Development and cross-validation of predictive equations for fat-free mass estimation by bioelectrical impedance analysis in Brazilian subjects with overweight and obesity

• Published in: Frontiers in nutrition (Lausanne) 2025-01, Vol.12, p.1499752
• Main Authors: Masset, Kalina Veruska Da Silva Bezerra, Silva, Analiza M, Ferrari, Gerson, Cabral, Breno Guilherme De Araújo Tinoco, Dantas, Paulo Moreira Silva, Da Costa, Roberto Fernandes
• Format: Article
• Language: English
• Subjects: absorptiometry; adults; body composition; mathematical models; Nutrition; resistance index
• ISSN: 2296-861X; 2296-861X
• DOI: 10.3389/fnut.2025.1499752

Obesity is a public health problem worldwide, and body composition assessment is a very important diagnostic tool. Bioelectrical Impedance Analysis (BIA) is a fast, non-invasive, relatively low-cost, and user-friendly technique; however, to obtain greater validity of the estimates, the predictive equations used must be population specific. Thus, the objectives of this study were: (1) to test the validity of four BIA equations used for fat-free mass (FFM) estimation and one model for fat mass (FM) estimation in adults with overweight or obesity; (2) develop and cross-validate new equations to estimate FFM to adults with overweight or obesity, and specific for those with obesity. The non-probabilistic sample included 269 individuals, 53.2% with overweight and 46.8% with obesity, aged 18-79 years, randomly divided into two groups: development ( = 178) and cross-validation ( = 91), stratified by sex and classification as overweight or obese. The criterion technique was dual-energy-x-ray absorptiometry (DXA), whereas a tetrapolar single-frequency BIA equipment was used as the alternative method. Paired t-test, multiple regression, concordance correlation coefficient, and Bland-Altman analysis were used. Most existing equations were not valid and new equations were derived: (1) for individuals with overweight or obesity: CCC = 0.982; r = 0.95; standard error of estimate (SEE) = 2.50 kg; limits of agreement (LOA) = -5.0 to 4.8; and (2) specific for individuals with obesity: CCC = 0.968; r = 0.94; SEE = 2.53 kg; LOA = -5.3 to 5.2. No FFM differences were observed between the new models and the reference method ( > 0.05). The new proposed models provide valid options to estimate FFM in an adult population with overweight/obesity.