Human Body Composition
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Transcript of Human Body Composition
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Human Body Composition
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We All Change in Many Ways
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Why is knowledge of body
composition so important?
Health and Disease
Nutritional Therapy
Growth Rate
Nutritional Requirements
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Methods of Body Composition
Direct Assessment
Chemical dissolution: dissolves body into fat
and fat-free components
Physical dissection: extensive dissection of
cadavers.
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Indirect Body Composition
Hydrostatic Weighing
Air Displacement
Skinfolds
Girth Measurements Bioelectrical Impedance
Analysis
Dual-Energy X-RayAbsorptiometry
Near InfraredInteractance
Ultrasound
Computed Tomography
Magnetic ResonanceImaging
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Underwater Weighing Technique
Body fat provides
more buoyancy so a
fatter person weighs
less (on a relative
basis) than a lean
person
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Technological Assessments
of Body Composition
Dual X-Ray Absorptiometry (DXA)
Bioelectric impedance
Infra-red spectroscopy
Ultrasound
Imaging techniques (DEXA, MRI)
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Skinfold Technique
Layers ofsubcutaneous
fat are measured at
different sites of body
to estimate total body
fat levels
Cross sectional view
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Benefits of Skinfold Technique
Fairly accurate
Easy to perform
Inexpensive
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Common Skinfold Sites
7 site procedureChest
Axilla
Tricep
Subscapular
Abdomen
Supraillium
Thigh
Jackson and Pollack
Males Female
Chest Triceps
Abdomen Supraillium
Thigh Thigh
Alternative Sites
(Males & Females)Tricep
Abdomen
Calf
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Research Quality
Skinfold Calipers
Harpenden Calipers
Lange Calipers
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Anthropometric Measurements
Body Mass Index (BMI)
Waist to Hip Ratio (WHR)
Circumference measures
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WHR Measurement Technique
Waist: Measure at the "natural waist" (smallestcircumference) or at the level of the umbilicus
Hip: Measure at the maximum circumferenceof the buttocks
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Waist to Hip Ratio (WHR)
Waist to Hip Ratio is an effective way to
examine regional fat distribution.
WOMENMEN
High Risk
Moderate Risk
Low Risk
> 1.0 > .85
.90 -1.0 .80-.85
HEALTH RISK
< .90 < .80
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Underwater WeighingMeasurement issues
Based on body density calculations Density of lean tissue = 1.1 g/cc
Density of fat tissue = .9 g/cc
Sources of error Residual lung volume
Bone density varies by age, ethnicity and activity level
General conclusions Gold standard measure (1-2% error)
Impractical for most applications
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Dual X-Ray Absorptiometry(DXA)
use of DXA devices.
Two distinct x-ray energies
penetrate into bone & soft tissueareas to depth of 30 cm. Computer
software reconstructs an image of
underlying tissue.
Quantifies bone mineral content,
total fat mass, and FFM.
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Bioelectric Impedence(Measurement Issues)
Based on resistance to current flow Lean tissue has more water - less resistance
Fat tissue has less water - more resistance
Sources of error Temperature
Hydration status
General conclusions Overestimates lean / underestimates obese
Practical, but expensive, measure for general
population
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Infrared Spectroscopy(Measurement Issues)
Based on differential absorbance rates Lean tissue has a different energy absorption and reflectance pattern
than fat tissue
Sources of error Validity of absorbance readings is questionable!
General findings NOT a valid measure!
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Ultrasound(Measurement Issues)
Based on reflection of sound Fat content increases the time is required for sound to reflect off of
bone and muscle.
Sources of error Representative sites for measurement
Measurement error
General conclusions Highly accurate measure of body fat - especially for obese
Expensive and not practical for most applications
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Imaging Techniques(Measurement Issues)
Based on imaging of body tissues Based on cross sectional area measures
calculated at different levels of the body
Sources of error Representative sites for measurement
Measurement error
General conclusions Very precise measure of body composition
Expensive and not practical measure for most uses
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Circumferences(Measurement Technique)
Based on circumference measures sample prediction equation:
% fat = - 47.372 + (.579 x abdomen) + (.252 x hip) + (.214 x iliac) + (.356 x BW)
Sources of error Location of sites
Inability to distinguish fat and muscle
General conclusions Provides reasonable estimate of body fat
Not as accurate as skinfold and takes same time
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Body Mass Index (BMI)
BMI = BW(kg) / HT2 (m2)
Where, BW = Body weight in kg
HT = Height in m
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Obesity Class BMI kg/m2
Underweight