They say age is just a number. But what if your body is actually older or younger than the number of candles on your birthday cake? That's the idea behind metabolic age, which compares your body's metabolism to that of other people who have made the same number of trips around the sun.
Or at least that's the promise. At this time, there's not much research around the concept of metabolic age. So while a younger metabolic age seems to indicate a lower risk of health problems, it's best to take all of this with a grain of salt.
Here's what we do know: The things that appear to lower your metabolic age are healthy for you in general, so there's no reason not to do them.
What Is Metabolic Age?
Although metabolic age can be measured in a few ways, most commonly it refers to how your basal metabolic rate (BMR) compares to the average BMR for people of your chronological age (how long you've been living), explains Catherine J. Andersen, PhD, RDN, associate professor of biology at Fairfield University.
So what's basal metabolic rate? That's how many calories you need to sustain your basic vital functions while at rest. It doesn't take into account any extra energy you need to move or do physical activity, Andersen says.
Why Is Metabolic Age Important?
Your metabolic age reflects your physical health. According to a May 2017 study in Transplantation, having a metabolic age lower than your chronological age indicates good health, while a higher metabolic age suggests you may have some health problems.
"A lower metabolic age is typically found in those with more lean muscle tissue, better diet choices and a more active lifestyle, all of which typically indicate a healthier lifestyle," adds dietitian Lauren Minchen, MPH, RDN, CDN.
While much more research is needed, one small study of 19 people in Current Developments in Nutrition in June 2019 found a possible health perk: having a metabolic age lower than your actual age was associated with lower blood pressure.
And in Andersen's lab, "we see an increased metabolic age associated with a higher BMI, waist circumference, body fat mass and blood pressure," she says. "All of these are risk factors for cardiovascular disease, metabolic disease and diabetes."
Why Your Metabolic Age May Be Higher Than Your Actual Age
First of all, BMR is based on your sex, weight, height and age. So carrying some extra pounds for your height may lead to a higher metabolic age.
More advanced and accurate ways of measuring BMR also take into account your body composition. "The biggest thing that results in a higher metabolic age would most likely be lower lean body mass relative to overall body weight," Andersen says.
And of course your diet and exercise habits influence your weight and body composition. So, "your metabolic age may be higher than your actual age if you don't participate in regular exercise, make poor diet choices habitually and don't manage stress well," Minchen says. "These can lead to a loss of lean body tissue, fat gain and a general decline in overall health."
How to Improve Your Metabolic Age
Healthy lifestyle factors can help lower your metabolic age.
1. Be Active
Lean mass is a big factor in metabolic age. To build muscle, hit the weights. Strength training is essential to gain lean body mass.
Plus, being active in general can help keep your weight in check, and a healthy body weight can bring down your metabolic age.
Not sure where to start? Here's everything beginners need to know about building muscle.
2. Eat Enough Protein
Protein supports muscle growth. Especially if you're also trying to lose weight, eating a high-protein diet helps you maintain and build muscle, according to a December 2019 review and meta-analysis in Advances in Nutrition, which suggests aiming for about 1.3 g per kg of your body weight daily.
Keep in mind that 1 pound equals about 0.45 kg. So if you weigh 200 pounds, that's about 90.7 kg. Multiply that by 1.3, and voila: You should aim for about 118 g of protein each day.
Foods high in protein include:
- Fish and seafood
- Beans and lentils
- Yogurt and cottage cheese
3. Prioritize Sleep
"Sleeping at least seven hours per night is essential for supporting a healthy BMR, recovering from exercise, digesting food well and becoming stronger," Minchen says.
"We see the greatest amount of muscle building during sleep," Andersen adds. "So if your goal is to increase lean body mass, adequate sleep will better support that."
Struggle with zzzs? Learn how to fix the 10 most common sleeping mistakes.
4. Manage Stress
"If we don't find ways to properly manage stress, we sleep poorly, skip workouts, make quick and convenient food choices that often make us feel worse later and run our bodies into the ground," Minchen says.
All of that can increase your metabolic age. Plus, increased stress puts our bodies into more of a catabolic state, where it's breaking down nutrient stores, and that could affect our skeletal muscle, Andersen adds.
5. Consider a Plant-Based Diet
In the Current Developments in Nutrition study, eating a diet heavy in plants was associated with a lower metabolic age compared to chronological age.
Ready to change your eating habits? Get started with a seven-day plant-based meal plan.
How to Calculate Metabolic Age
There's currently no standardized way to determine metabolic age, Andersen says. Instead, various calculations and types of proprietary software are used. "I haven't found any that have been truly validated by research," Andersen says.
That said, if you want to calculate your metabolic age, you need access to data of the metabolic age of other people who have the same chronological age as you, because you want to know how you stack up compared to them.
Only some personal trainers, registered dietitians and other experts at medical or fitness centers have the technology to determine your metabolic age. If you're curious to know yours, search online for providers in your area or call around.
The more accepted methods to calculate metabolic age use bioelectrical impedance scales, Andersen says. As you stand on these (or hold onto sensors), they send a low-level electrical current throughout your body. This measures how much lean body mass and how much body fat you have. You can also find bioelectrical impedance scales online to buy for your home, but these vary in accuracy, Andersen says.
You can, however, calculate your BMR using the appropriate formula below:
For people assigned female at birth: (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161
For people assigned male at birth: (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5
Let's say you're someone assigned female at birth who's 30 years old, 150 pounds (68 kg) and 5 feet tall (152.4 cm). Your BMR would be 1,321.50. As a reminder, that's an estimate of the calories your body burns just carrying out its basic functions (breathing, circulating blood), not including moving or any physical activity.
Your metabolic age tells you how your BMR compares to others of your same age. Having a younger metabolic rate seems to indicate a healthier lifestyle and may mean you're at lower risk for certain health conditions. However, we need more research to determine the best way to calculate metabolic age and what exactly it means.
- Transplantation: "High Metabolic Age and Excessive Adipose Tissue as a Storage Location for Toxins, and their Influence on the Excretory Function of a Liver and Bile Ducts in Patients with a Transplanted Allogenic Kidney"
- Current Developments in Nutrition: Younger Relative Metabolic Age Is Associated with a More Favorable Body Composition and Plant-based Dietary Pattern (P21-038-19)
- Advances in Nutrition: "Protein Intake Greater than the RDA Differentially Influences Whole-Body Lean Mass Responses to Purposeful Catabolic and Anabolic Stressors: A Systematic Review and Meta-analysis"