Body composition assessment in pediatric patients. Validation of new methods of body composition measurements in obese children
- Autores: Desirée Gutiérrez Marín
- Directores de la Tesis: Verónica Luque Moreno (dir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Luis Moreno Aznar (presid.), Josep Ribalta Vives (secret.), Dariusz Gruszfeld (voc.)
- Programa de doctorado: Programa de Doctorado en Biomedicina por la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Background: Childhood obesity is one of the most important health problems at global level and it has reached epidemic levels at both developed and developing countries around the world. Obesity is defined as an excess of fat in the body but it is usually diagnosed by methods which cannot actually measure or estimate the adipose tissue of the body, i.e. body mass index (BMI). There are many existing techniques which can differentiate body compartments in vivo and then, fat can be estimated with a relative high level of accuracy, i.e. dual energy X-ray absorptiometry (DXA), air-displacement plethysmography (ADP), isotopic dilutions, multi-componentt models, among others. The gold standard method to assess body composition in vivo is the four-component model. However, techniques have some limitations, and mainly, all of them are expensive and implausible for clinical practice. Bioelectrical impedance analysis (BIA) has been proposed as a suitable technique to assess body composition in a wide range of populations, including obese children. However, there are research evidences that showed a poor accuracy and precision of BIA body composition assessments in this population.
Aim: To improve the accuracy and precision of the body composition assessment techniques in obese children and adolescents to make them suitable to clinical practice.
Methods: Three studies have been done to perform this thesis: • Study 1: This was a cross-sectional observational study to describe the fat-free mass (FFM) properties from childhood to young adulthood considering the total body mass. A British cohort of 1014 measurements from participants aged 4 to 22 years old with no BMI restriction was analysed. The whole sample was classified by five BMI z-scores groups (thinness, normal weight, overweight, obese and severely obese) according to WHO classification. Body composition (fat mass (FM) and FFM) was assessed by the four-component model and then, the fat-free mass (FFM) properties, hydration and density of the FFM, were calculated. The hydration and the density of the FFM were then compared between the five BMI groups. A linear regression analysis was then performed to develop different predictive models for hydration and density of the FFM calculations.
• Study 2: This was a cross-sectional validation study, secondary to a randomized clustered clinical trial (OBEMAT2.0). The baseline body composition data of 66 participants enrolled in the OBEMAT2.0 clinical trial was used. We obtained ADP body composition measurements (FM, FFM and body volume) with a BOD POD device. The density of the FFM was calculated using the equation developed in study 1. These calculations where then used together with body volume obtained from ADP to assess FM and FFM. The four-component model was calculated with FM Fuller’s equation. DXA, ADP and deuterium dilution where performed to obtain bone mineral content, body volume and total body water respectively to perform the four-component calculation. The agreement of the FM and FFM calculated measurements from density of the FFM and ADP outcomes with the four-component model was analysed by Bland & Altman analyses.
• Study 3: This was a cross-sectional validation study, secondary to a randomized clustered clinical trial (OBEMAT2.0). The baseline body composition data of 315 participants enrolled in the OBEMAT2.0 clinical trial was used. Body composition measurements where obtained from the four-component model likewise in study 2. BIA was also performed with a TANITA 418-BC device. A bootstrap linear regression analysis was undertaken in 249 participants (train sample) to develop a new FFM predictive equation derived from impedance raw data. This equation was then tested in the test sample (n =66) and FM and FFM was obtained. The agreement between the new equation and TANITA outputs with the four-component model was analysed with a Bland & Altman analysis.
Results: The results obtained from study 1 showed that FFM properties (hydration and density) are different between obese and non-obese people and the assumption of constant values for these properties lead to obtain biases in body composition assessment in obese children.
The study 2 results demonstrate that using calculated density of the FFM values unlike assumed constant values of the density in two-component based techniques as ADP, improves the accuracy of the body composition assessment in obese children by this technique.
The study 3 showed that the new equation derived from body impedance improves the accuracy and the precision of the BIA body composition assessment in obese children.
Conclusions: The FFM properties (hydration and density) are different when compared between obese and non-obese people. These differences might lead to assume biases when assessing body composition by current techniques based on two-component model, which usually assume constant values of this properties. The use of density of the FFM calculated measurements instead constant values improves the accuracy and precision of the body composition assessment in obese children by ADP, which is a two-component based technique.
However, ADP stills being an unaffordable technique for body composition assessment in clinical practice. The new predictive equation to assess body composition derived from body impedance improves the accuracy and the precision of BIA’s body composition assessment and it is suitable to clinical and research use.
Finally, further studies are needed to assess the accuracy and the precision of this findings in longitudinal studies and clinics follow-up to evaluate body composition changes.
