The Stayhealthy bioelectrical impedance analyzer predicts body fat in children and adults
Introduction
With the increased prevalence of overweight and obese people in the United States [1], there is a need to accurately determine body composition to assess the risk of morbidity in children and adults and also a need to offer a reliable way that individuals can track their own body composition. Currently, there are many methods available for obtaining body composition measures such as summation of skinfolds [2], bioelectrical impedance analysis (BIA) [3], bioelectrical impedance spectroscopy [4], air displacement plethysmography [5], hydrostatic weighing (HW) [6], magnetic resonance imaging [7], and dual energy x-ray absorptiometry (DXA) [8]. Because these measures of body composition provide an estimate of body fat percentage, cadaveric analysis has been used to validate reference methods such as HW and DXA by which other methods may be compared. However, HW and DXA are not always practical and can be relatively time consuming, expensive, and limited to clinical settings.
Bioelectrical impedance devices are convenient for estimating body composition and a popular choice for investigators because they can be used in both clinical and field settings. In addition, they are becoming popular for use by individuals who want to track progress when on diet and exercise regimens. Bioelectrical impedance analysis measures the body's resistance to flow of electric current between points of contact on the body and correlates well with measures of total body water [9]. Assuming that the hydration fraction for fat-free mass (FFM) is a constant, it is possible to calculate FFM from total body water and subsequently fat mass (FM) from total body weight. By incorporating variables to the measured impedance value such as body weight, height, sex, and age, prediction equations have been developed using regression analysis to better estimate body composition when compared to reference methods.
The accuracy and reliability of bioelectrical impedance devices have been validated against reference methods such as HW [10], DXA [8], and isotope dilution methods [11]. Although many studies have examined the validity of BIA for specific populations, such as children [2], [4], adults [12], athletes [6], [13], and clinical patients [11], [14], few studies have examined the validity of BIA in a large diverse population.
Traditionally, body composition methods assess the body in 2 compartments: FFM and FM. Hydrostatic weighing was developed using cadaveric analysis of FM and FFM components [15] and is considered to be a reference criterion or “gold standard” [16] by which other methods for estimating body composition are compared. Hydrostatic weighing is a 2-compartment model that measures underwater body mass from which body density is calculated and subsequently entered into an equation to determine percent body fat (%BF). Previous studies have used HW to validate bioelectrical impedance devices in children and demonstrated strong correlations (r >0.90) [6], [10].
Dual-energy x-ray absorptiometry is traditionally used for measuring changes in bone density and is increasingly being used for assessing body composition. Unlike 2-component models (FM and FFM), DXA uses a 3-component model of fat, mineral, and lean tissue mass [17] but has the limitation of high cost and radiation exposure, making it inappropriate for multiple measures and not practical for individual use at home or in physician offices.
Because DXA and HW methods are limited to a clinical setting and can be relatively time consuming and expensive, BIA may be a more practical method for measuring body composition. We hypothesized that there would be good agreement between the Stayhealthy BC1 BIA and the selected reference methods when determining body composition. Therefore, the purpose of the present study was to determine the validity and reliability of the Stayhealthy body composition analyzer BC1 using the new proprietary equation compared to HW measurements in children and DXA measurements in adults for a large diverse population.
Section snippets
Participants
Two hundred forty-five adults, 18 to 80 years old (117 men and 128 women), and 115 children, 10 to 17 years old (51 boys and 64 girls), volunteered to participate in this study conducted at the University of Southern California's Clinical Exercise Research Center, Los Angeles, Calif. Men and women were analyzed separately because of inherent sex differences in body composition and further divided into the following age groups: 18 to 35, 36 to 50, 51 to 60, 61 to 70, and 71 to 80 years. Before
Results
Data from 245 adults, 18 to 80 years old (117 men and 128 women), and 115 children, 10 to 17 years old, (51 boys and 64 girls) were included in the analyses. A total of 4 men and 7 women were excluded from the analyses for not having completed all tests. Six children were excluded from analyses because they were unable to successfully perform the HW test. The girls' and boys' data were combined for analyses. Table 1, Table 2 summarize anthropometric and mean values for %BF as measured by the
Discussion
Bioelectrical impedance analyzers are simple and cost-effective, and the technique is a noninvasive method to determine %BF. Investigators have reported reliable and valid BIA devices [6], [14], [22], [23]; however, many of these have been shown not to be interchangeable with reference methods [8], [11], [24], [25]. The purpose of the present study was to examine the hypothesis that the Stayhealthy BCA, a single-frequency, 50-kHz bioelectrical impedance device is a valid measure of %BF when
Acknowledgment
The authors would like to acknowledge Scott A. McCauley and Trina Rowe for data input; Nicolas Schweighofer for statistical support; and Colin K. Hill for his contribution to study design and editorial assistance. This study was supported in part by Stayhealthy, Inc, and the Clinical Exercise Research Center, University of Southern California.
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