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.”