DEXA versus the rest (scales, InBody, skin folds etc)

Updated: Feb 6, 2019

Amie Cox, owner of Physique Science and Target Nutrition, explains the difference between BIA (biological impedance analysis) and DEXA and why there can be such a variance in results between the two different tools for measuring body composition.



If you’re monitoring your percentage body fat and muscle mass, chances are you are working VERY hard for your changes.


You’ve been sweating and sacrificing to lose a few kilograms of fat or gain a few of muscle.


So if you're anything like me, when you go to measure your results, you don’t want a scan result that is accurate to within a few kilos… you want your results accurate down to to the last gram!


Here are the facts from Amie....


A DEXA with us at Physique Science can identify changes in body fat and muscle mass of as little as 200-300g.

· This is much more accurate than InBody Scans (bioelectrical impedance), skinfold (aka calipers), underwater weighing, or Bodpod where errors in excess of 1-2kg can be common.

· I've seen clients scanned on InBody scales in their gym a few minutes apart and get a 5-8% difference in readings.

· Even with an ISAK accredited technician doing your skinfolds, the results are still "operator dependent" which means they will vary depending on the technician's technique and can even vary from day to day with the same technician. And they don't give you any information about muscle mass or bone health, they are just based on your surface fat.

· The percentage body fat results you are given with skinfolds and InBody are predicted (using data points and formulas), not directly measured like they are in DEXA.

· DEXA is the tool of choice for the Australian Institute of Sport (AIS) because it is the most accurate means of measuring your body composition.


I am a qualified sports dietitian... and there's a reason I bought a DEXA machine to work with my clients. And there's a reason the Lions, Firebirds, Broncos, Reds, and the Wallabies all use DEXA.


Amie explains the technical difference between BIA and DEXA…


A DEXA scanner is a type of x-ray machine so what you see on your scans is exactly what the x-rays detect as they pass through your body. This is based on the density of particles in your body and every gram is allocated as bone, fat mass, or fat free mass (your muscles and internal organs).


BIA scales are the scales you stand on at the gym and hold the handles to get a body fat reading. They are the most common way of testing body fat because they are portable, quick, and affordable. But just because something is the most common doesn’t necessarily make it accurate.


With BIA, an electrical current goes through your body and uses the information it gets to then predict the amount of bone and minerals, fat mass and lean mass you have. It doesn’t actually measure each component directly, but uses data and formulas to interpret your scan.


I’ve seen BIA scans performed consecutively on the same person and the difference in the results have been anywhere between 5 to 8%. I have also seen them provide exactly the same result from scan to scan... the issue I have is the inconsistency with BIA. Do you want to know with 100% certainty your result is accurate, or wonder how big or small the difference could be today?


Watch for calibration issues with BIA too


When BIA scales are brought out to your gym, they use a lot of different machines. If they use one machine for the initial scans and then a different machine for the follow-up scan, there will be a different calibration, so you need to be aware that can influence perceived changes in your results… it’s not actually your body that’s different, it’s how the machine is calibrated.


And yes, DEXA scan results can be inconsistent too…


Unless you follow the standard for best practice designed by scientists at the AIS like we do.


Read more about our prep here.


And if you have any other questions about the difference between BIA and DEXA, come in and have a chat or send us an email at info@physiquescience.com.au.


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