Bioelectrical impedance analysis

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Bioelectrical impedance analysis (BIA) is a commonly used method for estimating body composition, and in particular body fat. Since the advent of the first commercially available devices in the mid-1980s the method has become popular owing to its ease of use, portability of the equipment and its relatively low cost compared to some of the other methods of body composition analysis. It is familiar in the consumer market as a simple instrument for estimating body fat. BIA[1] actually determines the electrical impedance, or opposition to the flow of an electric current through body tissues which can then be used to calculate an estimate of total body water (TBW). TBW can be used to estimate fat-free body mass and, by difference with body weight, body fat.

Accuracy

Many of the early research studies showed that BIA was quite variable and it was not regarded by many as providing an accurate measure of body composition. In recent years technological improvements have made BIA a more reliable and therefore more acceptable way of measuring body composition. Nevertheless it is not a "gold standard" or reference method. Like all assessment tools, the result is only as good as the test done. Although the instruments are straightforward to use, careful attention to the method of use (as described by the manufacturer) should be given.

Simple devices to estimate body fat, often using BIA, are available to consumers as body fat meters. These instruments are generally regarded as being less accurate than those used clinically or in nutritional and medical practice. They tend to under-read body fat percentage.[2]

Dehydration is a recognized factor affecting BIA measurements as it causes an increase in the body's electrical resistance, so has been measured to cause a 5 kg underestimation of fat-free mass i.e. an overestimation of body fat.[3]

Body fat measurements are lower when measurements are taken shortly after consumption of a meal, causing a variation between highest and lowest readings of body fat percentage taken throughout the day of up to 9.9%.[4]

Moderate exercise before BIA measurements lead to an overestimation of fat-free mass and an underestimation of body fat percentage due to reduced impedance.[5] For example moderate intensity exercise for 90–120 minutes before BIA measurements causes nearly a 12 kg overestimation of fat-free mass, i.e. body fat is significantly underestimated.[6] Therefore it's recommended not to perform BIA for several hours after moderate or high intensity exercise.[7]

BIA is considered reasonably accurate for measuring groups, or for tracking body composition in an individual over a period of time, but is not considered sufficiently accurate for recording of single measurements of individuals.[8]

The accuracy of consumer grade devices for measuring BIA has not been found to be sufficiently accurate for single measurement use and are better suited for use to measure changes in body composition over time for individuals.[9] Two-electrode foot-to-foot measurement is less accurate than 4-electrode (feet, hands) and eight-electrode measurement. Results for some four- and eight-electrode instruments tested found poor limits of agreement and in some cases systematic bias in estimation of visceral fat percentage, but good accuracy in the prediction of resting energy expenditure (REE) when compared with more accurate whole-body magnetic resonance imaging (MRI) and dual-energy X-ray absorptiometry (DXA).[10]

Historical background

Electrical properties of tissues have been described since 1871. These properties were further described for a wider range of frequencies on larger range of tissues, including those that were damaged or undergoing change after death. Thomasset conducted the original studies using electrical impedance measurements as an index of total body water (TBW), using two subcutaneously inserted needles. Hoffer et al. and Nyboer first introduced the four-surface electrode BIA technique. A disadvantage of surface electrodes is that a high current (800 μA) and high voltage must be utilized to decrease the instability of injected current related to cutaneous impedance (10 000 Ω/cm2). By the 1970s the foundations of BIA were established, including those that underpinned the relationships between the impedance and the body water content of the body. A variety of single frequency BIA analyzers then became commercially available, and by the 1990s, the market included several multi-frequency analyzers. The use of BIA as a bedside method has increased because the equipment is portable and safe, the procedure is simple and noninvasive, and the results are reproducible and rapidly obtained. More recently, segmental BIA has been developed to overcome inconsistencies between resistance (R) and body mass of the trunk.

Measurement configuration

The impedance of cellular tissue can be modeled as a resistor (representing the extracellular path) in parallel with a resistor and capacitor in series (representing the intracellular path). This results in a change in impedance versus the frequency used in the measurement. The impedance measurement is generally measured from the wrist to the contralateral ankle and uses either two or four electrodes. A small current on the order of 1-10 uA is passed between two electrodes, and the voltage is measured between the same (for a two electrode configuration) or between the other two electrodes.[11]

See also

References

  1. ↑ Kyle, Ursula G.; Bosaeus, Ingvar; De Lorenzo, Antonio D.; Deurenberg, Paul; Elia, Marinos; Gómez, José Manuel; Heitmann, Berit Lilienthal; Kent-Smith, Luisa et al. (2004). "Bioelectrical impedance analysis—part I: review of principles and methods". Clinical Nutrition 23 (5): 1226–43. doi:10.1016/j.clnu.2004.06.004. PMID 15380917.  Downloadable as PDF: Part 1 Part 2
  2. ↑ "Body fat scales review and compare". 10 January 2010. Retrieved 11 January 2010. 
  3. ↑ Lukaski HC, Bolonchuk WW, Hall CB, Siders WA (April 1986). "Validation of tetrapolar bioelectrical impedance method to assess human body composition" (PDF). J. Appl. Physiol. 60 (4): 1327–32. PMID 3700310. 
  4. ↑ Slinde F, Rossander-Hulthén L (October 2001). "Bioelectrical impedance: effect of 3 identical meals on diurnal impedance variation and calculation of body composition". Am. J. Clin. Nutr. 74 (4): 474–8. PMID 11566645. "percentage of body fat varied by 8.8% from the highest to the lowest measurement in women and by 9.9% from the highest to the lowest measurement in men" 
  5. ↑ Kushner RF, Gudivaka R, Schoeller DA (September 1996). "Clinical characteristics influencing bioelectrical impedance analysis measurements". Am. J. Clin. Nutr. 64 (3 Suppl): 423S–427S. PMID 8780358. 
  6. ↑ Abu Khaled M, McCutcheon MJ, Reddy S, Pearman PL, Hunter GR, Weinsier RL (May 1988). "Electrical impedance in assessing human body composition: the BIA method". Am. J. Clin. Nutr. 47 (5): 789–92. PMID 3364394. 
  7. ↑ Dehghan M, Merchant AT (2008). "Is bioelectrical impedance accurate for use in large epidemiological studies?". Nutr J 7: 26. doi:10.1186/1475-2891-7-26. PMC 2543039. PMID 18778488. 
  8. ↑ Buchholz AC, Bartok C, Schoeller DA (October 2004). "The validity of bioelectrical impedance models in clinical populations". Nutr Clin Pract 19 (5): 433–46. PMID 16215137. "In general, bioelectrical impedance technology may be acceptable for determining body composition of groups and for monitoring changes in body composition within individuals over time. Use of the technology to make single measurements in individual patients, however, is not recommended." 
  9. ↑ Peterson JT, Repovich WES, Parascand CR (2011). "Accuracy of Consumer Grade Bioelectrical Impedance Analysis Devices Compared to Air Displacement Plethysmography" (PDF). Int J Exerc Sci 4 (3): 176–184. 
  10. ↑ Bosy-Westphal, A.; Later, W.; Hitze, B.; Sato, T.; Kossel, E.; GlÜEr, C. C.; Heller, M.; mÜLler, M. J. (2008). "Accuracy of Bioelectrical Impedance Consumer Devices for Measurement of Body Composition in Comparison to Whole Body Magnetic Resonance Imaging and Dual X-Ray Absorptiometry". Obesity Facts 1 (6): 6. doi:10.1159/000176061.  One of the eight authors of this study is employed by body composition monitor manufacturer Omron, who financed the study.
  11. ↑ "Whole body impedance- what does it measure?". 1996. Retrieved 04 December 2013. 

Further reading

External links

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