Relative fat mass is a better tool to diagnose high adiposity when compared to body mass index in young male adults: A cross-section study

Abstract

Background and aim: Relative fat mass (RFM) is a new method to estimate whole-body fat percentage in adults using an anthropometric linear equation. We aimed to assess the association between RFM and body fat (BF), evaluated by dual x-ray absorptiometry (DXA) or bioelectrical impedance (BIA), in young male adults.

Methods: Eighty-one young males were assessed for BF fat and free fat mass (by BIA and DXA), waist circumference. BMI and RFM were then calculated from data collected from the subjects. The agreement between BMI and RFM or BIA/DXA was assessed by Pearson's Correlation and Kappa index. Univariate and multivariate linear regression were applied.

Results: Analyzing all the participants together, the correlation between RFM and DXA (r_DXA = 0.90) or RFM and BIA (r_BIA = 0.88) were slightly higher than the correlation between BMI and DXA (r_DXA = 0.79) or BMI and BIA (r_BIA: 0.82). When analyzed by BF, low BF (LBF) individuals showed a much higher correlation with RFM (r_DXA = 0.58; r_BIA = 0.73) than BMI (r_DXA = 0.24; r_BIA: 0.46). However, subjects with excess BF (EBF) presented similar correlations when comparing RFM (r_DXA = 0.80; r_BIA = 0.64) and BMI (r_DXA = 0.78; r_BIA = 0.64). In general, RFM presented a higher strength of agreement with DXA and BIA (k_DXA = 0.75; k_BIA = 0.67) than BMI (k_DXA = 0.63; k_BIA = 0.60). Multivariable linear regression also revealed high associations between RFM and DXA or RFM and BIA (r²_DXA = 0.85; r²_BIA = 0.81).

Conclusion: Our findings suggest that RFM shows a good correlation and association with BF measured by DXA and BIA in young male adults. Furthermore, RFM seems to be better correlated to BF in LBF individuals when compared to BMI. Therefore, further studies investigating RFM as a tool to assess BF and obesity are motivated.

Keywords: Adiposity; Anthropometric indicators; Body composition; Fat mass; RFM.