Elsevier

Clinical Nutrition

Volume 36, Issue 3, June 2017, Pages 825-830
Clinical Nutrition

Original article
Validity and reliability of a 4-compartment body composition model using dual energy x-ray absorptiometry-derived body volume

https://doi.org/10.1016/j.clnu.2016.05.006Get rights and content

Summary

Background

Body volume (BV), one component of a four-compartment (4C) body composition model, is commonly assessed using air displacement plethysmography (BodPod). However, dual-energy x-ray absorptiometry (DEXA) has been proposed as an alternative method for calculating BV.

Aims

This investigation evaluated the validity and reliability of DEXA-derived BV measurement and a DEXA-derived 4C model (DEXA-4C) for percent body fat (%BF), fat mass (FM), and lean mass (LM).

Methods

A total sample of 127 men and women (Mean ± SD; Age: 35.8 ± 9.4 years; Body Mass: 98.1 ± 20.9 kg; Height: 176.3 ± 9.2 cm) completed a traditional 4C body composition reference assessment. A DEXA-4C model was created by linearly regressing BodPod BV with DEXA FM, LM, and bone mineral content as independent factors. The DEXA-4C model was validated in a random sub-sample of 27 subjects. Reliability was evaluated in a sample of 40 subjects that underwent a second session of identical testing.

Results

When BV derived from DEXA was applied to a 4C model, there were no significant differences in %BF (p = 0.404), FM (p = 0.295), or LM (p = 0.295) when compared to the traditional 4C model. The approach was also reliable; BV was not different between trials (p = 0.170). For BV, %BF, FM, and LM relative consistency values ranged from 0.995 to 0.998. Standard error of measurement for BV was 0.62 L, ranging from 0.831 to 0.960 kg. There were no significant differences between visits for %BF (p = 0.075), FM (p = 0.275), or LM (p = 0.542).

Conclusion

The DEXA-4C model appears to be a valid and reliable method of estimating %BF, FM, and LM. The prediction of BV from DEXA simplifies the acquisition of 4C body composition by eliminating the need for an additional BV assessment.

Introduction

The science of body composition measurement is expanding as it plays an important role in disease detection and prevention. Excess fat mass has been associated with orthopedic injury, cardiovascular disease, and other indices of metabolic dysfunction [1], [2], [3]. Conversely, inadequate lean mass and bone mineral content have been associated with increased musculoskeletal injury risk in aging and clinical populations, as well as compromised performance in athletes [4], [5]. Sophisticated anthropomorphic measures such as percent body fat (%BF), regional adiposity, and fat to lean mass ratio have been demonstrated as more suitable health predictors than the commonly used body mass index (BMI) [6], [7]. A variety of methods for assessing whole body composition have been developed to better evaluate each individual's health status, but technology is improving in order to better estimate body tissues.

Common body composition assessment techniques such as skinfold analysis and bioelectrical impedance are based on two-compartment (2C) models, which divide the body into fat mass (FM) and fat free mass (FFM). Such models assume uniform composition of FFM in making anthropomorphic predictions, despite the variation that exists in total body water (TBW), protein mass, and bone mineral content (BMC) [8], [9]. To compensate for such assumptions, multi-compartment models have been developed to individually assess the varying components of FFM [10]. A four-compartment (4C) model factoring in body mass (BM), body volume (BV), TBW, and BMC is considered by many as the gold standard in body composition [11].

The 4C model measurement, and associated body compartments, is accomplished using a variety of equipment, but also requires considerable time and cost. Dual energy x-ray absorptiometry (DEXA) is used to estimate total body BMC. The gold standard for TBW measurement is the use of deuterium oxide dilution; however, estimates have been shown to be valid when using multifrequency bioelectrical impedance spectroscopy (BIS) [12]. Historically, underwater weighing (UWW) has been the standard method of determining BV based on hydrodensitometry. In recent decades, air displacement plethsmyography (ADP) has replaced UWW as a less invasive and more reliable method of assessing BV [13], [14]. Though considered more convenient than earlier methods, ADP requires specialized equipment (BodPod®), tight fitting clothing, and may be highly variable based on subject attire and body hair [15]. Additionally, both ADP and UWW must make assumptions regarding trapped air in the digestive tract or lungs that may compromise validity in certain individuals [16].

Dual x-ray absorptiometry may serve as an alternative method of estimating BV [11], [16]. Unlike other displacement techniques, the x-ray attenuations utilized by DEXA exclude internal air voids when analyzing soft tissues, and therefore may provide more accurate volume estimations. One previous investigation from Wilson et al. [11] has suggested that DEXA may be used to determine BV, but the population utilized was small (n = 11) and the authors suggested that further validation with a larger sample is necessary. The ability to use a DEXA-derived method for BV estimation may eliminate the need for ADP and/or UWW, reducing the time and cost required to obtain BV and use in a multi-compartment model. Greater testing efficiency would make use of a 4C body composition model more practical in both clinical and laboratory settings. Therefore, the aims of the current investigation were three-fold: 1) to develop a method of deriving BV from standard DEXA tissue measurements; 2) evaluate the validity of using DEXA-derived BV in a 4C body composition model; and 3) determine the reliability of DEXA-derived BV and 4C composition variables, including %BF, FM, and LM.

Section snippets

Participants

A sample of 127 men and women (Mean ± SD; Age: 35.8 ± 9.4 years; Body Mass: 98.1 ± 20.9 kg; Height: 176.3 ± 9.2 cm, BMI: 31.4 ± 5.5 kg m−2) volunteered to participate in body composition assessments for two separate approved studies (IRB#12-1026, 14-1045). Participant BMIs ranged from normal to obese (BMI:19.9–45.6 kg m−2); with 104 Caucasians, 19 African Americans, and 3 Hispanics. A sample of 100 people was used to develop the coefficients reported in Equation (2); a subsample of 27 was used

Validity

The inverse of the density coefficients of FM, LM, and BMC determined to predict BV were 0.84 (P < 0.01), 1.03 (P < 0.01), and 11.63 (P = 0.853) respectively, with a residual volume of −3.12 L.DEXA Volume (L)=FM0.84+LM1.03+BMC11.63+(3.12)

Compared to the sub-sample, BV derived from DEXA (94.55 ± 17.74 L) was not significantly different than BodPod BV (94.33 ± 17.58 L; P = 0.295, CI: [−1.05–0.01]). No significant differences were seen between any of the traditional predictions and the body

Discussion

Traditionally, the measurement of body composition using a 4C-model has required a BV measurement using either hydrostatic weighing or ADP and measurements of TBW from deuterium oxide. This multi-compartment measurement requires about 4 h to complete for one participant, allowing for deuterium oxide to equilibrate, and is considered a gold standard [26]. The results of the current study demonstrate that a single DEXA scan may be used as an accurate method for determining BV and subsequent

Conclusions

Valid and reliable body composition techniques are essential for detecting clinical conditions associated with both over- and under-fatness, overall health, injury prevention, and tracking changes from diet and exercise [2], [4], [30], [32], [33], [34]. Despite the known improvement in precision when using a multi-compartment model for body composition, many researchers, clinicians, and coaches still use single 2C techniques or DEXA (3C) as methods for determining body composition. The choice

Conflict of interest

The authors have no conflicts to declare.

Acknowledgments

Sources of Support: This study was supported by the Nutrition Obesity Research Center (P30DK56350), North Carolina Occupational Safety and Health Education and Research Center Pilot Grant (T42OH008673), and the University of North Carolina Junior Faculty Development Award. The project described was also supported by the National Center for Advancing Translational Sciences, National Institutes of Health (1KL2TR001109). The content is solely the responsibility of the authors and does not

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