pantry filled with high-tech food, it’s easy to eat a little more while struggling to find time to do something. your body needs to support your muscle mass. It adds up over time.
The good news is that the database that allowed Ponzer and his collaborators to finally answer these questions about our metabolism is now publicly available, which means that any scientist who would like to use the data can, if their proposed research adheres to all ethical principles for the use of patient data. This means that we will be able to learn even more about how our metabolism actually works in the coming years.
“The surprise about this work is not that it contradicts previous data, because the data just wasn’t there,” Ponzer said. “The surprise is that when you go and measure it, biology is unexpected. I think there is a lot to learn here. “