An RMR test measures one number: how many calories your body burns at complete rest. It takes about ten minutes of lying still and breathing normally, and it replaces a formula’s estimate of that number with a measurement.

Two things up front, before you read any further. We do not measure resting metabolic rate at BTX. We refer clients to a provider who does, because indirect calorimetry done casually is worse than no test at all. And no trial has shown that measuring your resting metabolic rate improves your results. It is a useful input, not an intervention.

This page covers what the test actually measures, why the BMR figure already printed on your body composition sheet is not the same thing, and when the upgrade from an estimate to a measurement is worth making.

Expertise reviewed by James Cooper, Founder and CEO at Body Transformation London. BSc Nutrition, King’s College London.

What is resting metabolic rate?

It is the energy your body uses keeping you alive while you do nothing: heart, brain, kidneys, liver, breathing, holding temperature. It is what your body burns before any movement, training or digestion is added on top, and it is not your total daily expenditure, which includes all three.

That distinction matters, because most calculators start from a resting figure and multiply it, so an error at the start travels through everything built on top of it. Our guide to losing fat without losing muscle covers what you actually keep and lose on the way down.

Your scan sheet already prints a BMR figure. Is that a measurement?

No. It is an equation, and this is the single most common misreading of a body composition printout.

Every InBody 270 result sheet carries a basal metabolic rate box, and clients routinely treat it as a measured calorie target. The official InBody 270 training manual is explicit that the device “uses the Cunningham equation to determine the BMR using a known regression equation based on the amount of LBM an individual has”. So the machine estimates your lean body mass from impedance, then runs that estimate through a population regression. Nothing about your breathing, your gas exchange or your actual energy production was measured at any point.

That is not a scandal and it is not a reason to distrust the rest of the sheet. A regression from lean body mass is a sensible way to estimate a resting figure. It is simply an estimate built on another estimate, and it deserves the same caution as any other estimate. We take the same line with every other box on that printout in our guide to how to read your InBody results.

The upgrade path is the useful part. A body composition scan gives you an estimated resting figure in half an hour. Indirect calorimetry gives you a measured one. The rest of this page is about when that upgrade earns its place, and for a lot of people the honest answer is that it does not.

How is metabolic testing done?

Indirect calorimetry measures what you breathe. Energy production consumes oxygen and produces carbon dioxide in a fixed relationship, so gas exchange at your mouth reveals how much energy you are producing.

The protocol is where cheap testing falls down. Food, alcohol, caffeine and nicotine all shift resting metabolic rate for a variable number of hours and must be controlled beforehand. You then rest quietly for 10 to 20 minutes before recording starts. The measurement itself runs about 10 minutes, with the first 5 discarded, because that is when breathing is still settling (Compher et al., 2006).

Preparation is most of the accuracy. Walk in with a flat white in hand and straight onto the machine and you have bought a number, not a measurement. This is also why we refer rather than improvise: a protocol like that has to be run the same way every time by someone who does it all day.

Why measure when the formula is free?

Because formulas describe groups well and individuals poorly.

Mifflin-St Jeor is the standard equation. In 337 adults it was unbiased at group level, with a 95% confidence interval of minus 26 to plus 8 calories a day. But accuracy was lower in participants with obesity, whichever equation was used (Frankenfield, 2013). In 125 women it showed zero bias with a standard deviation of 153 calories a day, and predicted 71% of individuals within 10% of their measured value (Thom et al., 2020).

Read that 71% the other way round. Roughly three people in ten are estimated wrong by more than 10%, and the equation gets less accurate in exactly the group most likely to be dieting.

The same logic applies to the Cunningham figure on a scan sheet. It is a population regression, so it is a good description of people like you and a rougher description of you.

What a measured RMR honestly cannot do

It cannot tell you your metabolism is broken, and it cannot promise faster fat loss. No trial has shown that measuring beats estimating for outcomes, and anyone saying otherwise is selling. What it does is remove one source of error.

Has your metabolism adapted to dieting?

Adaptation is real, but a systematic review of 33 studies and 2,528 participants put it at roughly 30 to 100 calories a day in resting energy expenditure, with the televised weight-loss studies the stated exception at 200 to 300, and found it attenuated or non-existent after a period of weight stabilisation (Nunes et al., 2022). The widely quoted 499 calories a day comes from 14 people, “your metabolism is permanently broken” is not supportable, and our guide to keeping weight off after rapid weight loss takes the argument apart properly.

RMR test London: what a measured figure changes

A resting figure is only worth having if it changes something. Here is what it changes.

It replaces an estimated figure with a measured one as a reference point, and gives you something objective to re-measure against. Setting an individual calorie prescription is dietetic work, and we refer for it.

Around that:

• Your expectations. A lower-than-expected value is an argument for patience and a gentler approach, not for cutting harder.
• What sits next to it. A resting figure alone is thin, and reads far better beside an InBody body composition scan and tape measurements, because no instrument is good enough alone.
• What you compare against. Measured once on a controlled protocol, it can be measured the same way again months later, which is the only version of this test that says anything about change.

Who is an RMR test worth doing for?

Worth considering if you have dieted repeatedly and stalled at an implausibly low intake, if you are training hard and the measurements are not moving, or if you prefer decisions built on a measurement rather than an estimate.

Probably not worth it yet if you have never tracked your intake consistently. A test cannot fix an unrecorded diet.

And to be blunt about it: for most people, most of the time, the estimated figure is fine. Mifflin-St Jeor is unbiased at group level and the Cunningham figure on your scan sheet is a reasonable starting point. If your intake is not tracked, your training is inconsistent and your protein is low, a measured resting metabolic rate will not be the thing that changes your year.

Can you get an RMR test at BTX?

Not on site, and we would rather say so than blur it. BTX does not measure resting metabolic rate in house. We have a referral arrangement with a provider who does, and if a measured figure is your right next step, that is where we will send you.

Indirect calorimetry needs the right equipment, a controlled environment and someone who runs the preparation protocol identically every time. That is not something you do adequately as a sideline between coaching sessions, and a badly run test produces a confident-looking number that is simply wrong. We would rather refer you to somebody who does it properly than sell you a figure we estimated badly ourselves.

What we do after the referral is the part that is genuinely ours: reading that number next to your scans, your tape measurements, your strength log and what you are actually eating, and building a programme around the whole picture rather than one line of it.

We coach at 529a Finchley Road, in easy reach of Hampstead, West Hampstead, South Hampstead, Belsize Park, Primrose Hill, Swiss Cottage, St John’s Wood and Golders Green. Ask us on a call whether a referral makes sense for you, and we will tell you honestly if it does not.

A note on scope

Our coaches are coaches. In the UK, “dietitian” is the only legally protected nutrition title. Individual calorie prescriptions, clinical interpretation of results and anything for a medical condition sit outside coaching scope, and we refer for those rather than improvise. We do not diagnose or prescribe. If you are between 40 and 74, the free NHS Health Check covers height, weight, waist measurement, blood pressure and cholesterol every five years, and is the sensible starting point for the medical side.

Book a call

If you want your training and nutrition measured properly and programmed around by someone still there in twelve weeks, book a call about body recomposition coaching. We will tell you honestly what is worth measuring in your case, what we measure ourselves, and what we send you elsewhere for.

Free InBody scan until 30 September

We are running complimentary body composition scans at our Finchley Road studio, Monday to Friday between 10am and 2pm. Thirty minutes: the scan itself, plus a coach taking you through what your numbers mean and which ones to ignore. No charge, no obligation, one per person.

Book your free scan or see what’s included.

This article is general information, not medical advice. If you have a medical condition, are pregnant, are taking any prescribed medication, or have a history of disordered eating, speak to your GP or a registered dietitian before changing how you train or eat.

Frequently asked questions

Does BTX do RMR testing?
Not in house. We do not measure resting metabolic rate at the studio. We have a referral arrangement with a provider who does measure it, and we will point you there if a measured figure is worth having in your case. Everything after the test, reading it alongside your scans, training and food, is ours.

Is the BMR number on my InBody sheet my resting metabolic rate?
It is an estimate of it, not a measurement. The InBody 270 training manual states the device uses the Cunningham equation, a regression based on how much lean body mass you have. Your lean body mass was itself estimated from impedance, so it is an estimate built on an estimate. Useful as a starting point, not a measured calorie target.

How much does an RMR test cost?
We do not publish a figure. Since we refer rather than test, the fee is the testing provider’s rather than ours, and it varies with whether a test is sold on its own or inside a wider assessment. Ask on a call and we will tell you what we know.

How is metabolic testing done?
By indirect calorimetry. You rest quietly for 10 to 20 minutes, then breathe normally for about 10 while oxygen and carbon dioxide are measured, the first 5 minutes discarded. Food, alcohol, caffeine and nicotine must be controlled beforehand (Compher et al., 2006).

What should I ask a provider before booking an RMR test?
How long you rest before recording begins, whether the opening minutes are discarded, and what you are told to avoid beforehand. Those answers tell you whether you are buying a measurement or a printout.

Will an RMR test show that my metabolism is damaged?
No. Adaptation is real but typically 30 to 100 calories a day, and appears attenuated or absent after weight stabilisation (Nunes et al., 2022). The 499 calories figure comes from 14 people and is an outlier.

Sources

• Compher C et al. Journal of the American Dietetic Association, 2006. https://doi.org/10.1016/j.jada.2006.02.009
• Thom G et al. Journal of Nutritional Science, 2020;9:e17. https://doi.org/10.1017/jns.2020.11
• Frankenfield DC. Clinical Nutrition, 2013. https://doi.org/10.1016/j.clnu.2013.03.022
• Fothergill E et al. Obesity, 2016;24(8):1612-1619.
• Nunes CL et al. British Journal of Nutrition, 2022;127(3):451-469. https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/does-adaptive-thermogenesis-occur-after-weight-loss-in-adults-a-systematic-review/726FC60518DA67349B9C3EC1D75A7156
• InBody 270 Training Manual (official), on the use of the Cunningham equation to derive basal metabolic rate from lean body mass.
• NHS Health Check. https://www.nhs.uk/conditions/nhs-health-check/

{“@context”: “https://schema.org”, “@type”: “FAQPage”, “mainEntity”: [{“@type”: “Question”, “name”: “Does BTX do RMR testing?”, “acceptedAnswer”: {“@type”: “Answer”, “text”: “Not in house. We do not measure resting metabolic rate at the studio. We have a referral arrangement with a provider who does measure it, and we will point you there if a measured figure is worth having in your case. Everything after the test, reading it alongside your scans, training and food, is ours.”}}, {“@type”: “Question”, “name”: “Is the BMR number on my InBody sheet my resting metabolic rate?”, “acceptedAnswer”: {“@type”: “Answer”, “text”: “It is an estimate of it, not a measurement. The InBody 270 training manual states the device uses the Cunningham equation, a regression based on how much lean body mass you have. Your lean body mass was itself estimated from impedance, so it is an estimate built on an estimate. Useful as a starting point, not a measured calorie target.”}}, {“@type”: “Question”, “name”: “How much does an RMR test cost?”, “acceptedAnswer”: {“@type”: “Answer”, “text”: “We do not publish a figure. Since we refer rather than test, the fee is the testing provider’s rather than ours, and it varies with whether a test is sold on its own or inside a wider assessment. Ask on a call and we will tell you what we know.”}}, {“@type”: “Question”, “name”: “How is metabolic testing done?”, “acceptedAnswer”: {“@type”: “Answer”, “text”: “By indirect calorimetry. You rest quietly for 10 to 20 minutes, then breathe normally for about 10 while oxygen and carbon dioxide are measured, the first 5 minutes discarded. Food, alcohol, caffeine and nicotine must be controlled beforehand (Compher et al., 2006).”}}, {“@type”: “Question”, “name”: “What should I ask a provider before booking an RMR test?”, “acceptedAnswer”: {“@type”: “Answer”, “text”: “How long you rest before recording begins, whether the opening minutes are discarded, and what you are told to avoid beforehand. Those answers tell you whether you are buying a measurement or a printout.”}}, {“@type”: “Question”, “name”: “Will an RMR test show that my metabolism is damaged?”, “acceptedAnswer”: {“@type”: “Answer”, “text”: “No. Adaptation is real but typically 30 to 100 calories a day, and appears attenuated or absent after weight stabilisation (Nunes et al., 2022). The 499 calories figure comes from 14 people and is an outlier.”}}]}