Bioelectrical Impedance To Measure Body Fat?

BIA from Weightology

Last week, my helper's cousin asked me for suggestions with regards to measuring her body fat levels. Her cousin was about to sign up with a personal trainer  and he wanted to measure her body fat levels before they started. Of course that came with a cost before the training even started.

Picture from Bodybuilding Wizard 

I told my helper the most accurate method would be hydrostatic underwater weighing (or underwater weighing) which was very dificult to do (pictured above). I only did it as a physiotherapy student while doing the exercise physiology module in year 1. Next best was using callipers to measure the sum of 7 skinfolds (pictured below).

However, my helper said the trainer suggested using bioelectrical impedance analysis (BIA) to measure her cousin's body fat levels.

Bioelectrical impedance is a popular way to measure body fat levels. It is also practical  as it takes a relatively short analysis time. It is not invasive at all and it is available commercially at an affordable cost.

BIA measures body composition based on the rate at which an electric currrent travels through your body. Body fat (adipose tissue) causes greater resistance (impedance) than lean mass (muscle) and slows the rate of electric current traveling through the body. Based on that rate and your height, gender and weight, your body fat levels, fat free mass etc are calculated.

However, BIA is not accurate at all for determining body fat levels. A recently (Aug 2024) published study showed that all 3 BIA devices tested significantly underestimated body fat levels.

28 firefighters were evaluated using 3 BIA devices. A multifrequency BIA hand-to-foot device, a single frequency BIA foot scale and a single frequency handheld BIA device. These were measured against dual x-ray absorptiometry (DEXA) for comparison (Jagim et al, 2024).

All 3 BIA devices significantly under measured body fat levels. Errors ranged between 4 to 5.5 percent when compared to the DEXA scans. Despite it's ease of use and practicability, BIA should not be used to assess body fat levels.

If you do or if your trainer insists on using BIA, bear in mind that they are not accurate, but you can still use them to track changes over time. 

Picture from Topendsports

I would suggest using the sum of 7 skinfolds if you want to track your body fat levels rather than BIA as it would be more accurate. The callipers are also not expensive. The following locations are commonly used. The abdomen, pectoral area, mid axilla, subscapular area, quadriceps, suprailiac area and the triceps.

There is more to health than your body fat percentage or weight. These measurements are not a reflection of your general well being. 

Reference

Jagim AR, Luedke J, Erickson JL et al (2024). Validation Of Bioelectrical Impedance Devices For The Determination Of Body Fat Percentage In Firefighters. J Strength Cond Resc. 38(8): e448-453. DOI: JSC.0000000000004809. PMID: 39072665