Associations of age and body mass index with hydration and density of fat-free mass from 4 to 22 years

Abstract

Background: Most body composition techniques assume constant properties of Fat Free Mass (FFM) (hydration and density) regardless of nutritional status, which may lead to biased values. Aim: To evaluate the interactive associations of age and Body Mass Index (BMI) with hydration and density of FFM. Methods: Data from subjects aged between 4 and 22 years old from several studies conducted in London, UK were assessed. Hydration (H FFM) and density (D FFM) of FFM obtained from 4 component model in 936 and 905 individuals, respectively, were assessed. BMI was converted in z-scores, and categorised into five groups using z-score cutoffs (thin, normal weight, overweight, obese and severely obese). Linear regression models for H FFM and D FFM were developed using age, sex and BMI group as predictors. Results: Nearly 30% of the variability in H FFM was explained by models including age and BMI groups, showing increasing H FFM values in heavier BMI groups. On the other hand, ∼40% of variability of the D FFM was explained by age, sex and BMI groups, with D FFM values decreasing in association with higher BMI groups. Conclusion: Nutritional status should be considered when assessing body composition using two-component methods, and reference data for H FFM and D FFM is needed to higher BMI groups to avoid bias. Further research is needed to explain intraindividual variability of FFM properties.

The Importance of Hydration in Body Composition Assessment in Children Aged 6-16 Years

“…The variation in HFFM is in agreement with a recent study by Gutiérrez-Marin et al . who went on to determine that approximately 30 % of the variability in HFFM can be attributed to age and BMI ( 26 ). This supports the argument that a linear assumption of 0.73 across children and adults is inappropriate.…”

Validation of bioelectrical impedance analysis for body composition assessment in children with obesity aged 8-14y

“…ADP (nowadays performed by a BODPOD device) is accurate, reliable and precise [41], but it is expensive, needs to be placed in a room with specific conditions and requires an exhaustive preparation before each use. We recently published a methodological approach to reduce the bias produced by the ADP by assuming a constant hydration and density of FFM in children with obesity [11,28]. Thus, this was the method used in the present work to generate a new equation to estimate body composition from BIA in children with obesity.…”

“…FM was used as a dependent variable in a predictive model to create a new equation was obtained using body volume from ADP and density of fat-free mass (predicted) following the procedure detailed below (to avoid the bias that could be produced by changes in hydration and density in obesity). D FFM was calculated using the following predictive equation [11]:…”

“…However, when considering a special population such as children with obesity, equations for the normal weight population may not be appropriate [14,23]. One of the most important key points is that FFM in children with obesity has different properties (hydration and density) than normal weight children [11]. Therefore, if bioelectrical impedance equations are obtained by comparison to techniques that also assume a constant hydration of FFM, as in DXA, these predictive equations will always be adding bias to the analysis of children with obesity.…”

Macroanatomical and Topographical Features of Body’s Adipose Component Content in Girls

“…Поэтому при оценке физического и пищевого статусов здорового и больного человека состоянию этого показателя всегда уделяется особое внимание [7,9,13]. Уровень жировой составляющей тела подвержен гендерной, конституциональной и индивидуальной изменчивости, а также влиянию этнических факторов и условий места проживания [2,4,6,13,15]. Нет сомнений в необходимости постоянной ревизии стандартов физического развития, включающих и количественное представительство жировой составляющей тела.…”