Development and validation of anthropometric predictive equations that estimate the total body water and fat-free mass in Tunisian adults

OBJECTIVE: To develop and validate equations that estimate total body water (TBW) and fat-free mass (FFM) in adults using anthropometric measurements.METHODS: A cross-sectional study was conducted among 178 adults (77 men and 101 women; aged 18-59 years). Participants were distributed by sex and age groups, and then randomly assigned to equal two groups; the development (n = 89) and the validation (n = 89). The anthropometric measurements included height and weight. The deuterium dilution technique (DDT) estimated TBW and FFM. Linear regression models were used with the TBW and FFM as the dependent variable, and height and weight as the independent variables. Cross-validation was performed by Bland and Altman plot, and the new anthropometric equations were developed.RESULTS: In the validation sample, the developed equations had high R-2 of 94.4 for both TBW and FFM in all age groups, and low standard errors (RMSE: 1.80 kg for TBW and 2.44 kg for FFM). The pure error was 2.03 for the TBW equation and 2.71 for the FFM equation. The Bland-Altman plot illustrated the good level of concordance between the TBW and FFM predicted by the new equations as determined by DDT. The following developed equations showed a better agreement with the DDT: TBW(kg) = 0.0758 + 0.2979 x weight + 0.1234 x height 0.0416 x age 8.7113 x sex(men = 0, women = 1); FFM(kg) = -0.4475 + 0.4055 x weight + 0.1691 x height 0.0459 x age 11.7752 x sex(men = 0, women = 1).CONCLUSION: In this study, we developed and validated prediction equations for the estimation of TBW and FFM from DDT in healthy adult Tunisian population. The newly anthropometric prediction equations seem to be the most accurate for Tunisian adult.