Standing-position BIA or supine BIA? A new answer to an old question

Which method to use for a fast assessment of body fat percentage?
K Zdešar Kotnik, T Robič and P Golja
Physiol Meas. 2015 Jul; 36(7):1453-68. doi: 10.1088/0967-3334/36/7/1453

In this study, researchers from the University of Ljubljana (Slovenia) compared fat estimates obtained with hand-to-leg BIA and leg-to-leg BIA, in standing and supine positions, to determine which BIA method is best for the fast assessment of body fat. Skinfold thickness measurements were used as the reference standard. An STA/BIA device (Akern) with Bodygram software was used to assess hand-to-leg measurements, while a TBS-215 device (Tanita) was used for leg-to-leg measurements.

The study found that body posture induced changes in impedance values large enough to significantly affect body fat estimates. The authors concluded that “compared to the reference … method, hand-to-leg BIA provides better estimates of body fat percentage than leg-to-leg BIA.” They also concluded by recommending methodological standardization and suggesting the use of different approaches to body composition analysis by means of direct BIA measurements.

Akern reminds readers that our company has endorsed the use of direct BIA measures since 1995 and has promoted standardization of the BIA technique since 2007.

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BIA is more accurate than BMI for estimating fat mass

How to estimate fat mass in overweight and obese subjects”
LM Donini, E Poggiogalle, V del Balzo, C Lubrano, M Faliva, A Opizzi, S Perna, A Pinto and M Rondanelli
Int J Endocrinol. 2013; 2013: 285680. doi: 10.1155/2013/285680

Body mass index (BMI) is a quick and simple tool for calculating body composition, but it is unable to distinguish fat mass from lean body mass and therefore has little value in the clinical assessment of overweight and obese patients. Fat mass can be accurately assessed using dual-energy X-ray absorptiometry (DXA), but this method is not always available or feasible. Researchers in Italy therefore tested a panel of different methods for estimating fat mass, including 13 anthropometric variables, 10 bioimpedance analysis (BIA) variables, and 16 biochemical variables. These results were then compared to fat mass from DXA, considered the reference value.

This two-center study (Pavia and Roma) enrolled 103 healthy adults (74 women and 29 men) with a BMI between 25 and 35 kg/m2. Patients had blood sampled and underwent body composition measurements by DXA, BIA and anthropometry in a fasting state. Whole-body impedance was measured with a single-frequency 50 kHz analyzer (STA-BIA, Akern). Obesity was defined as a BMI >30 kg/m2 or, for DXA and BIA, as a fat mass ≥25% for men and ≥35% for women.

According to the reference method DXA, the study group comprised 101 obese and 2 nonobese persons. According to BMI there were 55 obese and 48 nonobese persons, while according to BIA there were 85 obese and 17 nonobese persons. BMI and BIA both had 100% specificity, but the sensitivity of BMI was only 48% while that for BIA was 85% in detecting obesity. No laboratory test result was better correlated with DXA fat mass and, among the anthropometric variables examined, only hip circumference was slightly better than BMI (but less than BIA).

This study confirms that BMI is not a reliable indicator of obesity. The authors suggested that, when DXA is not available or feasible, body composition is better assessed with BIA than BMI. They “hypothesize that the use of BIA in combination with other biomarkers (leptin levels in particular) could be very useful in defining the clinical features of the obese patient in order to better address the therapeutic and rehabilitative approaches.”

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