The Jury is Still Out
When it comes to tracking changes in our bodies, many of us still rely on ‘old faithful,’ (a.k.a. the bathroom scale). The problem with this is that weight is a poor substitute for what we actually want to know: how much fat we’re carrying around and how our bodies are changing.
In recent years, a number of different methods have burst onto the scene, all claiming to accurately measure body fat. But how accurate are these methods really? Are they one and the same?
Body Fat Calculations Explained
First, let’s set the stage. Our bodies are more than just “fat” and “not fat”. Our bodies can be divided into fat, water, bone, soft tissue, and protein (and no, not the whey kind you see people chugging at the gym). Because no technologies exist that can directly measure all of these components in one shot, we often rely on our knowledge of their properties – which differ relatively little from person to person. So, all commonly used methods directly measure some parts of our bodies and then combine the measured values with the inferred values to come up with the best estimate for your body fat percentage.
In developing and refining Naked's algorithm for measuring body fat, we’ve come across some surprising findings. Our employees and beta testers alike have been receiving regular dunk tank tests (a volumetric method used to determine body fat) and DXAs (an X-Ray method to do the same) and we've observed drastic differences between the two methods.
One of our beta testers, Deepika, took a DXA and dunk tank test on the same day, one immediately following the other. DXA reported Deepika’s body fat as 3 percent higher than dunk tank, with a full 4-pound discrepancy in lean mass!
Deepika is not the only one to have this experience. Another of our beta testers, JD – a multi-time Ironman – saw a large discrepancy. From hydrostatic to DXA, his body fat estimate was 5% lower, while his lean mass was 8 pounds higher. Note that these scans were taken minutes apart!
We’ve seen results in the opposite direction, too. Jennie, a beta tester and avid at-home exerciser, was 4% higher in body fat as measured by DXA versus dunk tank. That’s a big change for such a slender person.
The more BF% results we’ve come across, the more we’re left scratching our heads. Why are these measurements consistent for some people, but wildly different for others? Why are DXA results telling elite athletes that they’re overweight? What are the sources of error? And how does Naked fit in?
Over the next few weeks, we’ll be introducing the different methods used to assess body fat. We’ll give you the scoop on what the different tests do well and what they do poorly – and hopefully give you some interesting tidbits you can use to rivet strangers at your next cocktail party!
This article was written by Dr. Sam Winter, Naked's Research Scientist.