Metabolic Age: What It Means and How to Improve It

Metabolic age is a number some smart scales and body composition analysers give you, comparing your basal metabolic rate (BMR), the energy your body uses at rest, with the average BMR for people of your actual age. Researchers describe it as an estimation of a person's age based on their basal metabolic rate. If your metabolic age comes out lower than your real age, the scale is suggesting your resting metabolism looks like that of a younger person; if it's higher, the reverse.

It can be a motivating number to watch, but it's an estimate made by a device, not a medical test or diagnosis. Below, we explain how metabolic age is worked out, what it can and can't tell you, what the research says, and the everyday habits linked with a healthier result.

What is metabolic age?

To understand metabolic age, it helps to start with BMR. Your basal metabolic rate is the amount of energy your body needs to keep you alive at rest: breathing, keeping your heart beating, maintaining your body temperature and repairing cells. Our guide on how to calculate your BMR explains this in more detail.

Metabolic age takes your estimated BMR and compares it with typical BMR values for different age groups. In a 2024 study published in the journal Nutrients, researchers defined it as "an estimation of a person's age based on their basal metabolic rate (BMR)".

So, for example, if you're 45 and your scale tells you your metabolic age is 52, it's estimating that your resting energy use is closer to the average for people in their early 50s. A result of 38 would suggest the opposite.

How is metabolic age measured?

Most people come across metabolic age on a body composition scale at home or in a gym. These scales use a technique called bioelectrical impedance analysis (BIA). You stand barefoot on metal pads (and sometimes hold handles), and the scale passes a very small electrical current through your body. Because fat, muscle and water conduct electricity differently, the device uses the resistance it detects, together with details you enter such as your age, sex and height, to estimate your body composition. It then uses formulas to estimate your BMR and, from that, your metabolic age.

Both of the research studies we refer to in this article measured metabolic age this way, using bioimpedance analysers. In the Spanish study, metabolic age was measured using a bioimpedance meter, and in a 2021 study in Medicina Clínica, it was based on fat-free mass measured with a bio-analyser.

That matters for how you read the number. Metabolic age is:

• An estimate built on other estimates. The scale doesn't measure your metabolism directly. It estimates your body composition, then estimates your BMR, then compares that with average values.
• Specific to the device. The formulas behind the result are set by each manufacturer, so it's best not to compare a reading from one brand of scale with a reading from another.
• Best used as a trend. If you track it at all, take readings on the same scale, at a similar time of day and in similar conditions, and look at the direction of travel over months rather than day-to-day changes.

Is metabolic age a medical measurement?

No. Metabolic age is a consumer and research metric, not a clinical diagnosis. When the NHS assesses whether someone's weight may be affecting their health, it uses measures such as body mass index (BMI) and waist size compared with height, not metabolic age.

That doesn't make the number meaningless. It can be a useful prompt to think about your muscle mass, activity levels and diet. But a "good" metabolic age doesn't rule out health problems, and a "poor" one doesn't mean something is wrong. If you have concerns about your weight or health, a GP is the right place to start.

What affects your metabolic age?

Muscle and fat-free mass

Because metabolic age is based on BMR, anything that affects your BMR affects the result. One of the biggest factors is your fat-free mass, which is mostly muscle, along with organs, bone and water.

A large international study published in Science in 2021, which pooled measurements of daily energy expenditure from thousands of people across the lifespan, found that total energy expenditure is strongly related to fat-free mass. In other words, people with more fat-free mass tend to use more energy.

This is why two people of the same weight can get very different metabolic age readings. Someone carrying more muscle will usually be estimated to have a higher BMR, and therefore a lower metabolic age, than someone of the same weight with less muscle. If you've ever wondered why the scale number alone doesn't tell the full story, our article on whether muscle weighs more than fat explains the difference between weight and body composition.

Age

It's often said that metabolism slows steadily from your 20s or 30s, but the evidence is more nuanced. The same Science study found that, once differences in body size were taken into account, daily energy expenditure remains stable in adulthood (20–60 yr) … and declines in older adults (60+ yr).

That suggests changes in body composition and how active we are, rather than age alone, explain much of what people notice in midlife. It also means there's a lot within your control.

Sex

In the Spanish study of 8,590 workers, metabolic age increased with chronological age and was higher in males. Because the result is compared against age-based averages, these differences are partly built into how the number is calculated.

Activity and diet

The same study looked at lifestyle factors and found that the most influential factors on metabolic age are physical activity and adherence to the Mediterranean diet. Physical inactivity was strongly associated with a higher metabolic age.

It's worth being clear about what this kind of study can show. It was cross-sectional, meaning it looked at a large group of people at a single point in time. It shows that these factors are linked with metabolic age, but it can't prove that changing them will change your result by a particular amount.

Does metabolic age matter for your health?

Researchers have looked at whether metabolic age relates to other markers of health. In the 2021 Medicina Clínica study of 284 participants, metabolic age was a good predictor of cardiovascular risk, as measured by waist-to-height ratio, and a better predictor than chronological age.

That's interesting, but it's a single, relatively small study, and it used waist-to-height ratio as its measure of risk. Waist-to-height ratio is something you can check yourself with a tape measure, without needing a special scale.

A simpler check: your waist and your height

The NHS advises trying to keep your waist size to less than half your height, and says that if your BMI is under 35, you can use its waist-to-height ratio calculator.

To measure your waist:

1. Find the bottom of your ribs and the top of your hips.
2. Wrap a tape measure around your middle, roughly halfway between these two points.
3. Breathe out naturally and take the measurement, keeping the tape snug but not tight.

Then divide your waist measurement by your height, using the same units. A result under 0.5 means your waist is less than half your height.

How to improve your metabolic age

There's no shortcut or supplement that reliably changes your metabolic age, and you don't need one. The habits linked with a healthier result are the same ones that support your health more generally.

Build and keep muscle

Since fat-free mass is closely tied to how much energy your body uses, keeping and building muscle is one of the most useful things you can do. The NHS recommends that adults do strengthening activities that work all the major muscle groups on at least 2 days a week. That can include:

• Lifting weights or using resistance bands
• Bodyweight exercises such as squats, lunges and press-ups
• Heavy gardening, such as digging
• Yoga or Pilates

You don't need a gym. The NHS strength exercises page has simple routines you can do at home. If you're new to resistance training, our guide to anaerobic exercise explains how strength and high-intensity work fit into a weekly routine.

Move more through the week

In the Spanish study, physical inactivity was strongly linked with a higher metabolic age. The NHS advises adults to do at least 150 minutes of moderate intensity activity a week, or 75 minutes of vigorous intensity activity. Brisk walking, cycling and swimming are all good options, and it's fine to build up gradually.

Eat a balanced, Mediterranean-style diet

The Spanish researchers found that following a Mediterranean diet was linked with a lower metabolic age. A Mediterranean-style way of eating is built around vegetables, fruit, wholegrains, beans and pulses, fish, nuts and olive oil, with less red and processed meat. This is very similar to the NHS's own advice on eating a balanced diet, which recommends:

• Eating at least 5 portions of a variety of fruit and vegetables every day
• Basing meals on higher-fibre starchy foods like potatoes, bread, rice or pasta
• Eating some beans, pulses, fish, eggs, meat and other protein
• Aiming for at least 2 portions of fish a week, including 1 portion of oily fish

Getting enough protein is especially helpful when you're trying to protect your muscle while managing your weight. Our list of high-protein, low-calorie foods has plenty of everyday ideas.

Avoid extreme approaches

Steady, sustainable changes to how you eat and move, which you can keep up for the long term, are a better bet for your health than quick fixes or very restrictive diets.

Look after the basics, including sleep

Good habits are easier to keep up when you're well rested. If you're not sure whether you're getting enough rest, our guide asking is 7 hours of sleep enough? looks at what the evidence says about sleep and weight.

How to read your result without getting hung up on it

A few practical tips if your scale shows metabolic age:

• Don't panic about a single reading. Body composition estimates can shift from day to day. Look at trends over weeks or months.
• Keep conditions consistent. Use the same scale, at a similar time of day, ideally before eating and after going to the toilet.
• Look at the bigger picture. Your waist measurement, how your clothes fit, your energy levels, your strength and your fitness are all meaningful markers of progress.
• Don't compare across devices. A reading from a gym analyser and one from your bathroom scale may not line up.
• Check the safety guidance. Read your scale manufacturer's instructions before using a body composition feature, particularly if you have an implanted electronic medical device.

If you find that tracking numbers makes you anxious, or starts to feel all-consuming, it's fine to switch off the extra metrics and focus on how you feel and what you're doing day to day.

This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before starting any treatment.