Do X-Rays Work Better for Body Fat Testing? Slovenija

What about other body fat tests, like DEXA scans? Do they work any better?

DEXA, short for dual-energy X-ray absorptiometry, does a reasonable job at estimating group averages. But, it’s not as good at tracking individual changes in body fat and muscle mass over time.

Why is that? DEXA might overestimate body fat percentage in half your group by five percent, and underestimate it in the other half by five percent. When looking at the group results, the average error size is zero. But the individual results are way out.

The fact that a body fat test does a good job at estimating group averages doesn’t necessarily mean that it’s equally as good at tracking individual progress over time. When Purdue University researchers compared DEXA with the gold-standard 4-compartment model, the results were a mixed bag. In some individuals, the results were a close match. But in others, they were way out.

One subject gained five percent body fat according to the 4-compartment model, but DEXA showed that it had dropped by five percent. Another lost nearly 10 percent body fat according to the 4-compartment model, but DEXA showed only a three percent drop.

And DEXA isn’t cheap, with a single scan costing upwards of $100. If you go back for a second scan after a few months, that’s another $100. That’s a lot of money to spend if the results aren’t telling you anything useful.

Some argue that doing back-to-back DEXA scans “proves” they’re accurate. That is, if you get yourself scanned, then return to the same machine the next day and get another scan, the results will be almost identical. However, this doesn’t tell you that the scan has done a decent job of estimating your body composition. All it tells you is how close the estimates are when repeated measurements are made. It doesn’t tell you how accurate those estimates are in the first place.

The technology involved in body fat testing still has some catching up to do. Commercial body fat testing devices are not accurate enough for you to use the information to make better decisions about what to eat and how to train. Put your faith in only the results of a body fat test, and you might end up thinking that your diet and training program isn’t working, when really it is—or that it is working when it isn’t.

Original in Men’s Health https://www.menshealth.com/fitness/a26382163/body-fat-tests/