I Tried The Machine That Tests Your Metabolism

Calories in, calories out. Weight loss is ‘simple’ – except that it isn’t.

As far as ‘calories out’ is concerned, we are told to move more to use up more energy. But how much energy you burn doing the same activity as another person will depend on your body composition, weight and the speed of your metabolism, the complex collection of chemical reactions going on inside of you.

Whilst an online calculator can estimate your Resting Metabolic Rate  (RMR) or Today Daily Energy Expenditure (TDEE),everyone’s metabolism is unique. For most of the population, your metabolism will fall somewhere around average so an online calculator might be all you need to help you plan your nutrition to manage your weight.

But what if you think you are a metabolic freak with a way above or below average metabolism? Such people do exist and if you are doing everything ‘right’ but still not meeting your training / aesthetic goals it might be something to consider.

Side note – if you think your metabolism is ‘broken’ due to chronic dieting or an eating disorder don’t fear! You might want to read this article for reassurance. It cites a study showing that anorexics recovered for two years had the equal BMRs to those who never had an eating disorder. Bottom line – your body will bounce back into homeostasis if you take proper care of it nutritionally.


Of course not everyone struggling to lose weight has ‘metabolic damage’. They may be miscounting calories or overestimating energy burned through exercise. But that isn’t to say that you can’t be one of those people to have a slower-than-average metabolic rate. If you want to find out for sure there is only one thing to do – take a RMR test!

Unfortunately the service costs about 100 pounds on average in the UK but if your weight management is causing you considerable stress or impacting your ability to function and enjoy life the money could be worth the investment in your health.


The process is really easy. All I was told to do was fast for at least 4 hours before on the day, avoid exercise 48 hours before, try not to get stressed, no smoking and turn up!

The test itself is simply a measure of how much carbon dioxide and oxygen you breathe in and out which can be used to calculate how much energy your body is burning. You place a mask over your face attached to a breathing tube which is linked up to computer software and lie back and chill out for 15-20 minutes like the dude below:

The only time naps will ever be acceptable in the gym!

It did feel a bit weird having a tight mask strapped to my head for the first few minutes but when once I got used to the sensation it was actually quite relaxing – I probably would have fallen asleep if it wasn’t for the ticking and beeping of the machine!

Afterwards the software generates a graph and the straightest line measuring the O2/CO2 levels is used to calculate an accurate estimate of how many calories your body burns at rest over 24 hours. Letting the machine run for 15-20 minutes ensures you are relaxed enough that the machine is recording a true measure of your body at rest.

As for my result? My hunch was right – I did have a thrifty metabolism. But luckily for me it wasn’t exceedingly low – about 150 calories less than was expected for my weight and height – nothing I can’t combat with mindful nutrition and working on building some lean mass to increase my RMR over time. Apparently at my coach Mark’s practice he regularly has clients with an RMR of 200-300 calories below average and the lowest ever RMR he ever saw was around 600 calories for a client with an eating disorder.

Metabolic adaptation does happen when you eat less calories than you need, particularly if you drop calories very low. If you have a slow metabolism because you haven’t been eating enough then slowly upping your calories by 50-100 each week until you reach a normal intake, called reverse dieting is a recommended method to increase your metabolism without gaining excess fat. If you want to learn more about reverse dieting check out the bodybuilding.com  reverse dieting guide here. (Of course if you have an eating disorder please speak to your physician about the best course of action.)

Either way, if you take an RMR test you will know for sure whether you are eating the right amount to give your body the nutrition it needs and to facilitate your weight and/or fitness goals!

I booked my test here with an absolutely lovely trainer called Mark Clarke and it cost me £74.99 – not cheap but it was money well spent in my opinion! You can also book a range of other services including a customised nutrition plan and an exercise test (VO2 max) which might be helpful if you are an athlete looking to improve performance/ maximise fat burning as it shows you at which heart rate you burn the most fat compared to carbs. Also the RMR test  does also tell you your ratio of carbs:fat you burn at rest you can see how keto-adapted your body is!

I would definitely love to go back in the future to see how my scores change – watch this space!



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