It is often referred to as the gold standard of body composition assessments. Dual Energy X-Ray Absorptiometry (DEXA) is the technology used to assess soft tissue and bone density. It is predominantly used to diagnose and monitor bone health issues such as osteoporosis but with the right application it can be used to assess body fat and muscle mass quite accurately. Most research studies use DEXA body composition scans as the choice of body composition analysis because of its accuracy.
I popped out to a practice in Durbanville recently to see it action and have a test done myself. Before I go on we all need to understand a few important points about body composition analysis. The main one being that none of them are 100% accurate, but some get closer than others. Most methods of assessment use a 2-compartment model dividng the body into fat mass and fat free mass. The error rate on these methods are quite high. DEXA uses a 3-compartment model meaning that not only can fat mass and fat-free mass be determined but fat free mass is separated from bone mass. This controls for those populations that have significant variations in bone mass and for those of us who blame the extra weight on being big boned!
The accuracy of DEXA body composition assessments may be 1-5% and errors are dependent on the software and hardware models, hydration status (as with most body composition measurement tools), sex, body mass and it does not appear to be a very good measure of small changes in body composition over short periods of time. If it is regular monitoring you are after something like skinfolds or ultrasound analysis might be better after your initial measurement, or even focusing rather on circumference losses in key areas. Using DEXA as a baseline test and then repeating once or twice a year is a good method to tie in to this.
My visit and scan was interesting. After finding out a little about the history of the practice and their testing procedure I was ushered to the scan room. The scan is fairly quick, it took about 5 minutes of lying still on a bed that looks fairly similar to this:
After the DEXA body composition scan is complete you will get a print out of the report, quick and easy. You can see an example of the report below. What is great is that you get a fat mass, bone mass and lean mass measurement not only as a total but according to body segments too. This can be valuable in setting your goals, monitoring and adjusting your training accordingly too.
I was very impressed and can see the value in using DEXA as another tool in the toolkit. I am incorporating this into my practice now and referring clients to have a scan done at baseline to improve the accuracy of what we do. If body composition improvements are what you are looking for you might as well find the best way to assess this before you start and put together a plan to monitor your changes. But keep in mind the limitations of it all and it is advisable to control as many factors as possible when having a scan done:
- try to have it done at the same time on every occasion (and same point in a menstrual cycle for females)
- follow the same hydration and urination practices before each test
- keep repeat tests 4-6 months apart
- use another reliable body composition assessment tool as a way to monitor short term changes
For more information or to request a referral for a DEXA body composition scan please get in touch.