Body Composition Measurement: A Review of

15 Pages·1998·0.12 MB·English

REVIEW ARTICLE
NutritionVol.14,No.3,1998
Body Composition Measurement: A Review
of Hydrodensitometry, Anthropometry, and
Impedance Methods
DAVID BRODIE, PHD,* VICKI MOSCRIP, MSC, HDCR,† AND ROB HUTCHEON, MSC‡
From the *Department of Movement Science and Physical Education; the †Department of Medical Imaging;
and the ‡Department of Medicine, University of Liverpool, Liverpool, United Kingdom
Date accepted: 5 July 1997
ABSTRACT
Humanbodycompositionisanexpressionofgeneticandnutritionalfactors.Itcanchangeasaconsequenceofexogenous
influences such as training, disease, or diet and is therefore of particular interest to nutrition professionals. Two of the main
methodsofestimatingbodycompositioninthisreview(hydrodensitometryandanthropometry)havebeeninusefordecades,
butthethirdmethod(bioelectricalimpedance)ismorerecent.Theprocedure,theoreticalbasis,assumptions,standarderrorof
estimates,andcomparisonswithothertechniquesarepresentedforeachofthethreemethods.Referencestogeneralandspecific
populationsarepresentedthatillustrateregressionequationsfordifferentages,ethnicgroups,andgender.Theadvantagesand
disadvantagesofthethreemethodsarereviewedwithreferencemadetothealternativecompartmentmodels.Othermethods
(DEXA,infraredinteractance)arebrieflyreviewed. Nutrition1998;14:296–310.©ElsevierScienceInc.1998
Keywords:bodycomposition,hydrodensitometry,anthropometry,electricalimpedance,DEXA,infraredinteractance
INTRODUCTION currentlyonlyavailableononemaleandonefemalesubjectand
thecostofproducingsuchmaterialis,formostscientists,prohib-
Bodycompositionisofinteresttonutritionistsbecauseofthe
itive.Theissuesofcost,availability,access,validity,portability,
impact that nutritional status, specific diet, exercise, disease, and
ethical acceptability, and intervention need to be considered in
genetics can have on the major components of the human body.
bodycompositionresearch.Thisreviewwillmakereferencetoa
Thesecomponentscanbeconsideredatatomic,molecular,cellu-
range of methods but will concentrate on three procedures that
lar,tissue-system,andwholebodylevels.Asdirectmeasurement
have merit either in an epidemiological context (anthropometry
invivoisnotpossibleinhumans,aseriesofindirectestimatesof
and electrical impedance) or as a common criterion method (hy-
body constituents have been developed. Most interest has been
drodensitometry).Aseachofthesemethodsisusedtoestimatefat
directed at the two-compartment model, which divides the body
mass and FFM components only, it is important to define these
into fat mass and fat-free mass (FFM), largely because fat pro-
terms, especially as fat and lipid are often used interchangeably.
portion is a major issue in health. However, with the advent of
Fatisthetriacylglycerolfamilyofchemicalcompounds,whereas
chemical and isotope-based methods, it has become possible to
lipid is a more general term including other compounds such as
subdividetheFFMintowater,mineral,andproteinconstituents.1Alternatively,theuseofimagingmethodshasenabledadifferent
subdivisiognlyocfebroodpyhcoomsppahrtamtiedntessinatondfats,pmhuisnclge,obliopneid,san.4dIn the chemically based
othersofttwtisosu-ec.omponent model, the fat compartment includes all lipids
(ether-extractable) with the FFM comprising all the remaining
2
constituents.
A combination of magnetic resonance imaging (MRI) and
anatomicdissectionhasproducedserialtransverseimagesevery1
HYDRODENSITOMETRY
mm through the length of the human body. Such images are
internationallyavailableontheInternet,3thereforeprovidinganat- Hydrodensitometry or underwater weighing is essentially a
omy students, teachers, and body composition scientists with a method to measure body volume. It is regarded as the most
database of unparalleled precision. Such detailed information is reliable of available techniques for the estimation of body
Correspondenceto:DavidBrodie,PhD,TheUniversityofLiverpool,DepartmentofMovementScienceandPhysicalEducation,Liverpool,L693BXUK.
Nutrition14:296–310,1998
©ElsevierScienceInc.1998 0899-9007/98/$19.00
PrintedintheUSA.Allrightsreserved. PIIS0899-9007(97)00474-7
BODYCOMPOSITIONMEASUREMENT 297
density and alternative procedures are often judged and vali- increase the error by 0.5%. Food consumption has doubled this
datedagainstthisprocedure.Acceptingtheassumptionsstated effectonbodyfatestimation.Changeswillsimilarlybecausedby
later,itisrecognizedasavalidmethodofpercentagebodyfat hyperhydration31 and dehydration.33 These effects will become
estimation. It usually involves the use of a specially con- relevantifimmediatepreviousactivitycausedfluidlossorwhen
structed tank in which the subject is seated on a suspended high fluid retention occurs during premenstruation. As a mini-
chair or frame. Because the subject is required to exhale when mum, testing should be undertaken several hours after a meal,
submerged it requires a high degree of water confidence. This with the subject defecating and urinating immediately prior to
excludes approximately one-third of middle-aged women5 and measurement.34
if the top of the tank is not near floor level it is extremely Oncebodyvolumeisestablished,wholebodydensityisesti-
difficult for excessively obese, pregnant, elderly, or disabled mated from the mass in air (M , kg) and the weight while sub-
a
subjects. Archimedes’ principle is applied by comparing the merged (W, kg), with allowances being made for residual gas
s
mass of a subject in air and under water. This involves a volume in the lungs (V) and GI gas (100 mL). Density is then
r
sensitive and continuous measurement of underwater mass for calculatedusingthefollowingequation
which a single or multiple load cell configuration linked to a
computer is ideal, as the value will fluctuate due to movement Db5Ma/{[Wa2Ws/Dw]2Vr10.1}V
and level of exhalation. Total expiration is necessary, which
whereD isthedensityofwateratthetemperatureofsubmersion.
takes several trials, and account is taken of the remaining w
The calculation of percentage body fat from body density
residual volume, water temperature, and an estimate of gut
measuresisbasedontheassumptionthatthebodyiscomposedof
volume. For those unable to access an appropriate tank, it is
twohomogenouscomponents—fatandfat-freetissue—eachhav-
possibletoconstructasuitableframewithinaswimmingpool.
ing consistent densities. The main advantage of the two-compo-
Autopsy scales have been used as an alternative to electronic
nentmodelisthatitallowsmeasurementoftheonlyconstituentof
weighing methods, but the observer has to make rapid judge-
thefat-freebodyfromwhichrelativefatandfat-freebodycontent
ments as the scale fluctuates around a mean value. The tech-
canbeestimated.Wherecertainassumptionshold,thisapproach
nique has been described fully elsewhere.6–8
offers a practical way to establish fat and fat-free body content.
Practical considerations for this method include when and
The main limitations of the two-component model approach are
how to measure residual volume, what allowance to make for
thatseparateestimatesofvariouscomponentsofthebodysuchas
thevolumeofgasinthegut,andtheeffectofpretestnutrition
muscleandbonearenotmade.Individualpredictionerrorsoffat
andexercise.Theresidualgasvolumeaccountsforabout2%of
contentcanbesubstantial,andestimatesofbodycompositionin
thesubmergedvolume,andtheaccuracyofthisvaluebecomes
populations other than young adult males may under- or over-
criticaltothecalculation,whereaverysmallchangeofdensity
estimatefatcontent.Theuseofthetwo-componentmodelhasled
produces a much larger change in the predicted percentage of
to a lack of research in the development of new methods and
body fat.9 There is an appreciable day-to-day biological vari-
limited the potential usefulness of various laboratory methods in
ation of residual volume in any given subject and this can
estimating body composition in different populations. There has
change the estimated body fat content by as much as 1%.10,11
beenamoveawayfromthetwo-componentmodeltowardthree-
Considerable controversy occurs over whether or not to mea-
orfour-componentmodelswiththeaimofimprovingthepredic-
sure the residual volume while in the tank or separately. Sub-
tion of body fat from body density. It is therefore necessary that
mergingthebodyhasbeenshownbysomeauthorstoincrease
new methods for accurate estimation of fat, fat-free body, and
residual volume12,13 and by others to decrease the residual
muscleandbonecontentarecontinuallydevelopedandevaluated.
volume.14–19 Immersion was also found by several authors to
Bodydensity,however,isnotthepreferredvaluefornutrition-
makenodifferenceinresidualvolume.20–25Theactualmethod
ists and other health professionals working with body composi-
dependslargelyonthefacilitiesavailableandincludesnitrogen
tion.Percentagebodyfatisameasuretowhichmorepeoplecan
washout8 and oxygen dilution.26 If residual volume cannot be
relateandifthedensityoffatandleanwereconsistently0.90and
measured by such direct methods Mayhew et al. (personal 1.1 g cm23, respectively,35 the conversion would be relatively
communication) recommend estimates from 24% of vital ca-
simple. The average value of studies that measured these densi-
pacity8 or from the anthropometric method of Polgar and Pro- ties36–38 was 0.9168 g cm23 for fat and 1.0997 g cm23 for lean
madht.28 Garrow et al.29 suggested that residual volume could
tissue. Even this fails to account for more individual variations
be measured by combining a body water displacement method
such as the potential for athletes to have denser bone and mus-
with an air displacement technique for the head using a ple-
cle,39,40 osteoporosis in the elderly,41 and different bone mineral
thysmograph. This method eliminates the need for total sub-
contentinpreadolescents.42
mersion of the subject. Although the equipment is more com-
Avarietyofequationsareavailabletoestimatefatfrombody
plex than that required for hydrodensitometry, it does not
density.38,43–45 The most commonly used of these are those of
require the additional equipment for measuring residual vol-
Brozeketal.44
ume. The procedure requires minimal subject cooperation due
S D
tothefactthatthepatientstandsinwatertotheneckleveland 4.57
the volume of air in the lungs and gastrointestinal (GI) tract is % bodyfat5 24.142 3100
D
measured by observing the pressure changes produced by a
pumpofknownstrokevolume.Standarddeviationsof60.3kg andSiri46
were reported when replicate measures were made by this S D
method. 4.95
The volume of gas in the intestine is usually included in the % bodyfat5 D 24.5 3100
calculation as being 100 mL30 but should be increased for large
adultsanddecreasedforchildren.Measurementsaremostrepro- The equation developed by Brozek et al.44 for the conversion of
ducibleiftakeninthefastingstate.Thepriorconsumptionoffood bodydensitytobodyfatwasbasedonthechemicalcomposition
can change the estimated body fat content by up to 1%,31 and of reference man. The equation was developed from cadaver
recent ingestion of carbonated drinks will also change the intes- chemical analysis and was proposed to be used in a young,
tinalestimate.32Whenconvertedintobodyfatestimationthiscan nonathletic,adultmalepopulation.Althoughtheoriginalequation
298 BODYCOMPOSITIONMEASUREMENT
has not been cross validated, it has been used in many research predominantly in pediatric research. Air displacement has also
studies.Sinceitsdevelopment,thisequationhassubsequentlyand been used in infants,57 babies,58 and adults.59–61 The procedure
frequentlybeenappliedtovariouspopulationsincludingchildren, describedbyGnaedingeretal.59wasabandonedbecauseofhigh
theelderly,women,athletes,andvariousracialgroups.Bonesare sources of error from lack of control over temperature, pressure,
less dense in children, women, and older subjects of both sexes, and relative humidity in the enclosed chamber. Gundlach and
whichleadstoanoverestimationofbodyfat.Lohman47discussed Visscher61controlledisothermalconditionsbutindoingsomade
the need to limit the use of the Brozek equation and replace the the procedure impractical for most subjects. More recently,62 a
conceptofreferencemanwithpopulationspecificreferencebod- method has been described that has overcome most of these
iesleadingtoadditionaldevelopmentofpopulationspecificequa- problems.TheBODPODBodyCompositionSystem,whichuses
tions. This would enable more accurate estimates of fat content therelationshipbetweenpressureandvolumetoderivethebody
frombodydensityinthesepopulations. volumeofasubjectseatedinafiberglasschamber,isdescribedin
Body density is converted to a corresponding percentage of detail for inanimate objects.62 It produced an average coefficient
body fat based on the assumption that the body is composed of ofvariation(CV)of0.026%over2d,withaSEE62of0.004Lfor
two homogenous compartments—fat and fat-free tissue—each volumes in the range 25–100 L. This new air displacement ple-
withaconstantdensity.However,inreality,bodyfatcomprisesa thysmograph was compared with hydrostatic weighing in 68
complexmixtureofglycerides,sterols,phospholipids,andglyco- adults63andwasshowntobehighlyreliableandvalidasamethod
lipids.Someoftheseconstituentsaremorelabilethanothersand, of estimating percentage body fat. The mean difference in per-
therefore, the average density of fat varies between individuals centagefat(BODPOD2hydrostaticweighing)was20.360.2
andalsowithinagivenindividualatdifferenttimes.Thesecom- (SEM). An advantage of this method of determining body com-
plicationsareusuallyignoredindensitometriccalculations.9 positionisthatitisquickandrelativelysimpletooperate,andable
As long as the assumptions implicit in these calculations are to measure populations to which hydrostatic weighing is not
recognizedthennutritionistscouldpresentbodycompositionval- appropriatesuchastheobese,elderly,anddisabled.
uesintheformofpercentagefat.However,ifrelativevaluesare Hydrodensitometry has been the experimental basis for the
neededitseemslogicaltoretainthebodycompositiondatafrom two-componentmodelofbodycompositionassessment.Accurate
hydrostaticweighingasdensities. estimates of percentage body fat can be expected provided the
The validity of the underwater weighing technique has been assumptions of proportions and densities are satisfied.64 In sub-
extensively reviewed, including the biological and technical jectswhosefat-freebodydensitydiffersfromtheassumedvalue
sources of error.48–51 The several sources of biological variation of 1.10 g/mL, then the two-component model will be less satis-
canbecompoundedbytechnicalerrorsinthebodydensitymea- factory. The use of isotope dilution to measure the water com-
surements. An estimate of the expected degree of association partment, dual-energy x-ray absorptiometry to measure mineral
between fat content and density can be made by combining the content and neutron activation analysis for protein has permitted
technical and biological sources of variation. Biological error the quantification of the subdivisions of the fat-free component.
associatedwithestimatingthepercentagefatfrombodydensityis This has permitted the density of subgroups such as different
associated with the variability in the density and composition of races,levelsofbodyfatness,gender,andphysicalactivitylevels
the fat-free body. This error must then be added to the error tobeestimatedmoreaccurately,largelyasaresultofthevarying
associatedwithmeasuringorpredictingbodydensitytogivethe proportions of mineral and water. Multicomponent models not
total error in estimation of the true percentage fat. The error only refer to chemical constituents, but can also be used to
associatedwithmeasuringorestimatingbodydensityisonlypart describe anatomical models, molecular models, and fluid meta-
of the problem and the accuracy in determining body fat is bolic models. A more detailed discussion of multicomponent
ultimately limited by biological variation in the fat-free body. models is found in Heyward and Stolarczyk65 and Heymsfield
Lohman42 suggested that hydrostatic weighing techniques, when etal.66
used to assess the percentage of body fat, may have a standard
error of estimate (SEE) as high as 2.7%, primarily because of ANTHROPOMETRY
variationsinthefat-freedensitywithinspecificpopulations. Anthropometrictechniquesfortheestimationofbodycompo-
Themainsourcesoftechnicalerrorsthathavebeenidentified sition utilize measurements of skinfold thicknesses at various
inmeasurementofbodydensityincludevariationinresiduallung sites,bonedimensions,andlimbcircumferences.Theseareused
volume,whichappearstocontributethegreatestsourceoferror, inequationstopredictpercentbodydensity,convertedtobodyfat
andsmalleramountsoferrorfromcombinedfactorsofvariation usingtheequationsshownabove.Theuseofskinfoldstopredict
in body mass, underwater weighing, and measurement of the bodyfathasbecomeoneofthemostcommonlaboratoryandfield
watertemperature.48 anthropometric techniques in body composition and nutritional
Thehydrostaticmethodremainsasomewhatfalliblecriterion status assessment.67 There have been numerous regression equa-
method.Signsofthisfallibilityhavebeenattributedtothefactthat tions developed that use some combination of anthropometric
simpleindicesofobesitysuchastotalbodymassandcircumfer- measuresaspredictorsofbodydensity.68Mosthaveusedskinfold
encemeasurementshaveshownclosercorrelationswithskinfold measures or some combination of skinfold and circumferences.
measurements than percentage body fat estimated by the hydro- Fewhaveusedcircumferencesonly.
static technique.52 The technical and biological assumptions in- The main purpose of skinfold measurements is to estimate
herentinthismethodclearlyindicatethattheyaremostlikelyto general fatness and the distribution of subcutaneous adipose tis-
be violated at the extremes of fat percentages. Therefore, this sue. The extent that the subcutaneous adipose layer reflects total
methodismostappropriateforsegmentsofthepopulationthatdo body fat varies with age, gender, and population. This method
notexhibittheextremes,especiallytheexcessivelyobese.Roche operates on the assumption that subcutaneous adipose tissue is
et al.53 provide a review on the practicalities of estimating body representative of the total body fat. This is not an unreasonable
volumebyunderwaterweighing. assumption but there will be individual differences which will
Thetechnicalconcernsofthehydrostaticweighingprocedure, invalidate the established regression equations. As the method
not the least water confidence, have been reduced by alternative relies substantially on a limited number of skinfold sites, any
bodyvolumemeasurementsuchasacousticplethysmographyand differences in adipose tissue distribution from the original vali-
air displacement. Acoustic plethysmography54–56 has been used dated equation will impact on the prediction. Therefore, any
BODYCOMPOSITIONMEASUREMENT 299
observedvariationofadiposetissuedistribitionfromthepopula- Lohman48 extensively reviewed the relationship between skin-
tion originally used in the production of the regression equation folds,bodydensity,andfatness.Heagreedwiththeneedforsuch
shouldnecessitateanalternativeequationormethodbeingused. generalized equations but also stated the need for their cross-
Theaccessibilityofthesubcutaneousfatlayerandthenonin- validationwhenappliedtospecializedsamples.Lohman48formu-
vasive nature of skinfold measurement has led to many skinfold lated seven principles of cross-validation analysis including the
applicationsandderivationsofformulae.Theseinturnhaveledto useofcomparablemeanvaluesandsimilarstandarddeviationsfor
well over 1000 published articles that have dealt directly or predictedandmeasureddensities.ItwasalsosuggestedthatSEE
indirectly with skinfold measurements. Numerous equations for shouldbereportedratherthancorrelationcoefficientsbecauseof
the prediction of body composition have been developed, using the fact that correlation coefficients are apt to be affected by
skinfold measurements as part of the equation. There have been intersample variability of fatness whereas SEE is not. The other
well over 100 equations developed that use skinfold measure- principlesrelatetotheproblemsofnonlinearityoftherelationship
mentsandotheranthropometricdimensionsinvariouspopulations betweenskinfoldsandbodydensityandtheneedforlargesamples
rangingfromathletictosedentaryandfromchildrentotheelder- tocross-validate.
ly.69–75 Most of these formulae have led to estimates of body Differences in procedures and equipment selection may also
density,althoughsomestudieshaveattemptedadirectprediction contributetosystematicerrorsincross-validationstudies.Lohman
of body fat.71–73,76 The problems associated in choosing an ap- et al.47 showed that different caliper types may affect estimates.
propriate equation have been previously well documented. They This problem was also addressed by Sinning and Wilson,76 who
haveincludedexcessiverelianceonstepwiseregressionanalysis, agreed with Lohman for the need to standardize equipment.
failure to consider the possible curvilinear relationship between SinningandWilson76alsoevaluatedtheuseofgeneralizedequa-
total body fat and skinfold data, and failure to account for the tions for college-aged women. They showed that each equation
effectofageonbodyfatdistribution.73,74 had to be validated and evaluated on its own merits. In 1984,
Many of the skinfold prediction formulae developed are spe- Thorlandetal.80crossvalidatedgeneralcurvilinearmodelsaswell
cifictoaparticularsampleofthepopulation,andarealsodepen- as selected linear models. They also found, as did Sinning and
dentupontheage,sex,nutritionalstatus,geneticbackground,and Wilson,76 that different curvilinear equations were not equally
specialistactivities.77–79 effective in estimating body density while some linear models
ThemostwidelyusedequationsareprobablythoseofDurnin werefairlyaccurate.Thesestudieshaveallidentifiedtheneedfor
andWormersley,73whotestedvariouscombinationsofskinfolds cross-validationofsuchequationspriortotheiruseonspecialized
toproducethefollowingformulaeforbodydensity.Theseequa- samples.
tionsassumedalogarithmicrelationshipbetweenobesityandthe Several authors also carried out log transformation of their
sum of bicep, tricep, suprailiac, and subscapular skinfolds. The skinfold data.72,81 The main reasons for these transformations
equations met several of the earlier criticisms with regard to a were skewing the data, measurement errors being greater for
fewernumberofvariablesrelativetothenumberofsubjects;the thickerskinfoldsthanforthinskinfolds,andexperimentallyskin-
intercorrelation of the individual skinfold reading and the curvi- fold measurements not linearly related to body density. Nonlin-
linearityoftherelationshipbetweendensityandsubcutaneousfat. earitydiffersfromsampletosamplebutisquitesignificantinthe
Males20–69years obese.Itis,therefore,advisabletointroducesuchtransformations
O
when the population under study includes subjects of extreme
D 5 1.1765 2 0.0744~log10 4S! bodytypes.
The skinfold caliper has been the most frequent method of
Women20–69years
O measuringsubcutaneousadiposetissuethickness.Thepopularity
D 5 1.1567 2 0.0717~log 4S! ofthistechniquesisattributedtothemanyadvantagesassociated
10 withitsuse.Theseadvantagesincludethefactthatitisanonin-
whereSisthesumofthetricep,bicep,superailiac,andsubscap- vasiveandfairlypain-freetechniqueandthattheskinfoldcalipers
ular skinfolds. The equation assumes a logarithmic relationship are inexpensive, easy to maintain, and simple and convenient to
betweenthissumofskinfoldsandadiposity. use.Theymaybeusedinfieldtestingaswellasinthelaboratory
As with many of the previous skinfold equations the variable duetotheirportabilityandtheydonotrequireextensivetraining
predictedbythoseofDurninandWomersley73isthebodydensity for reliable use. In order to ensure validity, proper procedures
rather than the percentage body fat. It is, therefore, possible for mustbeusedwhenobtaininganthropometricmeasures.Potential
errors to occur in the calculation of predicted density and its sourcesofmeasurementerrorincludecaliperselectionandtester
subsequent interpretation as a fat percentage. This error of esti- reliability.Testerreliabilityincludesinter-andintrameasurement
mationhasbeenreportedtobe63.5%inwomenand65%inmen erroraswellasthevarianceassociatedwithselectionofskinfold
relative to the hydrostatic criterion method.9 Shephard9 also re- site.Amajorlimitationassociatedwithskinfoldmeasurementsis
portedtheimportanceofusingage-specificequationsbecauseof the failure to estimate simultaneously all possible sources of
theslopeoftherelationshipdecreasingwithage. measurement error. Different caliper types and testers have been
TheequationsofDurninandWomersley73andthoseofJack- examinedseparatelyanditisthesetwomajorsourcesoferrorthat
son and Pollock74 are said to be “generalized” because their may interact and give different degrees of error variance for
development and application are from a wide range of ages and differentconditions.82,83
fatness. Durnin and Womersley73 were the first to consider the As with most body composition assessment techniques there
development of equations that could be used with more varied arelimitationsassociatedwithskinfoldmeasurements,whichmay
populations. They published equations with a common slope but resultininappropriateestimatesofthesubcutaneousfatthickness
adjustedtheintercepttoaccountforaging.JacksonandPollock74 andconsequentlytotalbodyfat.Theselimitationshavebeenwell
published generalized equations for males and females. They documentedandincludefactorssuchastheinabilitytopalpatethe
extended the concepts of Durnin and Womersley73 and addition- fat/muscle interface and the difficulty in obtaining interpretable
allyovercamesomeofthelimitationsofpopulation-specificequa- measurements in obese subjects.84–86 Other problems include
tions.TheequationsofJacksonandPollock74addedageintothe compressionofthefattytissueduringmeasurement,theinability
prediction equation to account for the potential changes in the to control inter- and intrasubject variations and the fact that
ratio of internal to external fat and also bone density. In 1981, measurementsmayonlybeusefulatcertainsites.48,87Interopera-
300 BODYCOMPOSITIONMEASUREMENT
torvariabilityaswellastheuseofdifferenttypesofcalipershas oftenbiggerinwomen,andther2betweenthevariablesbeing
alsocontributedtoerrorsinmeasurementofthesubcutaneousfat measured. The SEE is calculated from the formula SEE (e.g.,
layer.42 percentage body fat) 5 SD =1.0 2 r .98Therefore, for males
2
Withsomanypredictionequationsavailableitisdifficultto with a mean and standard deviation for percent fat of 20.5 6
know which one to select. A full account of the merits of 7.1%, and a correlation between variables of 0.58, the SEE is
different equations is provided by Brodie88; the categories 5.78%. Although SEEs are not provided for each component
include generalized predication equations, population-specific prediction model, Heyward and Stolarczyk65 make the case
prediction equations, equations for infants and children, and strongly for their inclusion to evaluate the relative worth of a
equations for athletes. The concept of population specific an- regression equation. Jackson et al.90 caution the use of the
thropometric regression equations for the estimation of body generalized equations for women over 40 years of age. The
composition is well known and well documented. Regression validityofgeneralizedregressionequationswasquestionedby
formulae show that although they may meet suitable limits for Norgan and Ferro-Luzzi,99 as they found a statistically signif-
reliability, their applicability to different samples is poor re- icant difference between five such equations. An alternative
sulting in large errors in estimating individual values. The strategywastocombinedatafromothersources70,100–102intoa
population specificity of body composition prediction equa- single regression equation using the sum of triceps, abdomen,
tions can be traced largely to the use of homogenous samples and subscapular skinfolds alone.
that lack sufficient size. The validity of their findings rests on The development of population specific equations has shown
the assumption that for each population studied the composi- thatageandgenderareimportantsourcesofbodydensityvaria-
tionofthefat-freebodyissimilar.Itisassumedthatthedensity tion.70,103,104 The effect of age has been shown to be significant
ofthefat-freebodyisthesamefromonepopulationtoanother. when individual differences in skinfold fat are statistically con-
Womersley et al.89 proposed that some of the differences trolled.74 Substantial gender differences in body density deter-
associated with population-specific equations are due to the mined by hydrodensitometry have been reported in the litera-
differences between males and females in their fat-free body ture.105 Body density differences between men and women have
density with females having a lower fat-free density. This led largely been attributed to differences in fat patterning and distri-
totheoverestimationoffatcontentinfemaleswhenthefat-free bution,internaltoexternalfatratios,andgenderspecificessential
body was taken to be the same as males. Their application is, fat.48,104 Fat patterning refers to differences in the anatomical
therefore, limited to specific subsamples. Validity coefficients placementofadiposetissue.Thepatternofsubcutaneousadipose
between predicted and measured body density values range tissue is known to exhibit large variations between individuals.
from r 5 0.72 to 0.84 for women and 0.85 to 0.89 for men. Garn106 maintained that women carried a greater proportion of
Therefore,theseformulaearesaidtobepopulationspecificand subcutaneous fat than men, whereas Durnin and Womersley73
theiruseforpredictivepurposesmustbequestioned.Recently, cametotheoppositeconclusion.Researchonpopulationspecific
generalized equations have been developed. This generalized equationshasshownthatage,gender,anddegreeoffatnessneed
approach uses large heterogeneous samples and builds a re- to be taken into account when estimating body density from
gression model to fit the data. The regression model accounts anthropometric variables. To provide valid estimates of body
for age and the nonlinear relationship between skinfolds, fat, compositionitis,therefore,essentialthatequationsrepresentative
and body density. The major problem with population specific ofthestudysampleareused.
equationsistheirlimitedgeneralizability.Themainadvantage Population-specific prediction equations have been produced
of the generalized approach is that one equation can replace for college students,72,92,93,95,103,107,108 soldiers,109,110 male
several population-specific equations without a loss of predic- youths,111boysandgirlsseparately,81,112obesegirls,113andpre-
tionaccuracy;theyarevalidforagreaterrangeofageandbody menarcheal and postmenarcheal girls.114 Optimizing the regres-
composition than population-specific ones. Most prediction sion equations have included such methods as stepwise regres-
equations are by the very nature of their data collection popu- sion,115maximumr2improvement,116andfactoranalysis.117,118
lation-specificbutscientificeconomycanbeachievedbyusing Equations have been specially produced for infants and chil-
generalized equations.68 They have been cross-validated in dren. Oakley et al.119 showed greater fat thicknesses in newborn
males,74 females,90 and in athletes.76,91 It is essential that females compared with males and concluded that skinfold levels
equationsusingskinfolddataarecross-validatedonothersam- could be a valuable indication of nutritional status in neonates.
ples from the same and other populations to determine its Tricepsandsubscapularskinfoldshavebeenshowntobeadequate
general applicability. It is not possible to be certain that equa- predictors in older boys120 but not in girls. Older children have
tions developed on one sample will predict body density with been studied by various researchers,81,120–123 and Nelson and
the same degree of accuracy when applied to the data of a Nelson124foundthatthebestpredictoroffatwasacombinationof
differentsample.Thecross-validationprocessinvolvestesting tricepsandsubscapular.Twoskinfoldswerealsofoundtobegood
predictionequationsonsamplesotherthantheonesusedinthe estimatesofbodydensityin8-to11-yolds122butmethodological
initialderivation.Thisprocesswillprovideinformationregard- and biological variability in children still requires additional
ing the true external validity of the equations. Several studies examination.
have compared their prediction equations with other samples In athletes, regression equations have been established for
and when the populations were similar in age, gender, and distance runners,125 volleyball, hockey, synchronized swim-
fatness, correlations and SEEs were found to be similar.92–97 ming,126 wrestlers,102 baseball, track and field, football, tennis,94
Thestrongestevidenceincross-validationofgeneralizedequa- gymnasts,127 swimmers,126,128 male athletes,94,102,125 and female
tions with regard to their accuracy and validity appears to be athletes.127–129
provided by the standard error when the equation is cross- An excellent example of the process to select specific re-
validatedonthesecondsample.TheclosertheSEsaretoeach gression equations for children, adults, seniors, the obese,
other the more accurate and valid is the equation. As well as anorexics, athletes, and different racial groups is described by
reporting the SE, the SD of the predicted density value should Heyward and Stolarczyk.65 For example, not only does it
also be reported. There is a relationship between SEE and the provideageneralizedequationforwhitewomenaged18–55y,
coefficientofdetermination(r2).Itinvolvesknowingthestan- but the specific equation for an obese, Japanese, female group
darddeviationofthecriterionvariable,whichforpercentfatis can be accessed.130
BODYCOMPOSITIONMEASUREMENT 301
In addition to the choice of sites and regression equation, the In 1979 Katch et al.131 suggested that total fat mass could be
experienceofthetester,thetypeofcaliper,andthesubject’sstate estimated from skinfold thickness (SS), surface area (A), and a
ofhydrationallneedtobeconsideredwithcare.Studiesincaliper populationspecificconstant(K),whichvariedwiththesumof11
type have shown that cost is not necessarily a good predictor of girthmeasurements.Theequationdevelopedwas:
performance. The issue of technical characteristics of available
skinfold caliper is debated fully in Brodie.88 For practical pur- Fatmass(kg)5A3SS3K
poses,ideallyusethesamecaliperwithanestablishedtechnique
In 1980 Drinkwater and Ross133 proposed some changes to
aftercheckingtheexperimenter’sreliabilityandensuringcompa-
theconstantsthatMatiekgahadused.Theyhadfoundthatinan
rable test conditions. Even having taken such precautions, the
athletic population the formulae of Matiegka showed errors of
measurement of extremely obese patients should proceed with
8%inthepredictionoftotalbodymass.Themainchangetothe
caution, ensuring that the caliper remains in one position over a
constants by Drinkwater and Ross was in the constant used in
well-definedskinfold.
the estimation of skin and subcutaneous fat. They used a
Biologicalvariationsincludeaspectsofage,gender,overall
smaller coefficient of 0.036 rather than Matiekga’s original
fatness, and body size. Older people have a greater total body
0.065. The changes of the muscle and bone constants were
fatforagivenskinfoldthickness.Likewise,womenhavemore
smaller; muscle changed from 6.5 to 6.41 and bone from 1.2
fat than men as a result of a higher level of sex-specific
to 1.25. Applying these new constants to their data Drink-
essential fat. A greater proportion of fat is stored internally as
water and Ross predicted total body mass with an accuracy
total fatness increases. Katch et al.131 propose that to compen-
of 0.8%.
sateforthebiologicalvariabilitycausedbybodysizethatboth
Drinkwateretal.134reportedtheresultsofcorrelationsbetween
surface area and skinfolds are included in body composition
Matiekga’s original anthropometric estimates and the measure-
estimation.
ments taken from the cadaver evidence of the Brussels study. It
Lohman48summarizedthemainsourcesoferrorinthepredic-
was found that the Matiegka’s formulae when applied to the
tionofbodyfatfromskinfolddataasbiologicalvariationsinthe
cadaver data underestimated the mass of skin and subcutaneous
proportion of subcutaneous fat (62.5%), biological variations in
tissueby21.9%,themassofmusclebyanaverageof8.5%,and
the distribution of subcutaneous fat (61.8%) and technical mea-
the mass of visceral tissue by 11.6%. The mass of the bone
surementerrors(60.5%).Eachsourceoferrorisindependentand
componentwasoverestimatedby24.8%.Basedonthesefindings
so the total error is 63.3% fat, slightly better than the figure
a new set of coefficients were developed for use in the original
claimedfordensitometryandofsimilarordertothatobtainedby
formulae. The new co-efficients overestimated the fat content of
manyofthemoresophisticatedindirectmethods.
thefemalesby15.9%andunderestimatedthemalefatcontentby
Externalbodymeasurementssuchasdiametersandcircumfer-
12.3%. It was evident that the results being obtained were only
encescanbeusedindependentlytoestimatebodyfatorincom-
specific to the sample of cadavers which were relatively elderly
bination with skinfolds. One of the earliest workers was
subjects.Basedonthesefindings,itbecameclearthattherewasa
Matiekga132 who used cadaver data to develop a series of equa-
need for the development of sex-specific equations.135 The pre-
tions, using external body measurements, to estimate four body
diction of body composition from cadaveric skinfold sites pro-
compartmentsofmuscle,skinandsubcutaneousfat,deepfat,and
duces theoretical concerns when applied to free-living humans.
viscera and bone. The masses of skin and subcutaneous tissue,
Oneisthatthebodytemperatureofcadaversislower,whichcould
bone and muscle were estimated independently from a series of
affectcompressibilityofskin,andanotheristhenaturaldehydra-
empiricalconstantsandanthropometricmeasurements.Theother
tion that occurs even in a relatively fresh cadaver. The elastic
component was determined by subtracting the sum of skin and
natureofskinislostshortlyafterdeathandwillcontributetoskin
subcutaneous tissue, bone, and muscle from body mass. The
compressionvariability.
equations developed for estimating the four component models
Assessmentofmusclevolumehasbeenperformedbyanthro-
are:
pometricmethodssuchascircumferenceorgirthmeasurementsof
Skin1subcutaneousadiposetissuemass(g)50.065SS/6A the limb. The thigh and arm are two of the sites where these
measurements have been obtained in the estimation of changes
where S S was the sum of six skinfolds and A was the body that have resulted from disuse, orthopaedic dysfunction, and ex-
surfacearea(cm2). ercise training. Anthropometric techniques have been useful for
measuring body and limb volumes but have had a limited use in
Bonemass(g)51.2Q2H the determination of component tissue volumes. The main prob-
lemthathasbeenidentifiedincludesthefactthatanthropometric
where Q is the average diameters of the humoral and femoral
measurementsareonlyindirectindicatorsofmusclevolume,and
condyles,theankle,andwristincentimetersandHistheheightin
girth measurements cannot differentiate between components
centimeters.
withinthecircumference.136Oneadditionallimitationisthatany
Musclemass(g)56.5r2H circumferencemeasurementhaslimitedconstructvalidityasitis
determinedbyacombinationofbonedimensions,skinthickness,
where r is the mean of the radii calculated from the maximal bodyfat,andmusclevolume.
circumferences of the arm, forearm, calf and thigh, and H is the The upper mid-arm circumference has been used in several
height,allincentimeters. nutritionalstudiestoassessproteinandenergymalnutrition.137–140
Unfortunately,asinglecircumferencemeasurementconfoundsthe
Deepfatandadiposetissuemass(g)50.206M relative measures of fat, muscle, and bone. In 1973 Gurney and
Jelliffe,141 proposed a formula for calculating the upper arm
whereMisthebodymassingrams.Ineachcase,adiposetissue
musclecross-sectionalarea.
massreferstothetotalmass,notthefatwithinadiposetissue.
This four component anatomical model has been largely ne- Musclecross-sectionalarea5(C2pT)2/4p
glected with the increasing popularity of the two component
model,whichestimatesthemassesofthefatandfat-freecompo- whereCwasthemaximumarmcircumferenceoverthetriceps
nentsofthebody. and T was the tricep skinfold measurement. The problem with
302 BODYCOMPOSITIONMEASUREMENT
this formula is that there is no allowance made for the cross- Fat was calculated as total limb volume, minus “muscle plus
sectional area of the bone contained in the area. In 1982, bone.”Comparisonofthefatwitharadiographiccriterionfound
Heymsfield142 compared the formula of Gurney and Jelliffe141 correlations in the thigh to be 0.95 and 0.85 and in the calf 0.83
against computed tomography measurements. They found that and0.86inmenandwomen,respectively.
at the maximum circumference of the triceps the cross-sec- Weltman and Katch108 extended the technique of Jones and
tional area of bone was 6.5 cm2 in women (17% of the total Pearsontocalculatesegmentalvolumesofthearmandhand,thigh
cross-sectional area) and 10 cm2 in men (18% of the total and leg, the feet and the head and neck. They found segmental
cross-sectional area). volumes could be accurately predicted from circumference mea-
In1982JelliffeandJelliffe143suggestedthatmusclevolumeof surements at the arm, thigh, and leg sites. They, therefore, sug-
theupperarmcouldbeestimatedas20%oftheupperarmlength gestedthatcircumferencemeasurementsweregoodpredictorsof
multipliedbythemusclecross-sectionalareafromtheformulaof totalbodydensityandpercentagebodyfat.
GurneyandJelliffe.141 Shephard et al.148 proposed the following formulae for the
There have been several studies108,144–148 that have used an- estimationoflimbvolume,limbfat,limbmuscle,andlimbbone:
thropometricprinciplestocalculateregionalfat,leantissue,bone
mass, and limb volumes. Segmental zone techniques have been Limbvolume(mL)5(Sc2)L/62.8
shown to be a valid method of estimating segmental lower limb
where Sc2 was the sum of the square of five circumference
volumes in adult men and women.145,149 These volumes have
measurements(cm)andLwasthelengthofthelimb(cm).
subsequently been converted to either a limb muscle volume or
percentage fat content. The theoretical development of the seg-
Limbfat(mL)5(Sc/5 ~Ss/2n!L
mental zone method for estimating total body volume and per-
centage fat is based on the intrinsic relationship that exists be- where Sc was the sum of the five limb circumferences (cm), Ss
tweenbodyvolumeandbodymass.Katchetal.150andWeltman wasthesumofskinfoldsmeasuredoverthelimb(cm),nwasthe
andKatch108werethefirsttoestablishthistheoreticalmodelfor numberofskinfoldstakenoverthelimb,andLwasthelengthof
the prediction of total body volume and, therefore, percentage
thelimb(cm).
bodyandleanbodymass.Themainreasonforthedevelopmentof
this method was to try and overcome the problems that were Limbbone(mL)53.14R2L
associated with previous procedures that had been developed to
predict body density, percentage fat, and lean body mass. They whereRwastheaverageboneradiusofthelimb,andLwasthe
demonstrated that there was an intrinsic relationship between lengthofthelimb(cm).
segmental volume, segmental circumferential measurement, and In validation of proposed equations, Shephard et al.148 dem-
body mass, showing that it was possible to predict total body onstratedgoodcorrelationbetweenmaximumoxygenintakeand
volume and percentage fat using circumference measurements, musclevolumeinthelowerlimb,whilethepercentageoffatthat
and body mass. Regression equations were found not to be pop- wascalculatedinthelimbscoincidedcloselywithpercentagefat
ulationspecificandassociatedSEoflessthan66%forpredicting estimatedbytheskinfoldmethod.
percentage fat in all samples of subjects were better than any Sadyetal.151andFreedsonetal.152suggestedthattotalbody
previouslypublishedequation. volume could be approximated from anthropometric measure-
Ingeneral,thesecalculationshavebeenrestrictedtothelimbs, ments made on 10 body segments using three geometric shapes.
whichhavetakentheformoffourormoretruncatedcones,each Coefficients of correlation with hydrostatic weighing were high
containing concentric cylinders. The basic principle underlying (0.96 in females, 0.98 in males) but there were substantial sys-
this techniques is that the whole segment volume will equal the tematicandrandomsourcesoferrorrelativetothecriterion,which
sumofitspartvolumes.Bytakingtheappropriatemeasurements, suggeststhattheaccuracyoftheirmethodsistoolowtoprovide
the volume of each geometric shape can be calculated using useful body composition information (5.46 6 1.86 L in women;
geometricformulae. 1.7461.88Linmen).
JonesandPearson145usedanumberofgirthandheightmea- The many technical difficulties associated with the accurate
surements taken serially along the limb and then used a mathe- measurementofskinfoldshaveresultedinstudiesthathaveused
matical model of truncated cones to calculate the volume of the circumferencemeasurementsasanadditionalmeansofpredicting
thigh. They suggested that the mathematical calculation of seg- body fat or as a means of adding precision to skinfold predic-
mental volumes could be used in place of water displacement or tions.95,153–156Therehavebeendifferentpredictionequationsde-
conventionalx-raytechniques.Thevolumeoflimbsegmentswas veloped using circumference measurements on each sex and dif-
calculatedusingtheformulae: ferent age groups. Although these equations have been cross-
˛ validatedondifferentsampleswithgoodresults,theystillappear
1/3L @a1b1 ~ab!# tobepopulationspecificandshouldnotbeusedintheprediction
of body fat in individuals who appear extremely obese or ex-
where a and b were the areas of two parallel cross-sections
tremelythin.157
estimated from circumference measurements and L was the dis-
The circumference-based prediction equations have been
tance separating the two cross-sections. The volume of the foot
foundtobeusefulinrankingindividualswithinagroupaccording
wascalculatedusingtheformula:
to their relative fatness. Katch et al.164 presented a series of
1/2L ~h.b! equationsandconstantsforyoungandoldermenandwomenthat
could be used in the prediction of percentage body fat. They
whereLwasthelengthofthefoot,hwastheheightfromthesole reportedtheerrorinthepredictionofbodyfatassociatedwiththe
of the foot to the first cross-section at the ankle, and b was the circumference equations to be 6 2.5–4.0%. In view of these
averagebreadthofthefoot.Correlationsof0.98inmenand0.99 relatively low errors, they suggested that the equations could be
inwomenwerefoundwhenthetotallimbvolumewascompared particularly useful in circumstances where there is no access to
with a water displacement criterion value. Muscle plus bone laboratoryfacilities.
volume was calculated by taking skinfold measurements at the It has been shown that the reliability of moderately trained
thigh and calf, and correcting cone dimensions for overlying fat. observersissubstantiallygreaterforcircumferencemeasurements
BODYCOMPOSITIONMEASUREMENT 303
ratherthanskinfoldmeasurements.9Nevertheless,thegreatercon- ipsilateral foot of the subject who lies flat on a nonconducting
struct validity of skinfold data has been found to outweigh the surfacewithlegsabducted,preferablywiththethighsnottouch-
negative impact of poor measurement reliability, and skinfold ing,althoughthismaynotbepossibleinextremelyobesesubjects.
predictionshavebeenfoundtobemoreaccuratethanthosebased Itisimportantthatthereisnometalclosetothesubjectthatmay
oncircumferences.74,122 influenceimpedancereadings(suchasametalframeonahospital
There appear to be no studies that have used circumference bed, metallic jewelry) as it may exert an influence on high fre-
measurements to predict the volume of a body segment and quency measurements,167 and that these standard test conditions
compare the calculated circumferential segmental volume with aremaintained.Theappliedcurrentisusuallyintheorderof500
volumesobtainedfromawaterdisplacementtechnique. mAforsingle(50kHz)frequencymachines,or500mAto1mA
for multifrequency machines (5 kHz to 1 mHz), and tests times
BIOELECTRICAL IMPEDANCE maylastfromafewsecondsforasinglefrequencyscantoseveral
Bioelectrical impedance analysis (BIA) is based upon the minutes for a full frequency scan. The raw outputs are generally
relationshipbetweenthevolumeoftheconductor(i.e.,thehuman visible immediately on the analyzer (resistance and reactance),
body),theconductor’slength(i.e.,thesubject’sheight),thecom- and subsequently transmitted to a host computer whereby dedi-
ponentsoftheconductor(i.e.,fatorFFMs)anditsimpedance(Z). cated software processes the data. To maintain regression data
Impedance itself reflects frequency-dependent opposition to the accuracy,interchangingprocessingsoftwarefromdifferenceman-
flowofanalternatingelectriccurrent,andcomprisesofresistive ufactureranalysersshouldbeavoided.
(R)andreactivecapacitive(Xc)components,definedasthesquare It has been used in a range of specific groups including the
rootofthesumofthesquaresoftheresistanceandreactance(Z5 elderly,168childrenandadolescents,169–175theoverweight,176–178
[R21Xc2]).159BothRandXccomponentsarefoundinbiolog- middle-aged,179 malnourished,180–182 dialysis patients,183–190 in-
ical systems, although Xc is usually very small relative to Z at fants,191,192 for nutritional analysis,193,194 during growth,195 in
lowerfrequencies(,4%),160soRandZareoftenreportedinter- eatingdisorders,196forcancerpatients,197inethnicgroups,198,199
changeably. The distinction between Z and R becomes more andinpatientswithcysticfibrosis.200
importantwiththeadventofmultifrequencyanalyzers,asXcmay Bioelectrical impedance has been used to assess lean-body
nolongerremainsosmallasfrequencyincreases. massinHIV-infectedmen,201showingnostatisticallysignificant
BIAassumesthatthevolumeofaconductorcanbededucted results between the mean lean-body mass estimate by total body
from measurements of its length (L) and resistance. This stems electricalconductivityandthosemeasuredbyBIAoraprediction
from Ohm’s Law, which states that between two points of a equationonthebasisofbodymassindex.Ottetal.202reportedthat
conductor,R5V/I,whereRismeasuredinohms,Vismeasured phaseanglealphawasthebestsinglepredictivefactorforsurvival
in volts and I, (current) in amperes. In a symmetrical isotropic ina3-ystudyofpatientswithAIDS,andKotleretal.203reported
conductor, R is directly proportional to its length (L, cm), and moreaccuratepredictionsofbodycellmassusingreactancerather
inversely proportional to its cross-sectional area (A, cm2), R 5 thanthevaluesreportedfromtheBIA.Kotleretal.203foundthat
rL/A, where ris the specific resistivity measured in ohm centi- modeling equations derived after logarithmic transformation of
meters. As volume (n) equals L 3 A, algebraic rearrangement height, reactance, and impedance were more accurate predictors
showsthatn5rL2/R.Stature(S)isusedasanindexofthelength than equations using height2/resistance. Others have found that
ofthebody,andS2/RorS2/ZformsthebasisforpredictingFFM BIA measurements within these patient groups is greatly depen-
ortotalbodywater.Thisestimationassumesthattheconductoris dentuponthepredictionequationsused,withreportedvariations
aperfectcylinderwithauniformcross-sectionalarea,whereas,in intheFFMcontentofweightlossrangingfrom55%bytotalbody
reality,therearefivecylinders(excludingthehead).Eachcylinder water,57%fromskinfoldthickness,60%fromdualenergyx-ray
has a different cross-sectional area and, therefore, contributes a absorptiometry, to 65% and 78% using two different prediction
different resistance.161 Additionally, the differences in cross-sec- equations using BIA.204 The use of gender-dependant equations
tional area are not proportional to the differences in percentage also affects accuracy. Body composition within AIDS patients
body mass. The trunk, for example, may comprise 46% of body usinginvivoneutronactivationanalysishasshownhighreliabil-
mass,buthaslittleinfluence(3%)onwholebodyresistancewhen ity with 0.99 for total body chloride to 0.84 for total body phos-
measured conventionally, the main influencing factors being the phorous.205,206
armandtheleg.150Variationsinbodyproportionsmay,therefore, It is recognized that the measurement of bioelectrical imped-
enhancetheerrorassociatedwithpercentagebodyfatpredictions. anceisinfluencedbyotherfactorsthatshouldeitherbecontrolled
Differencesinstructurealsoaffecttheconductionofthecurrent. orreported.Theseincludeelectrodeconfigurationsuchasbipolar
Thehumanbodyasaconductorishighlyanisotropic,especiallyin ortetrapolar,207–209themenstrualcycle,210,211skintemperature,212
the trunk, which additionally leads to an indication that the rela- use of oral contraceptives,213 exercise-induced dehydration,33
tionshipbetweenwholebodyresistanceandtheconductorvolume priorfood,214anddifferentbodypositions.215Ifsuchfeaturesare
withitselectrolyticconcentrationisnotstrictlylinear.FFMpre- controlled the prediction errors to calculate body fat are 3–5%.
dictions at the extremes of body fatness are less accurate,162 as Most studies report that the impedance method is reliable and
predictionequationstendtooverestimatefatmassintheleanand valid,165,166,216–219 although some report caution in the use of a
underestimate fat mass in the obese. Electrical conduction in single frequency device in a clinical setting,220 and others found
biological systems is mainly ionic,159 and proportional to fluid that body mass alone estimated FFM as accurately as any of the
volume and the number of free electrolytic ions.163 It is also bioelectrical equations in lean males.221 The single frequency
inverselyrelatedtotemperature.164Thisinfersthatthebioelectric machinemaybereplacedbymultiplefrequencyanalyzersthatare
resistance is affected by changes in body geometry, volume, abletodifferentiatebetweentotalandextracellularfluidcompart-
temperature, and electrolytic concentration, and these effects mentsinthebody.222–224Thisisbasedonthecurrentflowatlow
shouldbetakenintoconsideration. frequencies(5kHz)passingprimarilythroughextracellularfluids
Theoverallconductivityofthehumanbodyiscloselyrelated andathigherfrequencies(.200kHz)penetratingallbodytissues.
toleantissueandhasbeenvalidatedwithcriterionmethodssuch This will increase the value for assessing clinical and nutritional
ashydrodensitometryandskinfoldmeasurement.165,166Thetech- statusconsiderably.Multifrequencyanalysershavebeenshownto
nique involves attaching adhesive surface electrodes to specific produce significant improvements in the prediction of body wa-
sitesonthedorsalsurfaceofthehandandanteriorsurfaceofthe ter225–229andimprovesthestandardizationofthemethodoverthe
304 BODYCOMPOSITIONMEASUREMENT
single frequency approach.215 It should be of particular value validatedwithethnicgroups,239inthemiddleaged,238womenof
when hydration states need to be monitored such as in renal varyingages,240andinchildrenandadults.239Standarderrorsof
dialysis,230orinthemanagementoflymphoedema.231Acompar- estimatewereintherange4.9–5.5%,237anditwasfoundthatthe
ison between the single frequency and multiple frequency ap- method underestimated the percentage body fat of obese wom-
proachesyieldsimilarresults.215Comparisonswithdifferentsin- en.238,240 This was considered to be related to the bigger differ-
gle frequency devices shows that some models record a lower ences between skinfold and optical density values in sites of
impedance value than others.240 It is interesting to note that cost higherfatdepths.240Itisgenerallyconsideredthatadditionalwork
does not seem to be a major factor, mean differences of only needstobeundertakenwithinfraredinteractiontodemonstrateits
0.6%,232betweenmachines. utility. More studies should be completed to cross-validate the
Bioelectrical impedance is used to estimate total body water technique for general and specific populations. Its appeal, not
(TBW)measuredbyisotopicdilutiontechniques.Inthisinstance, unlike impedance, is its lack of intrusion, its speed, and porta-
the standard error of the estimate of TBW, under carefully con- bility.
trolledconditions,is,2Lofwater.Thisislessthana4%error The final method to consider is that of dual energy x-ray
for an adult comprising of 50 L of TBW. Prediction errors for absorptiometry (DEXA). Originally developed for bone content
youngadults,basedonthecoefficientofvariation,haveforFFM analysis, especially the clinical study of osteoporosis, it is now
beenreportedat4%orless.Errorsinthemeasurementofheight beingheraldedasapotentialcriterionmethodforbodycomposi-
and weight, error in BIA measurement, error of measurement of tion.ComparedwithMRI,itiscurrentlymorewidelyavailableas
the criterion method, and errors from the prediction equation all a research tool and is likely to be less expensive to operate and
sumtoproducethispredictionerror. maintain.DEXAhastheadvantageofbeingabletopartitionthe
Althoughthestandarderrorofestimatesisatbestreportedas body into three components; namely bone mineral, fat and lean
2.5% in humans,233 its advantages such as speed of operation, tissue.Thisdivisionissomewhatbasedonassumptionsincorpo-
safety, portability and lack of intrusion make it an ideal tool for ratedintothemanufacturer’ssoftwarebuttheresultswhencom-
epidemiologicalinvestigations. pared with hydrodensitometry compare well, providing errors in
Validationstudieshavegenerallyinvolvedhealthyadults.The the equation used to calculate percent fat from density are ac-
elderly, youth, children, and neonates provide far more limited cepted.AdditionalsupportforDEXAasamethodofbodycom-
data. Ethnic minority groups are less commonly reported than position measurement comes from the sum of the three compo-
Caucasian.Individualswhodiffersubstantiallyfromthereference nentsthatiswithin1%oftheactualbodymass.Thetechnology
populationwilllimitvalidityaswilltheaccuracyofthemeasure- ofDEXAisreviewedbyNordandPayne241andvalidationstudies
ment of the criterion variable. Specific validation would be nec- havebeenundertakenagainstpotassium-40,242,243totalbodywa-
essary for any individuals who did not conform to the basic terusingdeuteriumdilution,243,244skinfolds,245–247hydrodensito-
assumptionsapplyingtoBIAmeasurement.Thesewouldinclude metry,245,246,248–251bioelectricalimpedance,245,247andevencom-
anyconditionscausingasymmetryorproducinglocalizedchanges paredwithlardasasofttissuesubstitute.252Itwasalsofoundto
intissueatrophyorperfusion.234 have satisfactory short-term reproducibility.253 The general con-
Baumgartner’s contribution53 reviews the assumptions, appli- clusions are that DEXA is a safe method for routine use in
cability,equipment,measurementprocedure,precision,andaccu- humans,254isprecisewithalowstandarderrorofestimate247and
racyoftheBIAmethodandishighlyrecommended. has initial promise as a method for estimating body composi-
Cliniciansvalueknowledgeofbodycompositioninhealthand tion.255–257 It has already been used widely in addition to post-
illness because of the additional information provided compared menopausal women,258–260 by such groups as children,261–266
withheight,massandderivedmeasuressuchasbodymassindex. young women,267,268 the newborn,269,270 men,271 athletes,256 and
TBW’spredictivevalueisonlyvalidindiseasewhenthecentral growthhormonedeficientadults.272Nonetheless,itisimportantto
and peripheral body components are affected similarly. This is appreciate within-manufacturer variability, which can be as high
likely to apply in moderate obesity, many noninflammatory dis- as15%forthemassofbonemineral.
eases,andinearlyHIVinfection.Intheseandothers,nutritional AnyuserofDEXAforfatmassmustrememberthatestimated
statusislikelytobethemainuseofthetechnique.Haemodialysis fat is lipid (the chemical component) not adipose tissue (the
is a probable area for BIA investigation as is any disturbance of anatomical component). Nonetheless, once validated against an
the intracellular/extracellular water ratio as in protein malnutri- imagingcriterionsuchasMRI,DEXAmayprovetobeauseful
tion, injury, or inflammation. This whole area is, to date, poorly addition to the body composition options. Any validation would
researchedandwillneedtobecautiouslyinvestigatedascritically needtotakeaccountofthetheoreticaldifferencesintheimaging
ill patients will have variable ratios of TBW to FFM. Measure- modalities.
ment of nutritional replenishment for malnourished patients may
beamoreproductivelineofinvestigation.
SUMMARY
OTHER METHODS Therangeofoptionsavailableforbodycompositionmeasure-
A full review of techniques of body composition79 and a ment includes chemical, electrical, physical, and anthropometric.
critique on the variability in the measures of body fat235 are A number of these are restricted to research institutes that have
outside the scope of this article and have been undertaken else- committedhighcapitalinvestmentsuchaswholebodycountersor
where. It is, however, valuable to consider just two alternative computertomographyscanners.Manynutritionistswillfindlow-
approachesbrieflyastheyaregainingcurrentpopularityforbody cost systems that can be applied rapidly and noninvasively a
composition assessment. The first is near-infrared interactance, useful adjunct to their clinical experience. Body composition
whichisbasedontheprincipleoflightabsorptionandreflection. usinghydrodensitometry,surfaceanthropometry,bioelectricalim-
An infrared light beam is placed over the biceps muscle and pedance,orinfraredinteractanceprovidesevidenceforfatandfat
reflected energy from the fiberoptic probe is monitored by an free components, which is becoming increasingly popular in the
opticaldetector.Itcomparesthelightabsorptionpropertiesoftwo literatureandinpractice.Thisarticleprovidesanoverviewofthe
wavelengths and in combination with other anthropometric data currentliteratureandgivesabasisforfutureresearch,forpurchase
predicts body composition utilizing an appropriate regression ofequipmentorformakingdecisionstoincludebodycomposition
equation. It has been shown to be reliable236–238 and has been aspartofnutritionalactivity.
BODYCOMPOSITIONMEASUREMENT 305
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