View source for Bioelectrical impedance analysis

{{Short description|Method for estimating body composition}}
'''Bioelectrical impedance analysis''' ('''BIA''') is a method for estimating [[body composition]], in particular [[body fat]] and [[muscle]] mass, where a weak [[electric current]] flows through the body, and the voltage is measured in order to calculate [[Electrical impedance|impedance]] ([[Electrical resistance|resistance]] and [[Electrical reactance|reactance]]) of the body. Most body water is stored in muscle. Therefore, if a person is more muscular, there is a high chance that the person will also have more body water, which leads to lower impedance. Since the advent of the first commercially available devices in the mid-1980s the method has become popular, owing to its ease of use and portability of the equipment. It is familiar in the consumer market as a simple instrument for estimating body fat. BIA<ref>{{cite journal | vauthors = Kyle UG, Bosaeus I, De Lorenzo AD, Deurenberg P, Elia M, Gómez JM, Heitmann BL, Kent-Smith L, Melchior JC, Pirlich M, Scharfetter H, Schols AM, Pichard C | title = Bioelectrical impedance analysis—part I: review of principles and methods | journal = Clinical Nutrition | volume = 23 | issue = 5 | pages = 1226–1243 | date = October 2004 | pmid = 15380917 | doi = 10.1016/j.clnu.2004.06.004 | author14 = Composition of the ESPEN Working Group | s2cid = 21000697 }}</ref> actually determines the [[electrical impedance]], or opposition to the flow of an electric current through body tissues, which can then be used to estimate [[total body water]] (TBW), which can be used to estimate fat-free body mass and, by difference with body weight, [[adiposity|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{{When|date=April 2023}} technological improvements have made BIA much more reliable and therefore more acceptable way of measuring body composition.{{Citation needed|date=April 2023}} Nevertheless, it is the 4-compartment model (4C) ([[DXA]] and [[MRI]] are acceptable alternatives) – and not BIA – that is regarded as the reference method in body composition analysis.<ref name = jim>{{cite journal |url= https://jim.bmj.com/content/66/5/1.10 |title=Advanced body composition assessment: from body mass index to body composition profiling |date=2018 |doi=10.1136/jim-2018-000722 |pmid=29581385 |access-date=14 February 2020 |last1=Borga |first1=Magnus |last2=West |first2=Janne |last3=Bell |first3=Jimmy D. |last4=Harvey |first4=Nicholas C. |last5=Romu |first5=Thobias |last6=Heymsfield |first6=Steven B. |last7=Dahlqvist Leinhard |first7=Olof |journal=Journal of Investigative Medicine |volume=66 |issue=5 |pages=1.10–9 |pmc=5992366 |s2cid=4726327 |doi-access=free }}</ref>
Although the instruments are straightforward to use, careful attention to the method of use (as described by the manufacturer) should be given. {{cn|date=September 2019}}
Simple devices to estimate body fat, often using BIA, are available to consumers as [[body fat meter]]s. 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 by approximately 5&nbsp;kg (±7&nbsp;kg LoA{{clarify|date=May 2024}}) on average, despite showing a linear correlation with MRI-based measurements of 0.75 and 0.81 for females and males respectively.<ref name = jim/><ref>{{cite web |url=http://www.choice.com.au/Reviews-and-Tests/Food-and-Health/Diet-and-exercise/Weight-loss/Body-fat-scales-review-and-compare.aspx |title=Body fat scales review and compare |date=10 January 2010 |access-date=11 January 2010}}</ref>
[[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&nbsp;kg underestimation of fat-free mass i.e. an overestimation of body fat.<ref name = human>{{cite journal | vauthors = Lukaski HC, Bolonchuk WW, Hall CB, Siders WA | s2cid = 44184800 | title = Validation of tetrapolar bioelectrical impedance method to assess human body composition | journal = Journal of Applied Physiology | volume = 60 | issue = 4 | pages = 1327–1332 | date = April 1986 | pmid = 3700310 | doi = 10.1152/jappl.1986.60.4.1327 }}</ref>
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 4.2% of body fat.<ref>{{cite journal | vauthors = Slinde F, Rossander-Hulthén L | title = Bioelectrical impedance: effect of 3 identical meals on diurnal impedance variation and calculation of body composition | journal = The American Journal of Clinical Nutrition | volume = 74 | issue = 4 | pages = 474–478 | date = October 2001 | pmid = 11566645 | doi = 10.1093/ajcn/74.4.474 | quote = 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, The subject with the largest decrease in percentage of body fat had a decrease of 23%, from 17.9% body fat at baseline to 13.7% body fat at measurement no. 17. | doi-access = free }}</ref>
Moderate exercise before BIA measurements lead to an overestimation of fat-free mass and an underestimation of body fat percentage due to reduced [[Electrical impedance|impedance]].<ref>{{cite journal | vauthors = Kushner RF, Gudivaka R, Schoeller DA | title = Clinical characteristics influencing bioelectrical impedance analysis measurements | journal = The American Journal of Clinical Nutrition | volume = 64 | issue = 3 Suppl | pages = 423S–427S | date = September 1996 | pmid = 8780358 | doi = 10.1093/ajcn/64.3.423S | doi-access = free }}</ref> For example, moderate intensity exercise for 90–120 minutes before BIA measurements causes nearly a 12&nbsp;kg overestimation of fat-free mass, i.e. body fat is significantly underestimated.<ref>{{cite journal | vauthors = Abu Khaled M, McCutcheon MJ, Reddy S, Pearman PL, Hunter GR, Weinsier RL | title = Electrical impedance in assessing human body composition: the BIA method | journal = The American Journal of Clinical Nutrition | volume = 47 | issue = 5 | pages = 789–792 | date = May 1988 | pmid = 3364394 | doi = 10.1093/ajcn/47.5.789 }}</ref> Therefore, it is recommended not to perform BIA for several hours after moderate or high-intensity exercise.<ref name = journal>{{cite journal | vauthors = Dehghan M, Merchant AT | title = Is bioelectrical impedance accurate for use in large epidemiological studies? | journal = Nutrition Journal | volume = 7 | page = 26 | date = September 2008 | pmid = 18778488 | pmc = 2543039 | doi = 10.1186/1475-2891-7-26 | doi-access = free }}</ref>
BIA is considered reasonably accurate for measuring groups, of limited accuracy 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.<ref>{{cite journal | vauthors = Buchholz AC, Bartok C, Schoeller DA | title = The validity of bioelectrical impedance models in clinical populations | journal = Nutrition in Clinical Practice | volume = 19 | issue = 5 | pages = 433–446 | date = October 2004 | pmid = 16215137 | doi = 10.1177/0115426504019005433 | quote = 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. }}</ref><ref>{{Cite journal |last1=Fosbøl |first1=Marie Ø |last2=Zerahn |first2=Bo |date=2015 |title=Contemporary methods of body composition measurement |journal=Clinical Physiology and Functional Imaging |language=en |volume=35 |issue=2 |pages=81–97 |doi=10.1111/cpf.12152 |pmid=24735332 |s2cid=34598395 |issn=1475-097X}}</ref>
Consumer-grade devices for measuring BIA have 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.<ref>{{cite journal | title = Accuracy of Consumer Grade Bioelectrical Impedance Analysis Devices Compared to Air Displacement Plethysmography | url = http://digitalcommons.wku.edu/ijes/vol4/iss3/2 | journal = Int. J. Exerc. Sci. |volume = 4 |issue=3 |pages=176–184 |year= 2011 |vauthors=Peterson JT, Repovich WE, Parascand CR }}</ref> The two-electrode, e.g., foot-to-foot or hand-to-hand measurement, is generally found to be less accurate than 4-electrode methods (tetra-polar technique in which the current circuit is provided by a pair of distal electrodes with impedance measured, as the voltage drop between a separate pair of proximal electrodes). Multiple electrodes, typically eight, may be used located on the hands and feet, allowing measurement of the impedance of the individual body segments{{snd}} arms, legs and torso. The advantage of the multiple electrode devices is that body segments may be measured simultaneously without the need to relocate electrodes. Results for some impedance 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).<ref>{{cite journal| vauthors = Bosy-Westphal A, Later W, Hitze B, Sato T, Kossel E, Gluer CC, Heller M, Muller MJ | title = Accuracy of bioelectrical impedance consumer devices for measurement of body composition in comparison to whole body magnetic resonance imaging and dual X-ray absorptiometry | journal = Obesity Facts | volume = 1 | issue = 6 | pages = 319–324 | year = 2008 | pmid = 20054195 | pmc = 6452160 | doi = 10.1159/000176061 }} One of the eight authors of this study is employed by body composition monitor manufacturer Omron, who financed the study.</ref>
Impedance is frequency-sensitive; at low frequency the electric current flows preferentially through extracellular water (ECW) only, while at high frequency the current can cross cell membranes and hence flows through total body water (TBW). In bioimpedance spectroscopy devices (BIS) resistance at zero and high frequency can be estimated and, at least theoretically, should provide the optimal predictors of ECW and TBW and hence body fat-free mass respectively. In practice, the improvement in accuracy is marginal. The use of multiple frequencies or BIS in specific BIA devices has been shown to have high correlation with DXA when measuring body fat percentage. The correlation with DXA can be as high as 99% when measuring fat-free mass, if strict guidelines are adhered to.<ref>{{Cite journal |last1=Miller |first1=Ryan M. |last2=Chambers |first2=Tony L. |last3=Burns |first3=Stephen P. |date=October 2016 |title=Validating InBody 570 Multi-frequency Bioelectrical Impedance Analyzer versus DXA for Body Fat Percentage Analysis |url=https://www.asep.org/asep/asep/JEPonlineOCTOBER2016_Miller.pdf |journal=Journal of Exercise Physiology Online |volume=19 |pages=71–78 |issn=1097-9751}}</ref><ref>{{cite journal |last1=Ling |first1=Carolina H. Y. |last2=de Craen |first2=Anton J. M. |last3=Slagboom |first3=Pieternella E. |last4=Gunn |first4=Dave A. |last5=Stokkel |first5=Marcel P. M. |last6=Westendorp |first6=Rudi G. J. |last7=Maier |first7=Andrea B. |title=Accuracy of direct segmental multi-frequency bioimpedance analysis in the assessment of total body and segmental body composition in middle-aged adult population |journal=Clinical Nutrition |date=October 2011 |volume=30 |issue=5 |pages=610–615 |doi=10.1016/j.clnu.2011.04.001 |pmid=21555168 |doi-access=free }}</ref> It is important to recognize that correlation is ''not'' a measure of accuracy or method agreement, BIA methods typically exhibit 2 standard deviation (2SD) limits of agreement with reference methods (e.g., DXA, MRI or 4C model) of around ±10%.
== Historical background ==
The electrical properties of tissues have been described since 1872. These properties were further described for a wider range of frequencies on a larger range of tissues, including those that were damaged or undergoing change after death.
In 1962, Thomasset conducted the original studies using electrical impedance measurements as an index of total body water (TBW), using two subcutaneously inserted needles.<ref>{{cite journal |last1=Thomasset |first1=MA |title=Proprietes bioelectrique des tissuş, Mesures de l'impedance en clinique |trans-title=Bioelectric properties of tissue. Impedance measurement in clinical medicine. Significance of curves obtained |language=fr |journal=Lyon Medical |date=15 July 1962 |volume=94 |pages=107–118 |pmid=13920843 }}</ref>
In 1969, Hoffer concluded that a whole-body impedance measurement could predict total body water. The equation (the squared value of height divided by impedance measurements of the right half of the body) showed a correlation coefficient of 0.92 with total body water. This equation, Hoffer proved, is known as the impedance index used in BIA.<ref>{{cite journal |last1=Hoffer |first1=E C |last2=Meador |first2=C K |last3=Simpson |first3=D C |title=Correlation of whole-body impedance with total body water volume. |journal=Journal of Applied Physiology |date=October 1969 |volume=27 |issue=4 |pages=531–534 |doi=10.1152/jappl.1969.27.4.531 |pmid=4898406 }}</ref>
In 1983, Nyober validated the use of whole body electrical impedance to assess body composition.<ref>{{cite conference |last1=Nyboer |first1=J. |last2=Liedtke |first2=R.J. |last3=Reid |first3=K.A. |last4=Gessert |first4=W.A. |title=Nontraumatic electrical detection of total body water and density in man |conference=Proceeding of the 6th International Conference of Electrical Bioimpedance |pages=381–384 |year=1983 }}</ref>
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, such as RJL Systems and its first commercialized impedance meter.
In the 1980s, Lukaski, Segal, and other researchers discovered that the use of a single frequency (50&nbsp;kHz) in BIA assumed the human body to be a single cylinder, which created many technical limitations in BIA. The use of a single frequency was inaccurate for populations that did not have the standard body type. To improve the accuracy of BIA, researchers created empirical equations using empirical data (gender, age, ethnicity) to predict a user's body composition.
In 1986, Lukaski published empirical equations using the impedance index, body weight, and reactance.<ref name="human" />
In 1986, Kushner and Scholler published empirical equations using the impedance index, body weight, and gender.<ref>{{cite journal | vauthors = Kushner RF, Schoeller DA | title = Estimation of total body water by bioelectrical impedance analysis | journal = The American Journal of Clinical Nutrition | volume = 44 | issue = 3 | pages = 417–424 | date = September 1986 | pmid = 3529918 | doi = 10.1093/ajcn/44.3.417 }}</ref>
However, empirical equations were only useful in predicting the average population's body composition and was inaccurate for medical purposes for populations with diseases.<ref name="journal" /> In 1992, Kushner proposed the use of multiple frequencies to increase the accuracy of BIA devices to measure the human body as 5 different cylinders (right arm, left arm, torso, right leg, left leg) instead of one. The use of multiple frequencies would also distinguish intracellular and extracellular water.<ref>{{cite journal | vauthors = Kushner RF | title = Bioelectrical impedance analysis: a review of principles and applications | journal = Journal of the American College of Nutrition | volume = 11 | issue = 2 | pages = 199–209 | date = April 1992 | doi = 10.1080/07315724.1992.12098245 | pmid = 1578098 }}</ref>
By the 1990s, the market included several multi-frequency analyzers and a couple of BIS devices. 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 the body mass of the trunk.
In 1996, an eight-polar stand-on BIA device, [https://www.inbody.co.kr/ InBody], that did not utilize empirical equations was created and was found to "offer accurate estimates of TBW and ECW in women without the need of population-specific formulas."<ref>{{cite journal | vauthors = Sartorio A, Malavolti M, Agosti F, Marinone PG, Caiti O, Battistini N, Bedogni G | title = Body water distribution in severe obesity and its assessment from eight-polar bioelectrical impedance analysis | journal = European Journal of Clinical Nutrition | volume = 59 | issue = 2 | pages = 155–160 | date = February 2005 | pmid = 15340370 | doi = 10.1038/sj.ejcn.1602049 | hdl = 11380/310281 | url = https://iris.unimore.it/bitstream/11380/310281/1/EJCNsartorio2005.pdf | doi-access = free }}</ref>
In 2018, [[AURA Devices]] brought the fitness tracker AURA Band with built-in BIA.<ref>{{cite web |last1=Allison |first1=Connor |title=Aura Band's hydration tracking will tell you when to take a drink |url=https://www.wareable.com/fitness-trackers/aura-band-body-composition-hydration-3849 |website=Wareable|date=2 May 2018 }}</ref>
In 2020 BIA became available for Apple Watch users with the accessory AURA Strap with built-in sensors.<ref>{{cite web |last1=Cooper |first1=Daniel |title=The Aura Strap adds new tricks to your Apple Watch |url=https://www.engadget.com/aura-strap-hydration-wearable-140010400.html |website=Engadget|date=30 September 2020 }}</ref>
By the early 2020’s smartwatches like the [[Samsung Galaxy Watch 4]] contained built in BIA’s.
== 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{{snd}} the resistance that of intracellular fluid and the capacitor the cell membrane). This results in a change in impedance versus the frequency used in the measurement. Whole-body impedance is generally measured from the wrist to the ipsilateral ankle and uses either two (rarely) or four (overwhelmingly) electrodes. In the 2-electrode (bipolar) configuration a small current on the order of 1–10&nbsp;μA is passed between two electrodes, and the voltage is measured between the same, whereas in the tetrapolar arrangement resistance is measured between as separate pair of proximally located electrodes. The tetrapolar arrangement is preferred, since measurement is not confounded by the impedance of the skin–electrode interface<ref>{{cite journal |last1=Foster |first1=K. R. |last2=Lukaski |first2=H. C. |title=Whole-body impedance—what does it measure? |journal=The American Journal of Clinical Nutrition |date=September 1996 |volume=64 |issue=3 |pages=388S–396S |doi=10.1093/ajcn/64.3.388S |pmid=8780354 |doi-access=free }}</ref>
==Phase angle==
In bioelectrical impedance analysis in humans, an estimate of the [[Phasor|phase angle]] can be obtained and is based on changes in resistance and reactance as alternating current passes through tissues, which causes a phase shift. A phase angle therefore exists for all frequencies of measurement although conventionally in BIA it is phase angle at a measurement frequency of 50&nbsp;kHz that is considered. The measured phase angle therefore depends on several biological factors. Phase angle is greater in men than women and decreases with increasing age.<ref>{{cite journal |last1=Barbosa-Silva |first1=M. C. |title=Bioelectrical impedance analysis: population reference values for phase angle by age and sex |journal=American Journal of Clinical Nutrition |date=2005 |volume=82 |issue=1 |pages=49–52 |pmid=16002799 |url=http://ajcn.nutrition.org/content/82/1/49.long |access-date=3 April 2016 |display-authors=etal |doi=10.1093/ajcn.82.1.49 |doi-access=free}}</ref>
== See also ==
* [[Body fat percentage]]
* [[Impedance spectroscopy]]
* [[Electrical impedance tomography]]
== References ==
{{reflist}}
== Further reading ==
{{refbegin}}
* {{cite journal |first1=Cheng-Chi |last1=Tsao |first2=Kwan-Hwa |last2=Lin |first3=Jin-Shin |last3=Lai |first4=Ching |last4=Lan | name-list-style = vanc |title=Reliability of body fat measurement: Skinfold, bioelectrical impedance analysis and infrared |journal=Journal of the Physical Therapy Association of the Republic of China |date=September 1995 |volume=20 |issue=2 |pages=102–8 |doi=10.29616/JPTAROC.199509.0002 |url=http://www.airitilibrary.com/searchdetail.aspx?DocIDs=10137688-199509-20-2-102-109-a}}
* {{cite journal | vauthors = Máttar JA | title = Application of total body bioimpedance to the critically ill patient. Brazilian Group for Bioimpedance Study | journal = New Horizons | volume = 4 | issue = 4 | pages = 493–503 | date = November 1996 | pmid = 8968982 }}
* {{cite journal | vauthors = Heber D, Ingles S, Ashley JM, Maxwell MH, Lyons RF, Elashoff RM | title = Clinical detection of sarcopenic obesity by bioelectrical impedance analysis | journal = The American Journal of Clinical Nutrition | volume = 64 | issue = 3 Suppl | pages = 472S–477S | date = September 1996 | pmid = 8780366 | doi = 10.1093/ajcn/64.3.472S | doi-access = free }}
* {{cite journal | vauthors = Dehghan M, Merchant AT | title = Is bioelectrical impedance accurate for use in large epidemiological studies? | journal = Nutrition Journal | volume = 7 | pages = 26 | date = September 2008 | pmid = 18778488 | pmc = 2543039 | doi = 10.1186/1475-2891-7-26 | doi-access = free }}
{{refend}}
== External links ==
* [https://web.archive.org/web/20160430204842/http://www.isebi.org/ The International Society for Electrical Bioimpedance]
* [https://web.archive.org/web/20070701092014/http://florey.biosci.uq.edu.au/BIA/index.html Bioimpedance Analysis Electronic Media Review]
[[Category:Anthropometry]]
[[Category:Classification of obesity]]
[[Category:Electrophysiology]]
[[Category:Impedance measurements]]
[[Category:Sports nutrition]]