human body composition

7/28/2019 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

human body composition

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