Anthropometric and bioimpedance equations for fat and fat-free mass in Chilean children 7–9 years of age

Abstract

Assessing children‘s growth adequately is important due to the necessary prevention of adequate body composition, especially at prepubertal age. Simpler measurements such as anthropometry or bioimpedance, using equations validated in Caucasian children, have been demonstrated to overestimate or underestimated fat mass percentage (FM %) or fat-free mass (FFM) in Chilean children. In a sample of 424 children (198 boys and 226 girl) of seven to nine-year-old, three compartment methodology (3C model) was assessed, where total body water determined by deuterium dilution and body volume by air displacement plethysmography, in order to design and validate anthropometry and bioimpedance equations. The FM (%) equation specific for Chilean 7 to 9 years old, children were validated as 1.742*BMIZ) + (0.723* Triceps Skinfold) + (0.386 * Biceps Skinfolds) + 15.985, against 3C model (R2= 0.78) The new Fat-free mass (FFM) equation (kg) generated was (Log FFM = (0.018 *Age) + (0.005* Sex) + (0.006 * Weight) + (0.026 * Resistance) + 2.071), with a R2= 0.92. (Female=1 and 2=Male) The Bland Altman analysis shows a mean difference of 0.27 ± 3.5 for the FM% in the whole group as well as 0.004±0.94 kg is the mean difference for the BIA-FFM (kg) equation. The limits of agreement for the body fat (%) are C1 =6.82 and C2= -6.85. Meanwhile the C1 for the fat-free mass is 1.79 and C2 is -1.87. The realization of the equations consider a cross-validation to estimate fat and fat-free mass using a three compartment reference methods The new equations for FM (%) and FFM (kg) in Chilean children will provide a simple and valid tool for the assessment of body composition in cohort studies or to assess the impact of nutritional programs or public policies.

The Body Adiposity Index is not applicable to the Brazilian adult population

“…The low cost and ease of use may explain the number of studies that have been carried out to propose anthropometric mathematical models for estimating body composition in different groups or to validate existing ones ( 30 – 35 ). However, most of these equations were proposed to meet the specificities of the group under study, such as breast-feeding children ( 30 ), children ( 34 ), adolescent athletes ( 33 ), healthy adults ( 31 ), or those with chronic diseases ( 32 ) and elite athletes ( 35 ), among many others, which cannot be generalized to groups other than the population of origin.…”

“…The 4C model is the most appropriate reference method to assess FM and FFM at the molecular level ( 5 ). However, due to the complexity of the technique ( 42 ), the use of DXA to derive anthropometric equations has been widely accepted ( 7 , 34 , 36 , 37 ). It is noteworthy that the new equations are only useful for Brazilian adults with similar characteristics.…”