One of the key services which My Vital Metrics offers is the DEXA Scan. DEXA, (or sometimes just DXA), Dual-energy X-Ray Absorbiometry, is one of the gold standards in measuring body composition. In this article we will walk through the technology of DEXA by itself, and give you some sense of how it works, and why you might consider it.


DEXA – The Machine

DEXA was a machine originally developed to measure bone density, to diagnose conditions like osteoporosis, and within the NHS, and in health services all over the world, it is still the primary tool for doing this. However, DEXA machine also is great as measuring body composition. In this context it is used in medical setting to measure levels of muscle wastage (sarcopenia) owing to disease states or poor lifestyle. Using it on healthy people as part of body recomposition programmes has not been widespread in the UK, but is a recognised use and has been much more common to date in the US and Australia.
The machine divides up the body into three types of tissue. In body composition science, these are called compartments, so the DEXA is referred to as a 3 compartment model. The three compartments DEXA measures are Bone minerals, fat, and everything else that isn’t one of those two.
The ‘Dual-energy’ part of the name means that DEXA has two different X-Ray beams which pass through your body. A receiver on the other side will collect what is remaining of the X-Ray beam, measures it, and is able to make some calculations. One of the X-Rays is configured to pass right through soft tissue, but is absorbed by bone mineral. The greater the amount of bone mineral, the more of it is absorbed, and so you can get a calculation at that point through the body, how much bone mineral there is. 
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The second ray is a different energy beam which is absorbed in different quantities by fat, and by everything that is not fat (fat free mass – or FFM). This will include your organs, blood vessels, blood, muscle etc. When you put the two sets of figures together you can tell, for each pixel of the image how much bone is in there, how much fat, and how much of everything else. It’s like taking an image of a pixel sized core-sample – without actually taking out the sample. When you then add  up all the different compositions for all the pixels in the image, you get an overall measurement of your bone, fat, and lean tissue masses.
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What does it give you in the end

One of the great things about DEXA is that, as an imaging technique, it can not only tell you how much fat, and how much muscle – but where these are. If we take muscle – knowing that you have 400g more muscle in your left arm than your right might point you to some imbalances in the way you are training, or might reflect the  affects of an old injury on one side. 


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Location of fat is becoming increasingly important as well. Recent studies have started to find that the fat which sits in our abdomen, around the liver, kidneys and the bowel shows a higher risk factor for cardiac and metabolic diseases than the fat you are able to measure below the skin. Our DEXA machine can give you an indication if this is a problem in your case.
Further, the fat which you deposit around your hips and thighs (sometimes called gynoid fat) compared to fat deposited around your midsection (sometimes called android fat) can give some indication of whether a sex hormone imbalance might be implicated.
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On top of this, DEXA gives a hugely accurate value in overall body fat %. The accuracy of the result can be affected by issues of vast changes to hydration, so heading to your DEXA scan after an intense HIIT session or Spin class might not be a great idea. It would also be ideal to try to standardise the time of day you take your scans, and know exactly what you’ve eaten and drunk that day to get the best scan-to-scan consistency.


What about the Radiation?

Yep, DEXA is still an X-Ray machine, and so will give you a very small dose of radiation. The amount of radiation (<10µSV) is tiny however. It is roughly equivalent to a single day’s background radiation, or taking a 1 hour flight, or eating about 100g of Brazil nuts (yes, really!). It is about 10% of the radiation you’d get from a full chest X-Ray. Nevertheless it is radiation, and Public health England has given us guidelines on the number of scans you can take in a year.
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In Summary

DEXA has actually been around for 30 years. A recent article reviewed the advances in this technology over that time and highlighted the unique place and value DEXA has in sports and fitness assessments. The biggest challenge it noted, was getting people access to the scans, a problem we at MVM are very much trying to address.
Questions or comments about the article? Post them below! 
My Vital Metrics has a DEXA Scanning service which will be opening in London in January 2020. If you’d like to find out more, be added to our mailing list below. We’ll be posting some launch specials for DEXA and our other services.