Data from patients of three different studies performed at the Medical University Vienna were analyzed. The patients were in medical control of the outpatient clinic of pediatric obesity, dyslipidemia and nutritional medicine at the Department of Pediatrics and Adolescent Medicine, Vienna.
Study#1, the BODCOP study – a retrospective study between August 2015 and May 2016, included 67 children and adolescents. All patients were aged under 18 years and had a body mass index (BMI) exceeding the 97th percentile according to the recommendations given by Kromeyer-Hauschild and colleagues . The study was approved by the local Ethics-Committee of the Medical University Vienna (EC Nr: 1357/2016).
Study#2, Children`s KNEEs study – a randomized controlled trial between September 2015 and May 2017, data from 44 patients were collected during a 12-week strength and neuromuscular exercise program for the lower extremity on knee load, pain and function in pediatric patients with obesity . Patients were aged between 10 and 18 years and exceeded the 97th percentile described by Kromeyer-Hauschild . The study was approved by the local Ethics-Committee of the Medical University Vienna (EC Nr: 1445/2013) and was registered at clinicaltrials.gov NCT02545764.
Study#3, the MotiMove Study – a pilot for an intervention study on movement in obese adolescents between October and December 2019, included 12 patients aged between 14 and 18 years with a BMI exceeding the 90th percentile according to Kromeyer-Hauschild . The Ethical-Committee of the Medical University of Vienna approved the study (EC Nr: 1572/2019). In study#2 and #3, written informed consent was obtained from all parents and children.
Anthropometric parameters included body height and weight, and circumference at the waist, hip abdomen, and mid upper arm. These latter measures of circumferences, however, were not included in the present analysis. Procedures were as outlined previously , but a TANITA scale instead of a SECA scale. In brief, body weight was measured within 0.1 kg precision in an upright position and in underwear. These values were also applied for calculation of BIA-based body composition determination. Body height was measured in an upright facing position with feet together and the back against the wall to the nearest 0.1 cm as the maximum distance between the floor and the highest point on the head.
Measurements of body composition
The present study applied four different methods for the assessment of body composition, two of these based on bioelectrical impedance (TANITA, BIA), one on air displacement plethysmography (BOD POD), and one on dual x-ray absorptiometry (DXA). The main parameters determined and analyzed were body fat percentage (BFP, %), fat mass (FM, kg) and fat-free mass (FFM, kg). To reduce measurement variability, all measurements in each patient were conducted by the same trained team member, at the same daytime, and the same condition like an empty bladder.
TANITA and BIA
The assessment of body composition with the devices is following standard procedures . Patients were measured with the TANITA scale (Type BC-418MA, TANITA Corporation, Tokyo, Japan) and immediately afterwards with the BIA device (BIACORPUS RX 4000, Medical Healthcare GmbH, Karlsruhe, Germany).
The determination of body composition with air displacement plethysmography was conducted with the BOD POD Gold Standard Body Composition Tracking System (BOD POD COSMED Inc, USA), following instructions of the manufacturer. This type of measurement applies the principles of whole-body densitometry to determine body composition. For this, a high-precision weight assessment is combined with a body volume measurement and determination of the thoracic gas volume, and then, based on densitometric equations BFP, FM and FFM are calculated.
The DXA-based method for the determination of body composition applies the fact that fat and non-fat tissue attenuate x-rays to a different extent, allowing to calculate the proportion of each compartment following a whole-body scan.
Whole-body DXA was performed with a Hologic Horizon system A (Marlborough, MA, USA), release 2018, for estimating body composition by the same trained technicians according to the prescriptions by the manufacturer and after daily calibration. All patients were placed in supine position with the limbs in standardized way according to the guidelines. The precision and accuracy of DXA is reported as acceptable to define body composition in children . Fat mass, lean tissue mass, and bone mineral content of the whole body were measured. Radiation dose, expressed as dose area product, was 7.9 cGy·cm².
Statistical analyses were performed with the SPSS software package (SPSS Inc., Chicago, IL, version 24.0). Results are expressed as means ± SD unless otherwise indicated. Assumptions were checked before conducting parametric tests. Data on body composition methods were analyzed with paired t-tests and a p-value of < 0.05 was considered as statistically significant. Further, data obtained with TANITA and BIA were compared by the Pearson correlation coefficient, and the Bland-Altman plot was used to assess the extent of agreement between the two methods . The 95 % limits of agreement were calculated as the mean difference ± 1.96 SD .