Ability of new octapolar bioimpedance spectroscopy analyzers to predict 4-component–model percentage body fat in Hispanic, black, and white adults

Ability of new octapolar bioimpedance spectroscopy analyzers to predict 4-component–model percentage body fat in Hispanic, black, and white adults1–3 Ann L Gibson, Jason C Holmes, Richard L Desautels, Lyndsay B Edmonds, and Laura Nuudi ABSTRACT Background: New, vertical, 8-electrode bioimpedance spectroscopy (BIS) analyzers provide detailed body-composition and nutritional information within 2 min. This is the first report on BIS’s accuracy in predicting relative fatness [percentage body fat (%BF)] in a heterogeneous sample according to a multicomponent model criterion. Objective: We compared %BF measurements from 2 BIS devices with those from a multicomponent model in a sample of Hispanic, black, and white adults. Design: Equal numbers of apparently healthy men and women (n ҃ 75 of each) from each racial-ethnic group, diverse in body mass index and age, volunteered. Reference %BF (%BF4C) was computed by using a 4-component (4C) model with total bone mineral content obtained from dual-energy X-ray absorptiometry, body density from underwater weighing with measured residual lung volume, and total body water from traditional BIS. Estimations from InBody 720 (%BF720) and InBody 320 (%BF320) BIS analyzers were validated against %BF4C. Results: The %BF720 (r ҃ 0.85, SEE ҃ 5.19%BF) and %BF320 (r ҃ 0.84, SEE ҃ 5.17%BF) correlations were significant (P 쏝 0.05) in the men; main effects were nonsignificant. Correlations for %BF720 (r ҃ 0.88, SEE ҃ 4.85%BF) and %BF320 (r ҃ 0.89, SEE ҃ 4.82%BF) also were significant in the women (P 쏝 0.05); there was a main effect for method but not race-ethnicity. There were no sex-specific overestimations or underestimations at the extremes of the distributions. Conclusions: BIS estimates of %BF4C were well correlated in men and women. There were no significant methodologic differences in the men. The %BF4C was significantly underestimated by %BF720 and %BF320 in the women. Am J Clin Nutr 2008;87:332– 8. KEY WORDS Bioimpedance spectroscopy, BIS, multicomponent model, percentage body fat, %BF, adults, men, women compartments of total body water (TBW). Low-level frequencies (eg, 1–50 kHz) rely on the conductive properties of extracellular fluid, whereas, at high-level frequencies (eg, 250 kHz), the conductive properties of both ICW and ECW are instrumental. Fat-free mass (FFM) and fat mass (FM) can be calculated from single- and multiple-frequency bioimpedance analysis (BIA) after the application of previously determined constants representing the water contribution to FFM. Validation of TBW assessment from traditional tetrapolar BIS by using an isotopedilution criterion for adult samples was previously reported (5, 6). Vertical, 8-point, tactile BIS analyzers have recently been discussed in the scientific literature and have appeared at trade shows and on the commercial market. These new analyzers use 4 pairs of electrodes (octapolar technology) embedded into the analyzer’s handles (thumb and palm electrodes) and floor scale (ball of foot and heel electrodes), thereby combining upper-, lower-, and total-body bioimpedance to estimate FFM and percentage body fat (%BF) from the summation of ICW and ECW. For each of the frequencies of the BIS analyzers (InBody 720 and InBody 320; Biospace Co, Ltd, Seoul, Korea), an alternating current intensity (I) of 250 ␮A is applied between the right palm electrode (E1) and the electrode at the ball of the right foot (E5). The voltage drop (V) recorded between the right and left thumb electrodes (E2 and E4, respectively) is divided by I to calculate the resistance (R) of the right arm (RRA). This process is repeated with V being recorded between E4 and the left heel electrode (E8) to obtain the resistance of the torso (RT). The resistance of the right leg (RRL) is obtained with V recorded between the right heel electrode (E6) and E8. To determine the resistance of the left arm (RLA), the alternating current is applied between the electrodes at the left palm (E3) and the ball of the left foot (E7), and V is measured between E2 and E4. The resistance of the left leg (RLL) is calculated from V measured between E6 and E8. Whole-body resistance (Rsumx) is calculated by summing the segmental resistances at frequency x, according to the following equation: 1 INTRODUCTION Water is the largest, most variable constituent of fat-free mass (FFM). Human body water content has been reported to vary with age (1, 2), body fatness (2), sex (3), and muscularity (4). In body-composition assessment, the bioimpedance spectroscopy (BIS) technique uses a spectrum of electrical frequencies to predict the intracellular water (ICW) and extracellular water (ECW) 332 From Barry University, Miami Shores, FL. Supported by Biospace Co, Ltd, Seoul, Korea, and by Major Research Instrumentation grant no. 05-515 from the National Science Foundation. 3 Reprints not available. Address reprint requests and correspondence to AL Gibson, Human Performance and Leisure Sciences/Sport and Exercise Sciences, Barry University, 11300 NE 2nd Avenue, Miami Shores, FL 33161-6695. E-mail: . Received May 28, 2007. Accepted for publication September 17, 2007. 2 Am J Clin Nutr 2008;87:332– 8. Printed in USA. © 2008 American Society for Nutrition BIOIMPEDANCE SPECTROSCOPY ESTIMATES OF %BF4C Rsumx ⫽ RRA ⫹ RLA ⫹ RT ⫹ RRL ⫹ RLL (1) The index of Rsumx (RIsumx) is calculated by using the following equation: RIsumx ⫽ Ht (cm)2/Rsumx 共⍀兲 (2) The frequencies used by the InBody 320 analyzer are 5, 50, and 250 kHz. Those used by the InBody 720 analyzer are 1, 5, 50, 250, 500, and 1000 kHz. Whereas earlier octapolar BIS studies were conducted (7–10), they involved the use of small and predominantly homogenous samples. The primary thrusts of those studies were estimation validations of water compartments (7, 9) and appendicular lean tissue mass (LTM) (8, 10). No studies were found that included a racially-ethnically diverse sample or a multicomponent reference measure. Therefore, the purpose of the present study was to cross-validate the %BF estimations of the InBody 720 and InBody 320 BIS analyzers on a diverse sample of Hispanic, black, and white adults using the Selinger 4-component (4C) model (11) as the reference method. SUBJECTS AND METHODS Subjects Participants were recruited by word-of-mouth and posted flyers in our South Florida community. After an initial screening through which inclusion criteria were verified, a testing appointment was scheduled. Inclusion criteria were freedom from metabolic disorders or other disease states that could affect muscle and bone, absence of surgical hardware such as pins and rods, a body mass index (BMI; in kg/m2) that fell within an open cell in the BMI–race-ethnicity recruitment configuration, minimum age of 18 y, and absence of pregnancy. We attempted to balance the recruitment (n ҃ 5/cell; Table 1), but we were unsuccessful in recruiting adults in the lowest BMI category; therefore, we overfilled other BMI categories (...truncated)