Body Composition Techniques

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Body Composition Techniques
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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 5594
  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.

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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

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Indirect Methods for the Estimation of Body Fat
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DENSITOMETRY
BODY DENSITY MASS / VOLUME Units gm/ml Any
method that determines the volume of the body is
a densitometric method
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GOLD STANDARD

• Densitometry via underwater weighing was the
  gold standard for determination of body fat
  since the 1940s. Since the late 1990s 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

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DENSITOMETRY
Volumetry by Water Underwater (Hydrostatic)
Weighing Helium Dilution BodPod Whole Body
Plethysmography
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Predicting Fat from Density
ASSUMPTIONS Body can be divided into two
components Fat Non-Fat (Fat Free) Masses Each
has different, known and constant densities
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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

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SIRI EQUATION
Assumed Densities FAT MASS 0.9 gm/ml NON-FAT
(FAT FREE) MASS 1.1 gm/ml Equation Body Fat
(4.95/Density) - 4.5) x 100
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Siri Equation Fat (4.95/Density)-4.5) x 100
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BROZEK EQUATION
Assumptions FAT MASS 0.9 gm/ml LEAN BODY MASS
1.095 gm/ml (some essential lipids in Lean Body
Mass) Equation Fat (4.57/Density)-4.142) x
100
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DENSITOMETRYVolumetry by Water
Determine body volume by displacing water and
directly measuring the change in water volume
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DENSITOMETRYVolumetry by Water
 
Where Wa Body Weight in Air Vwater displaced
Measured Volume of water displaced by the Body RV
Residual Volume C Estimate of volume of
entrapped intestinal gas
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Archimedes (287-212 BC)
King Heiro of Syracuse summoned him to test the
composition of a supposedly gold wreath If
assumed to be an alloy of only Gold and Silver he
could use the laws of bouyancy to determine the
fractional composition Pure Gold and Silver have
constant and different densities
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DENSITOMETRYUnderwater Weighing

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

Small Tank or Open Swimming Pool
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DENSITOMETRYUnderwater Weighing

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

 
Where Wa Body Weight in Air Ww Body Weight
freely submerged in water Dw Density of water
RV Residual Volume C Estimate of
volume of entrapped intestinal gas
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DENSITOMETRYHelium Dilution

• Densitometry
• Volume determined using a sealed chamber into
  which a known volume of Helium is introduced.
• Volume of air in chamber determined from dilution
  of Helium.
• Volume without subject determined (V1)
• Volume with subject determined (V2)
• Body Volume of Subject V1 V2
• Density Mass / Body Volume
• Fat from Siri or Brozek equation
• Does not require Residual Volume calculation

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DENSITOMETRYBODPOD - Whole Body Plethysmography
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DENSITOMETRYBODPOD - Whole Body Plethysmography

• Measures body volume by air displacement
• actually measures pressure changes with injection
  of known volume of air into closed chamber. Large
  body volume displaces air volume in chamber which
  results in bigger increase in pressure with
  injection of known volume of air
• Advantages over hydrodensitometry
• subject acceptability
• precision (reliability not accuracy)
• Limitations
• costs 25-30K
• still assumes constant density of FFM and fat for
  prediction of Body Fat from whole body density

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DENSITOMETRYBODPOD - Whole Body Plethysmography
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TOTAL BODY WATER (isotope dilution)

• Determined by introducing a marker fluid that
  moves freely in body water and is not
  metabolized.
• Isotopes of water - Deuterium Oxide, tritiated
  water
• Marker introduced.
• Following equilibriation period (eg 2 hrs) sample
  body fluid
• apply conversion formulae to estimate TBW,
• FAT predicted from TBW
• Assume a constant for the fraction of water in
  the Fat Free Mass or at least FFM (73.8, 72,3
  etc.)
• Even if no technical error in Body Water, there
  would still be S.E.E. 3.6 Body Fat associated
  with biological variability

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K40 - Whole Body Counting

• K40 emits gamma radiation
• Using whole body counters the amount of radiation
  emitted can be determined
• Fat Free Mass (Non-fat Mass) estimated
  Assumptions
• Constant fraction of K40 in potassium
• Constant fraction of potassium in non-fat mass

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Doubly Indirect Methods for the Estimation of
Body Fat
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Doubly Indirect Methodsfor Estimating Body Fat

• Skinfold predictions
• Ultrasound
• Radiography
• Bioelectrical Impedance Analysis (BIA)
• Near-infrared Spectrophotometry (NIR)
• DEXA

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General Research Approachfor Doubly Indirect
Methodologies

• Selected subject sample
• Determine body density or fat using an accepted
  methodology often underwater weighing
• Measure subjects with other technique
• Produce regression equations to best predict
  density or fat from new technique

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Regression Equationsto Predict Body Fat
Y mX c Y Body Fat X Anthropometric
measure (Skinfolds etc) Correlation Coefficient
(r) Standard Error of Estimate (SEE)
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Anthropometric (skinfolds)prediction of Fat
Adipose Tissue

• 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.

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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
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Assumptions inherent in prediction of Fat from
Skinfolds

• Constant Skinfold Patterning
• The pattern of deposition of skinfolds around the
  body is known to differ from individual to
  individual.
• Females have characteristic deposition of
  secondary sexual adipose tissue on the upper
  arms, hips and thighs.
• With ageing in both sexes there is a shift in
  dominance from limb to trunk deposition of
  adipose tissue

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Assumptions inherent in prediction of Fat from
Skinfolds

• Constant Skinfold Compressibility
• Skinfold compressibility varies from site to site
  due to differences in skin thickness, skin
  tension and adipose tissue composition.
• Skinfolds in females are more compressible than
  in males.
• Skinfold compressibility decreases with age due
  to dehydration and changes in elastic proprties
  of tissues

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Assumptions inherent in prediction of Fat from
Skinfolds

• Constant Tissue Densities
• Tissue densities vary greatly particularly that
  of bone.
• 6 weeks of bed rest can cause a 2 loss in bone
  mineral.

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Assumptions inherent in prediction of Fat from
Skinfolds

• Constant Ratio of external/internal adipose
  tissue
• The ratio of external/internal adipose tissue
  varies with level of obesity
• The ratio of external/internal adipose tissue
  declines with ageing.

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Assumptions inherent in prediction of Fat from
Skinfolds

• Constant Fat (lipid) content of adipose tissue
• Lipid content of adipose tissue varies from
  individual to individual due to variations in
  adipocyte size and number.

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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?
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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

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Ultrasound
High Frequency Sound (6 MHz) Some sound reflected
at tissue interfaces Time taken for return of
sound used to estimate distance based upon
assumed speed of sound in that tissue
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Fat prediction from Ultrasound

• Regression equations predicting densitometrically
  determined Fat
• S.E.E.s comparable to skinfold predictions
• Beware of predict anything from anything once
  it is in a computer

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RADIOGRAPHY

• Measurements from radiographs
• uncompressed tissue thicknesses
• Regression equations predicting densitometrically
  determined Fat

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BIOELECTRICAL IMPEDANCE ANALYSIS (BIA)

• BIA measured by passing a microcurrent through
  the body
• Fat predicted from sex, age, height, weight
  activity level BIA
• Influenced by hydration level
• Claims that you can guess fat more accurately

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Bioelectrical Impedance Analysis

• BIA measures impedance by body tissues to the
  flow of a small (lt1mA) alternating electrical
  current (50kHz)
• Impedance is a function of
• electrical resistance of tissue
• electrical capacitance (storage) of tissue
  (reactance)

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BIA basic theory

• The body can be considered to be a series of
  cylinders.
• Resistance is proportional to the length of the
  cylinder
• Resistance is inversely proportional to the
  cross-sectional area

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Typical BIA Equations

• Males
• FFM -10.68 0.65H2/R 0.26W 0.02R
• Females
• FFM -9.53 0.69H2/R 0.17W 0.02R
• Where
• FFM fat free mass (kg)
• H height (cm)
• W body weight (kg)
• R resistance (ohms)
• BF 100 x (BW-FFM)/BW

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BIA Advantages and Limitations

• Advantages
• costs (500-2000)
• portable
• non-invasive
• fast
• Limitations
• accuracy and precision
• no better, usually worse than hydrodensitometry

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Major types of BIA analyzers
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Client Friendly
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Site Specific?
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BIA Protocol

• Very sensitive to changes in body water
• normal hydration
• caffeine, dehydration, exercise, edema,
  fed/fasted
• Sensitive to body temperature
• Avoid exercise
• Sensitive to placement of electrodes
• conductor length vs. height

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Near Infra-Red Spectrophotometry (NIR)FUTREX

• Near Infra-Red light emitted from probe
• Reflected light monitored
• Changes due to differing optical densities
• Influenced by hydration
• Relative fat may be useful

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Infrared InteractanceConway et al. 1984
Reflected light has modified frequency
spectrum. SEE 3.0 bodyfat. The correlation
coefficients between body fat as predicted by
the IRI method and as estimated by the D20
dilution technique were 0.84,0.95, and 0.94 for
males, females, and males plus females, respective
ly (p lt 0.01 for all three values).
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Dual-Energy X-ray Absorptiometry
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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

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X-Ray Measurement System

• Dual energy attenuation values are measured for
  each point in the image
• Calibration standards (acrylic, aluminum, delrin)
  are measured
• The fat and lean mass of each point in the image
  is calculated by direct comparison to the
  standards

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BMI 12.6 Fat 3.2
BMI 23.7 Fat 48.1
BMI 18.1 Fat 23.1
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What DEXA Measures

• Fat and fat-free mass (based upon the standards)
• Bone Mineral Mass
• Regional results for the above

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DEXA Cannot Measure...

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

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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