They say that age is less about the number and more about how you feel. Some things will inevitably change as we age, but that doesn't mean we can't age gracefully and healthily. Aging well means you can continue doing the things you love without letting your age get in the way.
Theories of aging and disease are complex, but one emerging principle is the role of metabolism in health and longevity. Metabolism is the set of chemical reactions that occur in living cells to maintain life and slows down as we age. Cellular aging is linked to changes in metabolic health, which is why scientists are interested in studying metabolic rate as a marker of health.
So, where does metabolic age come in? Metabolic age is a measure of how fast or slow your metabolism is relative to other people of the same chronological age.
But is metabolic age something we can measure and track? And if so, what does it reveal about our health? Let's take a closer look.
What Is Metabolic Age?
Chronological age is the number of years you've been alive, while metabolic age measures how well your metabolism functions compared to other people at the same age.¹
A higher metabolic age means someone's metabolic rate is lower than expected for their age. Metabolic age isn't necessarily something your doctor will check, and it's not used for diagnosis. It's more often used by the fitness community to assess overall health and fitness.
In some cases, metabolic age could be a helpful tool to track metabolic health and make lifestyle changes accordingly. Still, getting the number is not always easy (stay tuned for more on calculating metabolic age).
Basal Metabolic Rate and Health
To better understand metabolic age, it's helpful to think about it as another way of examining your metabolic rate.
The number of calories you burn at rest (outside of physical activity) is known as your basal metabolic rate (BMR). BMR is the number of calories your body needs to maintain vital functions such as breathing, heartbeat, and cell growth. It can vary depending on age, gender, muscle mass, genetics, and more.
Some research suggests a person's BMR is an important marker for metabolic health. A lower BMR is associated with an increased risk for metabolic health conditions like diabetes and insulin resistance.²
On the other hand, a higher BMR may also be inversely associated with all-cause mortality, based on the results of another study.³ In other words, a higher metabolic rate is linked to living longer.
Your Basal Metabolic Rate Changes with Age
Recent research suggests that metabolism drops regardless of body size as we age. Scientists discovered four significant phases of metabolic rate change in life. Up to age one, metabolic rate is high, but once a child hits their first birthday, metabolic rate drops by nearly 3 percent a year until age 20.⁴
No major changes occur from your 20s through your 50s, but once you hit 60, your metabolic rate drops by just under one percent a year. In this study, metabolic rate varied within each age group—meaning two people at a certain age could have very different rates. But the overall declining pattern remained the same for everyone even after controlling for things like body weight.
What does this mean? It means that some change to metabolic rate is inevitable with age, so working on keeping your metabolism as healthy as possible to offset these changes is essential.
How to Calculate Your Metabolic Age
The truth is that it's challenging to calculate metabolic age on your own because the most accurate measures of BMR require special equipment that's not readily available.
You can estimate your BMR using calculations like the Harris-Benedict equation that considers age, gender, height, and weight (there are many online calculators, so you don't have to do it by hand). But unfortunately, even experts admit that these predictive equations are moderately accurate at best and lead to many errors in estimating someone's actual metabolic rate.⁵
An accurate method for measuring BMR is indirect calorimetry, which involves wearing a mask connected to a machine. The machine measures the amount of oxygen you inhale and the carbon dioxide you exhale to estimate your BMR. But many people don’t have access to this machine.
In reality, metabolic age isn't quite ready for primetime as a major marker of health. That said, if you do have access to metabolic testing, it could be an interesting piece of information to track.
What Your Metabolic Age Tells You About Your Health
Let's say you can measure your metabolic age. What can it tell you? A lower metabolic age means your metabolism is functioning at a level comparable to people younger than you chronologically.⁶
Of course, many factors affect metabolism besides age, including muscle mass, weight, hormones, and genetics. So, your metabolic age isn't necessarily a perfect reflection of your health.
But what does science say? There isn't much research on metabolic age, but a few interesting studies exist. One study that assessed metabolic age as a predictor of heart disease found that people with higher metabolic age have a higher risk of developing heart disease.⁶
Some research has also found an interesting correlation between high metabolic age and a higher risk of developing metabolic syndrome.¹
Metabolic syndrome refers to a group of conditions like insulin resistance, high waist circumference, high blood pressure, and high cholesterol that increase the risk for chronic disease.
Scientists also found that younger metabolic age is associated with lower body weight, BMI, systolic blood pressure, and waist circumference.⁷
With this in consideration, metabolic age could be a marker for metabolic health—but it's not the only way to measure it.
Factors That Increase Metabolic Age
We've established that metabolic age isn't an easy number to track. But let's consider that metabolic age is a reflection of metabolic health. It makes sense that certain lifestyle factors would increase or decrease metabolism (and therefore metabolic age), such as:
- Nutritionally poor diet. Certain diet patterns (think highly processed foods without fruits, veggies, whole grains, healthy fat, and protein) can adversely affect metabolic health.
- Lack of exercise. Exercise helps to increase muscle mass, which can boost metabolism. It also helps to improve insulin sensitivity and reduce inflammation.⁸
- Stress. Chronic stress can lead to weight gain, insulin resistance, and inflammation.⁹
- Crash diets. Surprised to see this here? Drastically cutting calories or jumping on and off the latest restrictive diet can backfire by slowing your metabolism. These diets don't work, aren't personalized to you, and aren't sustainable long-term.
Can You Decrease Metabolic Age?
On the other hand, some lifestyle factors can improve metabolism—translating to lower metabolic age— and better metabolic health:
- Move your body every day. Combining aerobic exercise and strength training has been shown to increase BMR. Why? Physical activity helps increase muscle mass which can improve metabolic rate.
As we age, muscle mass begins to decline, accelerating the drop in metabolic rate. This is why it's important to strength train as we age to help preserve muscle mass (and metabolic rate).¹⁰
- Get enough shut-eye. Sleep is crucial for overall health, including metabolism. Sleep deprivation can alter metabolic rate, increase the risk of type 2 diabetes, and adversely impact hormones.¹¹
- Manage stress levels. There's so much talk about self-care and stress management. But what does that really mean? It doesn't have to be meditation or journalling, it just needs to be something that brings calm and even joy to your life.
If the idea of stress management stresses you out, keep it simple. Call a best friend, laugh with your kids, or have a dance party in the living room. Find what works for you.
- Eat enough protein. Protein is essential for maintaining muscle mass, especially as we age. Try to include protein at every meal—chicken, fish, lentils, eggs, yogurt, cottage cheese, and beans are all good options.
Will Losing Weight Improve Metabolic Age?
Losing weight doesn't automatically improve metabolic age. But it could.
If you lose weight in a healthy way—eating nutritious foods, exercising regularly, and managing stress—metabolic age could improve by increasing lean body mass and improving insulin sensitivity.
But more important, healthy lifestyle changes that naturally support weight loss can improve overall metabolic health, which is likely a better marker of health.
On the flip side, if you lose weight in an unhealthy way—crash dieting or yo-yo diets—metabolic age could increase as your metabolism slows down.
Metabolic Age: Is It Important?
After reading all of the above, you may wonder if metabolic age is actually an important number you need to know?
Not necessarily. It could be a way to assess your health if you have access to tools to accurately evaluate your BMR. But markers of metabolic health like insulin resistance, inflammation, and body composition are likely more important.
That said, if you want to track metabolic age to motivate yourself to live a healthier lifestyle, there's no harm in that. Lifestyle choices that improve metabolic health—eating nutritious foods, exercising regularly, getting enough sleep, managing stress—will also help to improve metabolic age.
Keep the focus on making healthy lifestyle choices, and you'll set yourself up for better metabolic health at any age.
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