| The ability to accurately assess body composition, and body fat in particular, has taken on greater importance with the attention of Wellness programs, the monitoring of disease, and the prevalence of obesity. New guidelines are being developed to offer increasingly aggressive therapies for severe obesity (Bariatric care) for adults and the alarming trend of childhood obesity. While treating 'wasting' diseases, such as cancer or AIDS, it is important to monitor the effective of treatments as they pertain to changes in body mass. Add to this the growing emphasis on total body wellness and a greater awareness of the benefits of physical fitness among the medical community and general public, and it's easy to see why there is an increasing demand for body composition analysis. |
| The traditional measures of body composition testing are based on the premise that total body weight is the sum of two categories: fat mass and fat-free mass (FFM). Direct measures of FFM, total body water, or body density are used along with total body weight to estimate the absolute and relative amount of body fat. In the last decade, more sophisticated methods have been developed to separate total body weight into a four-compartment model: fat mass, body cell mass, extracellular water, and skeletal mass. |
| Providing accurate results with convenient and easy-to-use diagnostic tools, Bio-electrical Impedance Analysis(BIA) is an ideal method of body composition testing. |
Easy and quick to perform
Non-invasive
Low risk
Low cost
High predictive value
Excellent consistency for repeated measurements
Sensitive enough to detect clinically important
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| Bio-electrical Impedance Analysis (BIA) measures the impedance or resistance to the flow of a safe, low-level electric current through the body fluids contained mainly in the lean and fat tissue. Impedance is low in lean tissue, where intra-cellular and extra-cellular fluid and electrolytes are primarily contained, but high in fat tissue. Impedance is thus proportional to body water volume (TBW).
In practice, a small constant current, typically 400 uA at a fixed frequency, usually 50 kHz, is passed between electrodes spanning the body and the voltage drop between electrodes provides a measure of impedance. Prediction equations, previously generated by correlating impedance measures against "gold standard" estimates of Total Body Water (TBW) such as deuterium dilution, may be used subsequently to convert a measured impedance to a corresponding estimate of TBW. Lean body mass is then calculated from this estimate using an assumed hydration fraction for lean tissue (NOTE: Bodystat is unique in using their own regression equation for this calculation and not the assumed 73.2% used by other manufacturers). Fat mass is calculated as the difference between body weight and lean body mass. |
| Proprietary prediction equations, developed by correlating impedance measures against a "gold standard" such as deuterium dilution, convert the impedance measurement into a corresponding value of Total Body Water (TBW). Lean body mass (FFM) is then calculated from this value using a hydration fraction for lean tissue. Fat mass is calculated as the difference between body weight and lean body mass. |
| The impedance of a biological tissue comprises two components, the resistance and the reactance. The conductive characteristics of body fluids provide the resistive component, whereas the cell membranes, acting as imperfect capacitors, contribute a frequency-dependent reactive component. By measuring the impedance at 5 kHz and 200 kHz and by applying predictive equations, it is possible to estimate both Extra-Cellular Water (ECW) and TBW respectively and by deduction, Intra-Cellular Water (ICW). By measuring the impedance at 5 kHz and 200 kHz, and by applying predictive equations, it is possible to measure both Extra-Cellular Water (ECW) and TBW respectively; and by deduction, Intra-Cellular Water (ICW). ECW can be related to extra-cellular mass (ECM) and ICW to Body Cell Mass (BCM). |
| Bio-electrical Impedance Analysis has been correlated most frequently against hydrostatic (underwater) weighing, bone densitometry (DEXA), or isotope dilution as the "gold standard". Most commercial devices machines are supplied with proprietary prediction equations the details of which are hidden from the user within the software of the machine. In addition, many prediction algorithms have been published in the bio-medical press. All prediction equations include height, as a surrogate measure for the inter-electrode distance, but may also include, weight, sex or age as variables. Many studies have been undertaken not only to validate particular prediction equations but also to identify other variables which may improve the quality of the predictor. The overall precision of any given prediction equation is the sum of the precisions associated with each independent variable. |
| Today there are thousands of published scientific papers worldwide validating the use of whole body BIA technology for numerous medical and health/fitness applications. |
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