Validity of total and segmental impedance measurements for prediction of body composition across ethnic population groups

Abstract

Objectives: To test the impact of body build factors on the validity of impedance-based body composition predictions across (ethnic) population groups and to study the suitability of segmental impedance measurements. Design: Cross-sectional observational study. Settings: Ministry of Health and School of Physical Education, Nanyang Technological University, Singapore. Subjects: A total of 291 female and male Chinese, Malays and Indian Singaporeans, aged 18 -69, body mass index (BMI) 16.0 -40.2 kg= m 2 . Methods: Anthropometric parameters were measured in addition to impedance (100 kHz) of the total body, arms and legs. Impedance indexes were calculated as height 2 =impedance. Arm length (span) and leg length (sitting height), wrist and knee width were measured from which body build indices were calculated. Total body water (TBW) was measured using deuterium oxide dilution. Extra cellular water (ECW) was measured using bromide dilution. Body fat percentage was determined using a chemical four-compartment model. Results: The bias of TBW predicted from total body impedance index (bias: measured minus predicted TBW) was different among the three ethnic groups, TBW being significantly underestimated in Indians compared to Chinese and Malays. This bias was found to be dependent on body water distribution (ECW=TBW) and parameters of body build, mainly relative (to height) arm length. After correcting for differences in body water distribution and body build parameters the differences in bias across the ethnic groups disappeared. The impedance index using total body impedance was better correlated with TBW than the impedance index of arm or leg impedance, even after corrections for body build parameters. Conclusions: The study shows that ethnic-specific bias of impedance-based prediction formulas for body composition is due mainly to differences in body build among the ethnic groups. This means that the use of 'general' prediction equations across different (ethnic) population groups without prior testing of their validity should be avoided. Total body impedance has higher predictive value than segmental impedance.

Validation of bioelectrical impedance analysis for total body water assessment against the deuterium dilution technique in Asian children

“…Those who have higher relative extracelluar water will have a lower resistance when measured by single frequency BIA, thus the RI will be higher for a given TBW/FFM and body weight. An ethnic difference in extracelluar water/TBW among Asian adults has been found in a previous study (Deurenberg et al, 2002b). Hence, population-specific BIA prediction equations were commonly recommended when applying BIA to predict body composition due to these ethnic differences in body composition and body build (Lohman et al, 2000;Kyle et al, 2004;Nielsen et al, 2007).…”

“…Firstly, differences in relative limb length might have an effect on the estimation of TBW and FFM by BIA. Total body impedance is largely determined by limb impedance therefore the longer the limbs, the higher the total impedance (Bracco et al, 1996;Deurenberg et al, 2002b). Those who have a higher relative leg/arm length will have a higher resistance/impedance, and thus have a lower RI at a given FFM and an underestimation of TBW and FFM (Snijder et al, 1999).…”

“…Those who have a higher relative leg/arm length will have a higher resistance/impedance, and thus have a lower RI at a given FFM and an underestimation of TBW and FFM (Snijder et al, 1999). Data on differences in relative leg length among Asian children from different origins are limited, but these differences have been found among Asian adults (Gurrici et al, 1999;Deurenberg et al, 2002b) and between Asians, blacks and Caucasians (Gallagher et al, 1996;Norgan, 1994;Deurenberg et al, 1999). Furthermore, the ethnic difference in TBW distribution can also influence the estimation of TBW and FFM by single frequency BIA.…”

Evaluation of air-displacement plethysmography and bioelectrical impedance analysis vs dual-energy X-ray absorptiometry for the assessment of fat-free mass in elderly subjects

“…BIA Whole-body impedance (Z) was measured on the left side of the body with a four-polar impedance meter (Human IM Scan, DS-Medica, Milano, Italy) at frequencies of 5, 50 and 100 kHz following international guidelines (Deurenberg, 1994). The coefficient of variation (CV) for BIA measurements in our laboratory is 2.0%, as determined by three repeated weekly measurements of three adult subjects with daily body weight variations p1.0%.…”

A simplified approach to analysing bio-electrical impedance data in epidemiological surveys

“…The relationship between bio-electrical data and TBW is known to vary significantly between populations. [1][2][3][4][5] Ideally, therefore, this relationship must first be established using validation studies where both impedance and TBW are measured in a sample representative of the population's range of body composition. Not all users adopt this approach, owing to constraints of time and cost, so TBW is often predicted using published equations derived from other populations.…”