body composition assessment

Illinois State University

Body Composition Assessment

Reference MethodsReference Methods


Reference Methods

• Laboratory methods provide reference or Laboratory methods provide reference or criterion measures for the derivation and criterion measures for the derivation and evaluation of body composition field evaluation of body composition field methods and prediction equations.methods and prediction equations.


Reference Methods

• Generally more expensive, Generally more expensive,

• more inconvenient, more inconvenient,

• and more time-consuming than field and more time-consuming than field methods, methods,

• but have a greater accuracy.but have a greater accuracy.


Reference Methods

• Nevertheless, all laboratory methods make Nevertheless, all laboratory methods make certain assumptions and are still subject to certain assumptions and are still subject to some measurement error.some measurement error.

• Thus, a true Thus, a true “gold standard”,“gold standard”, or perfect or perfect reference method for in vivo body reference method for in vivo body composition assessment does not exist.composition assessment does not exist.


Densitometry

• Refers to the general procedure of Refers to the general procedure of estimating body composition from body estimating body composition from body density.density.


Density

DDbb = m/V = m/V


Densitometry

• The primary requirement for accurately The primary requirement for accurately estimating body density is to obtain an estimating body density is to obtain an accurate measure of body volume.accurate measure of body volume.


Densitometry

• Body volume can be measured using either Body volume can be measured using either hydrodensitometry (underwater weighing) hydrodensitometry (underwater weighing) or air displacement plethysmography (Bod or air displacement plethysmography (Bod Pod)Pod)


Hydrodensitometry

• Also know as hydrostatic weighing, or Also know as hydrostatic weighing, or underwater weighing, provides an estimate underwater weighing, provides an estimate of total body volume from the water of total body volume from the water displaced by the body when it is fully displaced by the body when it is fully submerged.submerged.


Hydrodensitometry

• When combined with a measure of residual When combined with a measure of residual volume, this method provides a good volume, this method provides a good measure of body volume from which body measure of body volume from which body density can be easily calculated.density can be easily calculated.


Hydrodensitometry

• Long considered a Long considered a “gold standard”,“gold standard”, hydrodensiometry often has been used as hydrodensiometry often has been used as the criterion method in validation studies of the criterion method in validation studies of new body composition assessment methodsnew body composition assessment methods


Hydrodensitometry

• There are limitations to hydrodensitometry, There are limitations to hydrodensitometry, especially when applied across a wide range especially when applied across a wide range without adjustments for the changes that without adjustments for the changes that occur with growth, maturation, and aging.occur with growth, maturation, and aging.


Hydrodensitometry

• Although density can be estimated with Although density can be estimated with acceptable precision and accuracy in most acceptable precision and accuracy in most groups, groups, the assumption of an invariant fat-the assumption of an invariant fat-free compositionfree composition, commonly used to , commonly used to convert density to composition, may not be convert density to composition, may not be valid for many individuals.valid for many individuals.


Hydrodensitometry

• The magnitude of the deviation from the The magnitude of the deviation from the assumed fat-free composition, more than assumed fat-free composition, more than measurement errors in body density, measurement errors in body density, ultimately determines the accuracy of ultimately determines the accuracy of densitometric estimates of body densitometric estimates of body composition for any individual or group.composition for any individual or group.


Body Composition Models

• The density of any material is a function of The density of any material is a function of the proportions and densities of its the proportions and densities of its components.components.



• In the classic two-component model of In the classic two-component model of body composition, body weight is divided body composition, body weight is divided into fat (F) and fat free fractions (FFM).into fat (F) and fat free fractions (FFM).



• The FFM is a heterogeneous compartment The FFM is a heterogeneous compartment that can be further divided into its primary that can be further divided into its primary constituents of water (W), protein (P), and constituents of water (W), protein (P), and mineral (M) making up a 4 component mineral (M) making up a 4 component model.model.



• The two most commonly used density The two most commonly used density equations are the:equations are the:

• SiriSiri

• BrozekBrozek



• Except for the very lean and obese, for Except for the very lean and obese, for whom the Brozek equation is better suited, whom the Brozek equation is better suited, the two equations give similar results.the two equations give similar results.


Assumptions and Validity

AssumptionsAssumptions

• 1. The separate densities of the body 1. The separate densities of the body components are additive.components are additive.

• 2. The densities of the constituents of the 2. The densities of the constituents of the body are relatively constant from person to body are relatively constant from person to person.person.



• 3. The proportions of the constituents other 3. The proportions of the constituents other than fat (or adipose tissue in the case of the than fat (or adipose tissue in the case of the Brozek equation) are relatively constant Brozek equation) are relatively constant from person to person.from person to person.

• 4. The person being measured differs from 4. The person being measured differs from a standard reference body only in the a standard reference body only in the amount of body fat or adipose tissue.amount of body fat or adipose tissue.



• The assumption of an invariant nonfat The assumption of an invariant nonfat compartment is tenuous.compartment is tenuous.– Studies based on chemical and anatomical Studies based on chemical and anatomical

models have demonstrated considerable models have demonstrated considerable variation in FFM composition and density due variation in FFM composition and density due to growth and maturation, specialized training, to growth and maturation, specialized training, aging, and race.aging, and race.



• Even within a population, there is Even within a population, there is considerable inter-individual variation that considerable inter-individual variation that challenges the assumption of FFM challenges the assumption of FFM “chemical constancy”.“chemical constancy”.



• Although the multi-component (3C or 4C) Although the multi-component (3C or 4C) approach is preferred, it is commonly not approach is preferred, it is commonly not possible to measure water and mineral due possible to measure water and mineral due to a lack of equipment, time constraints, or to a lack of equipment, time constraints, or expense. expense.


Underwater Weighing

• Based on Archimede’s Based on Archimede’s principle that a body principle that a body immersed in a fluid is immersed in a fluid is acted on by a acted on by a buoyancy force, which buoyancy force, which is evidenced by a is evidenced by a “loss” of weight equal “loss” of weight equal to the weight of the to the weight of the displaced fluid.displaced fluid.


Underwater Weighing

• Thus, when a subject is submerged in water, Thus, when a subject is submerged in water, body volume is equal to the loss of weight body volume is equal to the loss of weight in water, corrected for the density of water in water, corrected for the density of water (Dw) corresponding to the temperature of (Dw) corresponding to the temperature of the water at the time of submersion:the water at the time of submersion:

V = (Wa-Ww)/DwV = (Wa-Ww)/Dw

• where Wa and Ww are the subject’s weight where Wa and Ww are the subject’s weight in air and water, respectively.in air and water, respectively.


Underwater Weighing

• Therefore, body density can be calculated Therefore, body density can be calculated by:by:

Db = ____Db = ____WaWa________________

(Wa-Ww)(Wa-Ww) - (RV +100) - (RV +100)

DwDw


Underwater Weighing

• Residual volume is commonly measured Residual volume is commonly measured using either the closed-circuit approach, using either the closed-circuit approach, where there is a dilution and eventual where there is a dilution and eventual equilibration of an inert gas or helium, or equilibration of an inert gas or helium, or the open circuit approach where nitrogen is the open circuit approach where nitrogen is “washed-out” of the lungs during a “washed-out” of the lungs during a specified period of oxygen breathing.specified period of oxygen breathing.


Underwater Weighing

• Both approaches yield precise estimates of Both approaches yield precise estimates of residual volume and with appropriate residual volume and with appropriate equipment and procedural modifications equipment and procedural modifications can be used to estimate residual volume can be used to estimate residual volume with the subject either inside the tank with the subject either inside the tank (simultaneously with underwater weighing) (simultaneously with underwater weighing) or outside the tank.or outside the tank.


Subject Preparation

• Ideally UWW should be measured with the Ideally UWW should be measured with the subject having fasted at least four hours and subject having fasted at least four hours and having refrained from strenuous exercise having refrained from strenuous exercise and other situations than can cause unusual and other situations than can cause unusual dehydration or over hydration.dehydration or over hydration.


Subject Preparation

• The subject should avoid gas producing The subject should avoid gas producing foods for at least 12 hours and there should foods for at least 12 hours and there should be no smoking for at least 3 hours prior to be no smoking for at least 3 hours prior to weighing.weighing.


Subject Preparation

• Prior to weighing, subjects are instructed to Prior to weighing, subjects are instructed to void the bladder and defecate.void the bladder and defecate.

• Subjects should be nude or wearing Subjects should be nude or wearing lightweight, tight-fitting nylon swimsuits or lightweight, tight-fitting nylon swimsuits or their equivalent to minimize trapped air.their equivalent to minimize trapped air.


Subject Preparation

• Bathing caps should not be worn since they Bathing caps should not be worn since they trap air bubbles.trap air bubbles.

• If possible, subjects should shower prior to If possible, subjects should shower prior to entering the tank to remove organic wastes entering the tank to remove organic wastes such as perspiration and body oils that tend such as perspiration and body oils that tend to cloud the water.to cloud the water.


Underwater Weighing

• There are several methodological issues to There are several methodological issues to consider when estimating body volume consider when estimating body volume from underwater weight.from underwater weight.


Underwater Weighing

• These include These include – subject position, subject position, – residual volume,residual volume,– number of trials and selection criterianumber of trials and selection criteria– alternative lung volumes, alternative lung volumes, – and head placement.and head placement.


Underwater Weighing

• The measurement of RV at the time of The measurement of RV at the time of underwater weighing is underwater weighing is – time-efficient, time-efficient, – easier on subjects for whom multiple trials are easier on subjects for whom multiple trials are

burdensome, burdensome, – and contributes to more valid estimates of body and contributes to more valid estimates of body

density.density.


Underwater Weighing

• RV can be estimated by multiplying VC by:RV can be estimated by multiplying VC by:

• 24% in males24% in males

• 28% in females28% in females


Underwater Weighing

To increase the accuracy of the results use:To increase the accuracy of the results use:

• 1. The highest weight obtained if it appears 1. The highest weight obtained if it appears more than twice.more than twice.

• 2. The second highest weight if it is observed 2. The second highest weight if it is observed more than once and the first criterion is not more than once and the first criterion is not satisfied.satisfied.

• 3. The third highest weight if neither 1 or 2 3. The third highest weight if neither 1 or 2 are met.are met.


Underwater Weighing

• Doing four or five trials and using the Doing four or five trials and using the average of three trials that agree within 100 average of three trials that agree within 100 g is an acceptable alternative in subjects for g is an acceptable alternative in subjects for whom 10 trials is burdensome.whom 10 trials is burdensome.


Underwater Weighing

• Expect an error of Expect an error of ++ 2%. 2%.– All variables must be measured as accurately as All variables must be measured as accurately as

possible to minimize the combined total error.possible to minimize the combined total error.


Other Methods

• There are several other methods for There are several other methods for estimating body volume, including estimating body volume, including – water displacement with a whole-body water displacement with a whole-body

volumeter, volumeter, – gas dilution, gas dilution, – whole-body plethysmography, whole-body plethysmography, – and the buoyancy method.and the buoyancy method.


Other Methods

• With the exception of the Bod Pod ( a form With the exception of the Bod Pod ( a form of whole-body plethysmography), these of whole-body plethysmography), these methods are not used commonly for body methods are not used commonly for body composition assessment, due either to composition assessment, due either to expense or to the difficulty of obtaining expense or to the difficulty of obtaining precise and accurate estimates of volume.precise and accurate estimates of volume.


Water Displacement

• Similar to underwater weighing except that Similar to underwater weighing except that the actual volume of water displaced by the the actual volume of water displaced by the subject is measured rather than the loss of subject is measured rather than the loss of weight in water. weight in water.


Gas Dilution

• Body volume can be estimated from gas Body volume can be estimated from gas dilution using an inert gas such as helium as dilution using an inert gas such as helium as a tracer.a tracer.


Gas Dilution

• To do so, a known volume of helium is To do so, a known volume of helium is allowed to mix freely with the air in a small allowed to mix freely with the air in a small closed chamber of constant volume in closed chamber of constant volume in which the subject is enclosed.which the subject is enclosed.


Gas Dilution

• This technique has the advantage of not This technique has the advantage of not requiring a measurement of residual lung requiring a measurement of residual lung volume since the lungs comprise a part of volume since the lungs comprise a part of the difference between the chamber and the difference between the chamber and subject volumes.subject volumes.


Gas Dilution

• Also helium dilution is applicable to Also helium dilution is applicable to individuals from infancy through old age, individuals from infancy through old age, whether healthy or ambulatory, and it whether healthy or ambulatory, and it requires relatively little subject cooperation requires relatively little subject cooperation and effort.and effort.


Gas Dilution

• However, the technique isHowever, the technique is– more complex than others, more complex than others, – has a relatively high initial cost, has a relatively high initial cost, – and requires continuous calibration checks and and requires continuous calibration checks and

very precise measurements of helium very precise measurements of helium concentrations to discriminate between subjects concentrations to discriminate between subjects of varying volumes.of varying volumes.


Plethysmography

• Body volume can be estimated using a Body volume can be estimated using a plethysmograph, which eliminates the need plethysmograph, which eliminates the need for total immersion of the subject.for total immersion of the subject.


Plethysmography

• This method used a closed vessel (e.g., Bod This method used a closed vessel (e.g., Bod Pod) in which the subject stands in water or Pod) in which the subject stands in water or sits in air.sits in air.


Plethysmography


Plethysmography

• The volume of the subject is determined by The volume of the subject is determined by measuring pressure changes produced by a measuring pressure changes produced by a pump.pump.

• The Bod Pod uses a pressure-volume The Bod Pod uses a pressure-volume relationship between two chambers to relationship between two chambers to estimate body volume.estimate body volume.


Plethysmography


Plethysmography

• Plethysmography is based on a combination Plethysmography is based on a combination of Boyle’s Law and Poisson’s Law.of Boyle’s Law and Poisson’s Law.

• They both relate to the inverse relationship They both relate to the inverse relationship between volume and pressure.between volume and pressure.


Plethysmography

• Boyle’s Law assumes isothermal conditions Boyle’s Law assumes isothermal conditions (air temperature remains constant as its (air temperature remains constant as its volume changes).volume changes).

• Poisson’s Law allows for changes in air Poisson’s Law allows for changes in air temperature as are found when the human temperature as are found when the human body gives off heat in an enclosed body gives off heat in an enclosed environment.environment.


Plethysmography

• It’s important to remember this difference It’s important to remember this difference because clothing, hair, thoracic gas volume, because clothing, hair, thoracic gas volume, and body surface area must be controlled and body surface area must be controlled since they act isothermically.since they act isothermically.


Plethysmography

• To control for these factors, clients are To control for these factors, clients are tested wearing minimal clothing (spandex tested wearing minimal clothing (spandex swimsuit) and a swim cap to compress the swimsuit) and a swim cap to compress the hair.hair.


Plethysmography

• An estimate of body surface area, calculated An estimate of body surface area, calculated from the height and weight of the client, is from the height and weight of the client, is used to correct for the isothermal effects of used to correct for the isothermal effects of the body’s surface.the body’s surface.


Plethysmography

• Thoracic gas volume, or the volume of the Thoracic gas volume, or the volume of the air in the lungs and thorax, is either directly air in the lungs and thorax, is either directly measured or estimated by the Bod Pod to measured or estimated by the Bod Pod to account for the isothermal conditions in the account for the isothermal conditions in the lungs.lungs.


Plethysmography

• Compared to UWW, the Bod Pod has Compared to UWW, the Bod Pod has excellent validity, with 2C comparisons excellent validity, with 2C comparisons showing the Bod Pod to have a difference showing the Bod Pod to have a difference of only -0.3% body fat.of only -0.3% body fat.


Bottle Buoyancy

• Involves having a subject hold a bottle Involves having a subject hold a bottle filled with water and air against their chest filled with water and air against their chest and submerge in a pool.and submerge in a pool.

• Water is added until the subject is Water is added until the subject is completely submerged and suspended just completely submerged and suspended just below the water surface.below the water surface.

• Once this occurs, the water in the bottle is Once this occurs, the water in the bottle is measured and volume calculated.measured and volume calculated.


Recommended Procedures

• Based on considerations of expense and the Based on considerations of expense and the precision and accuracy of measurement, the precision and accuracy of measurement, the underwater weighing technique continues to underwater weighing technique continues to be the most wide-spread and useful method be the most wide-spread and useful method for estimating body volume leading to the for estimating body volume leading to the assessment of body composition.assessment of body composition.

body composition assessment

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