British Journal of Nutrition

Full Papers

Comparison of dual-energy X-ray absorptiometry, air displacement plethysmography and bioelectrical impedance analysis for the assessment of body composition in severely obese Caucasian children and adolescents

Stefano Lazzera1a2, Giorgio Bedognia3, Fiorenza Agostia1, Alessandra De Cola1, Daniela Mornatia1 and Alessandro Sartorioa1a4 c1

a1 Istituto Auxologico Italiano, IRCCS, Laboratorio Sperimentale Ricerche, Auxo-endocrinologiche, Verbania, Italia

a2 Dipartimento di Scienze e Technologie Biomediche, Università di Udine, Italia

a3 Unità di Epidemiologia Clinica, Centro Studi Fegato, Basovizza (Trieste), Italia

a4 Istituto Auxologico Italiano, IRCCS, Divisione di Auxologia, Verbania, Italia

Abstract

The objectives of the present study were to compare body composition assessed by dual-energy X-ray absorptiometry (DXA), air displacement plethysmography (ADP) and bioelectrical impedance analysis (BIA) in severely obese Caucasian children and adolescents and to develop and validate new equations for predicting body composition from BIA using DXA as the reference method. Body composition was assessed in fifty-eight obese children and adolescents (BMI 34·4 (sd 4·9) kg/m2) aged 10–17 years by DXA, ADP and BIA. ADP body fat content was estimated from body density using equations devised by Siri (ADPSiri) and Lohman (ADPLohman). In the whole sample, the Bland–Altman test showed that ADPSiri and ADPLohman underestimated percentage fat mass (%FM) by 2·1 (sd 3·4) and by 3·8 (sd 3·3) percent units (P < 0·001), respectively, compared to DXA. In addition, compared to DXA, BIA underestimated %FM by 5·8 (sd 4·6) percent units in the whole group (P < 0·001). A new prediction equation (FFM (kg) = 0·87 × (stature2/body impedance)+3·1) was developed on the pooled sample and cross-validated on an external group of sixty-one obese children and adolescents. The difference between predicted and measured FFM in the external group was − 1·6 (sd 2·9) kg (P < 0·001) and FFM was predicted accurately (error < 5 %) in 75 % of subjects. In conclusion, DXA, ADP and the BIA are not interchangeable for the assessment of %FM in severely obese children and adolescents. The new prediction equation offers an alternative approach to DXA for the estimation of body composition in severely obese children and adolescents.

(Received June 07 2007)

(Revised January 08 2008)

(Accepted January 10 2008)

(Online publication February 18 2008)

Correspondence:

c1 Corresponding author: Dr Alessandro Sartorio, fax +39 02 619112435, email sartorio@auxologico.it

Footnotes

Abbreviations: ADP, air displacement plethysmography; ADPSiri and ADPLohman, body-fat-content equations devised by Siri and Lohman respectively; BIA, bioelectrical impedance analysis; BMC, bone mineral content; BMI-SDS, standard deviation score for BMI; BW, body weight; DXA, dual-energy X-ray absorptiometry; FM, fat mass; %FM, percentage fat mass; FFM, fat-free mass; RMSE, root mean squared error of the estimate; Z, whole-body impedance; ZI, impedance index

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