Background/ObjectiveThe Relative Fat Mass (RFM) is an alternative index to body mass index (BMI) for estimating whole body fat percentage (BF%). Our aims were to determine the accuracy of the RFM for 1) identifying individuals with elevated BF% and, 2) estimating the BF% compared to Dual-energy X-ray absorptiometry (DXA) in a Chilean adult population.Subjects/MethodsBody composition was assessed by DXA in 270 healthy participants (125 women/145 men). Anthropometric measurements were assessed to calculate RFM and BMI. Receiver operating characteristic (ROC) curves were obtained to assess the sensitivity and specificity of both, RFM and BMI. Bland-Altman analysis between BF% measured by DXA vs. predicted BF% derived from RFM was performed to assess validity. Pearson<acute accent>s correlation coefficients to analyze the association between BMI, RFM and DXA were also calculated.ResultsFor RFM, the cut-off for elevated BF% was >= 22.7% for men and >= 32.4% for women and for BMI was >= 24.4 kg/m2 for men and >= 24.1 kg/m2 for women. The area under the ROC curve between RFM and BMI was not significantly different in men (0.970 vs. 0.959; p = 0.420) and women (0.946 vs. 0.942, p = 0.750). The Bland-Altman analysis showed that the estimation bias is more pronounced in men than in women.ConclusionRFM is an accurate tool for identifying individuals with elevated BF%, although it was not as accurate as DXA for estimating the BF%. RFM may be an alternative method useful in primary care to select individuals for lifestyle counseling and in research to select patients for epidemiological studies.