Measuring body fat percentage: It's an accuracy thing

    Comparing DEXA versus Bod Pod for people with different BMI.

    There are several different ways to determine your body fat percentage, and with summer quickly approaching, we’ve been getting a lot of questions about the most accurate method.

    Body fat measurement techniques range from cheap and inaccurate, to expensive and precise. Though the ideal method is accurate, repeatable, and cheap, no such method actually exists. The two most accurate methods, hydrostatic weighing and dual-energy X-ray absorptiometry (DEXA, which is synonymous with DXA) are too expensive for the average person to use frequently.

    A recent study compared the accuracy of DEXA and a ‘bod pod,’ or air displacement plethysmograph, a device that determines body fat based on how much air is displaced when a person gets in the pod. This is conceptually similar to hydrostatic weighing, except it uses air, not water.

    This study examined three groups of participants: people with a below average BMI (18.5), higher than average (25 or greater), and a middle group with BMI between 18.5 and 24.99. Researchers performed two body fat measurement tests on each participant, six hours apart.

    Underweight people measured with DEXA were determined to have 8.82% body fat, while the bod pod measured 16.15-16.16% body fat. The bod pod overestimated body fat by an average of 6.79-6.84%, when compared to DEXA measurements. The largest individual difference was 13.2%, which was observed when an individual with a very low body fat percentage was measured.

    People with a healthy BMI had 20% body fat, as calculated by DEXA, compared to 21.96-22.45% according to the bod pod. Average weight individuals had slightly higher body fat percentage when measured by the pod pod, compared to DEXA.

    Overweight individuals reported an average body fat of 34.38% when measured by DEXA, compared to 31.64-32.93% from bod pod measurements. Bod pod readings were slight underestimations compared to DEXA.

    The researchers concluded that the bod pod was more accurate when testing people closer to a healthy BMI. The bod pod was less accurate than DEXA when it came to measuring very lean individuals. People with low body fat percentages were much more likely to get a higher reading from the bod pod, and people with higher body fat percentages were more likely to see a lower readout.

    This finding is important for both research and self-tracking. The more accurate scientists can be when tracking data and people’s health, the more they know about potentially life-saving therapies and medicines. People who get their body fat tested (whether bodybuilders or just people looking to track their weight loss) sometimes equate the bod pod to DEXA in terms of accuracy, but they should be aware that measurements between the two can vary considerably.

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