Body Composition Techniques

DIRECT ASSESSMENT The only direct methods for body composition assessment

are dissection or chemical analysis Brussels Cadavre Study

– 13 female and 12 male cadavers, age range 55–94 years, 12 embalmed and 13 unembalmed

– After comprehensive anthropometry, each cadaver was dissected into skin, adipose tissue, muscle, bones, organs and viscera.

– Volumes and densities of all tissues were determined by weighing the tissues underwater.

– A complete dissection lasted from 10 to 15 h and required a team of about 12 people.

Indirect or Doubly Indirect estimation of % Body Fat

All the techniques used routinely for % Body Fat estimation are either:– Indirect

% body fat is estimated using one or more assumptions e.g. Underwater Weighing

– Doubly Indirect% body fat is estimated by predicting the

results of an Indirect methodology from a related measure by regression analysis e.g. Skinfold prediction equations

Indirect Methods for the Estimation of % Body Fat

DENSITOMETRY

BODY DENSITY = MASS / VOLUMEUnits: gm/ml

Any method that determines the volume of the body is a densitometric method

“GOLD STANDARD”

Densitometry via underwater weighing was the “gold standard” for determination of % body fat since the 1940’s. Since the late 1990’s a 4 compartment method is regarded as the best reference method.

Body Density can be determined accurately Unfortunately, % Body Fat can not because of

assumptions made in transforming density to % Fat

DENSITOMETRY

Volumetry by WaterUnderwater (Hydrostatic) WeighingHelium DilutionBodPod – Whole Body Plethysmography

Predicting % Fat from Density

ASSUMPTIONSBody can be divided into two components:

Fat & Non-Fat (Fat Free) MassesEach has different, known and constant densities

Fat is not Adipose Tissue

FAT is ether extractable lipid molecules

ADIPOSE TISSUE is a tissue designed to store FAT (lipid) in adipocytes. Contains all the components of a tissue: cellular structures, extracellular matrix, water etc. as well as FAT (lipid) in the adipocytes. Adipose tissue is found subcutaneously and internally

SIRI EQUATION

Assumed Densities:FAT MASS 0.9 gm/mlNON-FAT (FAT FREE) MASS 1.1 gm/mlEquation:

% Body Fat = (4.95/Density) - 4.5) x 100

Siri Equation: % Fat = (4.95/Density)-4.5) x 100

BROZEK EQUATION

Assumptions:FAT MASS 0.9 gm/mlLEAN BODY MASS 1.095 gm/ml(some essential lipids in Lean Body Mass)

Equation:

% Fat = (4.57/Density)-4.142) x 100

DENSITOMETRYVolumetry by Water

Determine body volume by displacing water and directly measuring the change in water volume

DENSITOMETRYVolumetry by Water

 

Where:Wa = Body Weight in AirVwater displaced = Measured Volume of water displaced by the BodyRV = Residual VolumeC = Estimate of volume of entrapped intestinal gas

Archimedes (287-212 BC)

King Heiro of Syracuse summoned him to test the composition of a supposedly gold wreathIf assumed to be an alloy of only Gold and Silver he could use the laws of bouyancy to determine the fractional compositionPure Gold and Silver have constant and different densities

use Archimedes’ principle to determine body volume by calculating weight of water displaced

DENSITOMETRYUnderwater Weighing

Small Tank or Open Swimming Pool

use Archimedes’ principle to determine body volume by calculating weight of water displaced

DENSITOMETRYUnderwater Weighing

 

Where:Wa = Body Weight in AirWw= Body Weight freely submerged in waterDw = Density of water RV = Residual VolumeC = Estimate of volume of entrapped intestinal gas

Doubly Indirect Methods for the Estimation of % Body Fat

General Research Approachfor Doubly Indirect Methodologies

Selected subject sample based upon required criteria. Equations produced will be highly sample specific.

Determine body density or % fat of each subject using an accepted indirect methodology; often underwater weighing

Measure subjects with new predictor measure Produce regression equations to best predict density or

% fat from new predictor measure Equations often also include height, weight and activity

level and are age and sex specific

Regression Equations to Predict % Body Fat

d

Y

X

% Body Fat from Indirect Method = m(New Predictor Variable Measures) + c

Regression Analysis produces: m = slope, c= intercept Correlation Coefficient (r) Standard Error of Estimate (SEE in units of Y)

% Body Fat from Indirect Method

New Predictor Variable Measures

Doubly Indirect Methodsfor Estimating % Body Fat

Skinfold (Anthropometric) predictions Ultrasound Radiography Bioelectrical Impedance Analysis (BIA) Near-infrared Spectrophotometry (NIR) DEXA (Dual Energy X-Ray Absorptiometry)

There are no constants that can be applied to these predictor variables that will give a prediction of % Fat. They are all doubly indirect methodologies

Anthropometric (skinfolds)prediction of % Fat

Adipose Tissue not Fat Equations predict % Fat (Lipid) Over 100 equations available for the prediction of percentage body

fat or body density All are sample specific Specific for age, gender, activity level, nutrition etc.

Adipose Tissue

Assumptions inherent in prediction of % Fat from Skinfolds

Based upon densitometry

“Which is better UW Weighing or Skinfold predictions?”

%fat from skinfolds is predicted using equations developed from UW Weighing of subjects.

UW Weighing: S.E.E. = 2.77% Fat Skinfolds: S.E.E. = 3.7% Fat

Assumptions inherent in prediction of % Fat from Skinfolds

Constant Skinfold Patterning

Constant Skinfold Compressibility

Constant Tissue Densities

Constant Ratio of external/internal adipose tissue

Constant Fat (lipid) content of adipose tissue

YUHASZ

Male: % Fat = 0.1051(Sum 6 SF) + 2.585

Female: % Fat = 0.1548(Sum 6 SF) + 3.580

Canadian University Students

Can never give a negative answer.

What if weight alone changes or is different?

Durnin & Womersley

Density = a (log10Sum 4 SF) + c Overpredicts by 3 - 5% Fat British (left side) Age and gender specific equations Upper body sites Electronic Skinfold Caliper

Dual-Energy X-ray Absorptiometry

DEXA, DXADual Energy X-ray Absorptiometry

Two different energy level X-rays Lean, fat, and bone mass each reduce

(attenuate) the X-ray signal in unique ways Whole body Regional Osteoporosis

BMI = 12.6%Fat = 3.2%

BMI = 23.7%Fat = 48.1%

BMI = 18.1%Fat = 23.1%

What DEXA Measures

Fat and fat-free mass (based upon the standards)

Bone Mineral Mass Regional results for the above

DEXA Cannot Measure...

Protein Mass 3-D Fat Distribution Hydration Status Tissue inside bone (brain, marrow,

blood)

Next generation of Body Composition Models

Two compartment plus– Water– Bone mineral– Protein

3 or 4 compartment models now regarded as the reference standard rather than underwater weighing