Metabolic age, BMR and the InBody Score: what the numbers mean

Many scales show a metabolic or body age. What that number is, what BMR really measures, how muscle changes it, and what the InBody Score sums up.

By Udbhav Kamath9 November 20266 min read

A man holds a plank on a mat in his living room, with a Soft White Dial H30 on the floor in front of him.

Metabolic age is a number some scales show to tell you whether your body is “older” or “younger” than your birthday. It is not a medical measurement, and there is no single agreed formula. Each brand builds its own, and one common approach compares your estimated basal metabolic rate with averages for people of different ages.

It can be motivating. It can also mislead. The more useful numbers sit underneath it: your basal metabolic rate, or BMR; the muscle that drives it; and, on InBody Dial, an InBody Score that sums up muscle against fat. Here is what each one tells you, and which to watch.

The short version

Metabolic age, or body age, is a brand’s summary built on estimates. Treat it as a nudge, not a verdict.
BMR is the energy your body burns at rest. It depends mostly on how much lean tissue you carry, which is why muscle matters.
The InBody Score is one score for muscle against fat. 80 is the starting line; more muscle and less fat push it up.

What “metabolic age” on a scale really is

A body composition scale measures one thing directly: how your body resists a tiny electrical current. Everything after that is calculated. The scale estimates your lean and fat mass, works out a BMR from them, and then, if it shows a metabolic age, compares that BMR with the averages its makers chose.

Each step adds assumptions. By the time a scale prints a metabolic age, it is three calculations away from what it actually measured.

That is why two brands can give the same person quite different ages, and why the number can shift after a salty dinner. It is not that the idea is useless. It is that the label sounds like a fact about your body when it is really a presentation choice.

The InBody app also shows an InBody Age. Treat it the same way: a friendly summary to watch over months, not a measurement to quote.

What BMR actually is

Basal metabolic rate is the energy your body uses at complete rest to stay alive: breathing, pumping blood, running the brain, keeping you warm. For most people it is the largest share of what they burn in a day, larger than exercise.

BMR is usually estimated, not measured. Common equations, such as the Mifflin–St Jeor equation published in 1990, use weight, height, age and sex. That works for the average person but misses differences in what the weight is made of. A Dial works out your BMR from your lean mass and updates it at every test, so when your muscle changes, your BMR changes with it.

The InBody app test summary on a phone, with tiles for weight, skeletal muscle mass, percent body fat, body fat mass, BMI and basal metabolic rate. — BMR sits in the app’s test summary, in kcal, beside weight, muscle and body fat.

How muscle changes BMR, and by how much

Muscle uses more energy at rest than fat does. Researchers estimating the resting energy use of different tissues put skeletal muscle at about 13 kcal per kilo per day, and fat at about 4.5.

Tissue values from Wang et al., 2010. Muscle burns about three times more than fat at rest, but the totals are modest. The bigger payoff of muscle is what it lets you do.

So adding two kilos of muscle raises your resting burn by roughly 26 kcal a day. That is real, but it is a small biscuit, not a meal. The idea that muscle “burns hundreds of calories while you sleep” does not hold up.

The bigger effect runs the other way. When you lose weight, your body gets smaller and uses less energy, and modelling work by Kevin Hall and colleagues shows why weight loss slows over time. If part of that loss is muscle, you lose strength and some resting burn with it. Keeping muscle while you lose fat is the part you control. Our guide to measuring muscle mass at home covers how.

What the InBody Score sums up

The InBody Score is one score for muscle against fat. 80 is the starting line, and it climbs as muscle goes up and fat comes down. Every other number in the app sits against its own standard range; the score rolls the main picture into one figure you can glance at.

The score summarises muscle against fat. It can rise while your weight stays the same, which is exactly the change a weighing machine cannot see.

Because it weighs muscle and fat against each other, the score can climb when the scale does not move at all. That makes it a good companion for anyone doing strength training, or anyone stuck on a weight-loss plateau.

The InBody app showing an InBody Score of 74 points above a skeletal muscle and fat analysis, beside a body type chart of BMI against percent body fat. — The InBody Score sits above your muscle and fat analysis. The body type chart beside it is on Dial H30 and H40.

If you like a little competition, the app has optional rankings. They stay off until you join, and only your InBody Score is ever shown, never your weight or body fat.

The InBody app ranking screen on a phone, showing My InBody Score of 76 points and a weekly score ranking list below. — Rankings compare scores only. Weight and body fat stay private.

Which number should you actually watch?

Treat as a nudge

Metabolic or body age on any scale.
A single day’s BMR.
Any one reading after a festival meal or a late night.

Treat as your scoreboard

Skeletal muscle mass and body fat mass, as monthly trends.
The InBody Score, to see both at once.
BMR across months, to check you are not losing muscle as you lose weight.

Every Dial reports BMR and the InBody Score in the app, along with skeletal muscle mass, body fat and visceral fat level. Dial H20 suits one person. Dial H40 adds leg muscle level and balance ratings for people who train. For why these differ from a normal weighing machine, see BMI machines and body composition scales.

Dial H30 in Soft White from the front, with its dark display window, round dial and four grey foot plates.

Dial H30For the whole house. InBody Score, BMR and 12 readings for up to 20 people, synced over Wi-Fi.See Dial H30 →

Questions people ask

What is a good metabolic age?

Each brand defines it differently, so there is no universal good number. If your scale shows one, compare it only with your own earlier readings and look at the muscle and fat behind it.

Is metabolic age accurate?

It is an estimate built on other estimates, so treat it as a rough summary. The underlying readings, especially skeletal muscle mass and body fat mass, are more useful to track.

Does InBody Dial show metabolic age?

Dial reports basal metabolic rate and the InBody Score, and the InBody app also shows an InBody Age. Treat the age as a summary to watch over time, not a measurement.

What is a normal BMR?

It depends on your size, sex, age and especially your lean mass, so two healthy people can differ a lot. Watch how yours moves as your muscle changes.

Why did my BMR drop when I lost weight?

A smaller body uses less energy, so some drop is expected. If skeletal muscle is falling too, add strength training and check your protein.

What is a good InBody Score?

80 is the starting line. The score climbs as muscle goes up and fat comes down, so a rising score over months is the goal.

Sources

Wang Z et al. Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure. American Journal of Clinical Nutrition 2010;92(6):1369–1377.
Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 1990;51(2):241–247.
Hall KD et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet 2011;378(9793):826–837.
InBody Dial H20, H30 and H40 specifications and InBody app, InBody India.