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Why DEXA scan prep matters... no matter what the others say

If you’re monitoring your percentage body fat and muscle mass, you are working hard to achieve some changes. You’ve been sweating and sacrificing to lose a few kilograms of fat or gain a few of muscle.

So you don’t want a scan result that is accurate to within a few kilos… you want it down to the gram!

No matter what anyone tells you, other tools to measure your fat and muscle like…

· underwater weighing

· Bodpod

· bioelectrical impedance and

· skinfold (calipers)

… are only accurate to within 1-2kg… and unfortunately, it’s often much worse! Even a DEXA scan performed by a technician who doesn’t have the right training can also have an accuracy range of 1-2kg!

But an appointment with us at Physique Science can identify changes in body fat and muscle mass of as little as 200-300g… and we’ll tell you straight up that’s as tight as it gets for any technique.

Why can we be so confident in our accuracy?

We can get our range so tight because we specialise in using DEXA to measure body composition and we recommend a very specific prep for you to follow before your scan.

Our prep recommendations might all sound a bit geeky but this technique was developed on the back of 15 years research. And we recommend it because it will get you the most accurate result that can be compared to future scans.

The prep’s not hard… When you book in, we’ll send you an email with our recommendations for what to eat and drink in the lead up to your scan including overnight fasting.

Here’s what we recommend …. and why!

Come for your scan fasted… that means nothing to eat or drink after dinner the night before and empty your bladder prior to your scan.


Any food or fluid ingested before your scan is detected by the DEXA scanner and represents part of your body mass at the time of your scan which skews the result slightly.

We explain everywhere that DEXA measures three things… bone, fat and fat-free mass. Fat-free mass is also called lean soft tissue which includes your muscles and everything else including your internal organs, water, blood vessels etc.

The DEXA scanner recognises fat and bone specifically because they have a very defined, consistent appearance… and everything else is assigned to your fat-free mass. That means if you’ve got lots of extra food or water in your tummy, it will be added to your lean tissue reading and will mean you end up with an over-estimation of your muscle mass. No food or water on-board, no problem!

If you really can’t do this, don’t stress we have a solution which we talk about at the very end of this post*.

But eat well the day before with a sensible amount of quality carbs (we’ll explain why a bit more below when we get a bit geeky about glycogen)

Be well hydrated for your scan…. I know we just said don’t drink anything in the morning before your scan but if you drink 1-2 glasses of water with each meal/snack the day before, you’ll be hydrated enough the morning of your scan.

And finally, don’t train in the morning before your scan.

So this is where we have to get a bit ‘science-nerd’ but it’s all about having your muscle glycogen stores full.

What the hell does that mean? Well, to keep it as simple as we can, changes in your muscle energy reserves (glycogen) impact on the measurement of muscle mass. If you want to know more about how and why, ask when you come for your scan.

What happens if you do train or don’t eat the carbs?

Let’s say you have really pulled back on the carbs in the weeks before your appointment or had heavy training the day before, then you’ll find your muscles are a bit glycogen depleted. That means the measure of muscle mass could be lower by upwards of 500g or in extreme cases, as much as 1kg lower.

One more thing and this is EASY…

Wear clothes that don’t contain any metal, including zips, clips etc. We have disposable gowns available if needed. Hot tip ladies… those Lorna Jane tops more often than not have a little metal LJ dangly thing somewhere so take a little extra look.

These factors are not unique to our scanner – they affect every DEXA scanner (and all other methods of assessing your body fat and muscle mass) no matter what others may say. But we understand them and plan for them because we want you to get the most accurate result.

Following our prep recommendations will make a difference.

If you want confidence in your results, this is the best way to achieve it. And the good news is… we open from 5am so you don’t have to go hungry for long and you might still squeeze in a workout after your scan and before work or the day takes over.

*If you can’t avoid eating or drinking before your scan – we know life doesn’t always pan out the way we want it to – we recommend you make a note of what you ate and drank prior to your scan and do the exact same thing before your follow-up scans. A cup of coffee and a bowl of oats will be interpreted the same way every time so if you do have to eat and drink your results will still be comparable if you want to track changes in fat and muscle over time.

Got questions? Drop us an email at

But most importantly… book your scan NOW and find out your DEXA health.

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