DEXA scans, x-rays, and cancer

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There is what I consider to be an alarming trend of people running to get DEXA scans to get their bodyfat measured “accurately”, more about why I quote the world accurately later.   People tend to dismiss the radiation of a DEXA scan as being “less than a dental x-ray”, well, I even limit dental x-rays to a  bare minimum.  There is a difference too, an occasional dental x-ray is important for health because one needs healthy teeth to be able to eat a healthy diet full of fruits and vegetables and without a healthy diet, the rest of the body suffers.  A DEXA scan to measure bodyfat on the other hand has no such health benefit, its all cancer risk with no benefits – risk without reward.  Cumulative radiation exposure IS a big deal because our lives expose us to more and more radiation.  Radiation causes cancer, known fact. Small amounts add up.

Now, lets get to the accuracy of the DEXA scan which has every bodybuilder running to get tested.  Arnold gets a DEXA scan and his printout says that his bodyfat is 4.867523%, SO WHAT, the mirror is always right – who cares what a stupid little piece of paper says.  What is important is that you have a reliable method of determining if your bodyfat is slowly increasing or decreasing, not the exact bodyfat percentage.  Both a Measuring Your Fitness Progress and the skinfold caliper provide reliable and cheap methods of gauging your bodyfat changes from week to week – all without radiation and expense.

Now lets get to the “accuracy” of the DEXA scan.  I am an engineer and am fascinated by technology as much as the next guy and the DEXA scan is very cool but it has problems.  The software has to have algorithms to decide what its looking at inside the body – how to tell bone from muscle from fat.  The problem is that these algorithms are never perfect.  The bigger problem though is our old friend hydration.  We all know that our weight varies a LOT from day to day, as much as 10 pounds.  Its not that we are losing and gaining fat, its that we are retaining and shedding water based on water intake and salt intake.  Well it turns out that DEXA scans are thrown off by this water retention just as scales are.

If you truly need to know your bodyfat measurement to two decimal places, I would suggest plopping down a thousand dollar for real hydrostatic testing, NOT a body-pod.  If you just want to keep track of progress then use a $6 skinfold caliper or a $3 measuring tape.

The Mirror Is Always Right!

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