Final - Body Composition Methodology

Question 1

Body composition assessment is quantification of what body structure components?

Answer 1

muscle (protein)
bone
fat
water (body fluid compartments)

Question 2

Overweight

Answer 2

a body mass greater than some standard (usually for a given stature)

Question 3

Overfat

Answer 3

body fat greater than a standard for sex and age (requires body composition analysis)

Question 4

Is it possible to be overweight without being overfat?

Answer 4

yep

Question 5

Essential fat

Answer 5

bone marrow stores & stores in viscera and nerves 
- needed for normal function
- 3% in males
- 12% in females
Includes sex-specific fat

Question 6

Storage Fat

Answer 6

• accumulation of lipid in adipocytes
• nutritional reserve
• subcutaneous and visceral (intraperitoneal)

Question 7

Lean Body Mass (LBM)

Answer 7

includes essential fat, muscle, water, bone, mineral

Question 8

Fat-Free Mass

Answer 8

All lipid contributions excluded

Question 9

BMI and obesity classification

Answer 9

20-24.9: desirable
25-29.9: Overweight (grade 1 obesity)
30-40: Grade 2 obesity
>40: grade 3 obesity

Question 10

Average % fat in young adults:

Answer 10

Men: 12-15%
Women: 25-28%

Question 11

Overview of Body Composition Methodologies

Answer 11

• Hydrostatic weighing
• Skinfolds
• Bioelectric Impedance Analysis
• Imaging Technologies
• Air Displacement Plethysmography (bod-pod)

Question 12

Overview of Densitometry

Answer 12

Measure Body Volume (hydrostatic weighing, skin folds, bod-pod) + measure body mass on a scale
mass/volume = density
conversion equation from density to %fat (Siri, Brozek)
Yields estimate of % fat

Question 13

Hydrostatic Weighing

Answer 13

• 2 compartment body composition model of FFM and fat
• Goal: estimate body density (d=m/v)
• We have mass, we need body volume

Question 14

Body Density

Answer 14

g/cm3 (mass per unit volume)

Question 15

Fat and FFM have different densities

Answer 15

• Fat-free body tissue: 1.100 g/cm3

- fat in adipose tissue: 0.900 g/cm3

Question 16

How does hydrostatic weighing work?

Answer 16

• determines body volume by Archimedes’ principle
• object placed in water is buoyed up by a counterforce equal to the water it displaces
• Amount of water displaced (spillover) equals loss of weight completely submerged

Question 17

When using hydrostatic weighing, what must you taken into account?

Answer 17

air in lungs and GI tract

failture will overpredict %fat

Question 18

Calculation of body density from underwater weight

Question 19

Population specific formulas to calculate % body fat from body density all have some error bc of biological variability

Answer 19

• bone mineral density
• partitioning and volume of water
• mineral components of the FFM

Question 20

Siri’s Equation

Answer 20

% body fat = (495/D) - 450

Question 21

Brozek’s Equation

Answer 21

% fat = (457/D) - 414.2

Question 22

Hydrostatic Weighing Validity

Answer 22

when residual volume is actually measured, hydrostatic weighing is the standard to which other methods are compared (within 2.0% of true value)

Question 23

Advantages of hydrostatic weighing

Answer 23

• highly reproducible
• can be highly accurate
• valid for many populations (except small children and those who won’t be submerged)

Question 24

Disadvantages of Hydrostatic Weighing

Answer 24

• best accuracy in highly technical experienced labs
• bulky equipment
• methodological concerns (prediction of RV, accuracy of weighing procedure, subject cooperation)

Question 25

Skinfold Thickness Anthropometric Measurement

Answer 25

- relies on the observation that within a certain population, a certain fraction of total body fat lies just under the skin (prediction of total body fatness from subcutaneous fat) - skin fold thickness highly correlated with % body fat

Question 26

Most important variables contributing to measurement error in Skinfold measurements

Answer 26

investigate technique and experience | reproducibility and accuracy

Question 27

Methodology for Skinfolds

Answer 27

- sites can vary (triceps, subscap, suprailiac, abdominal, thigh, chest) - Measurement duration is very important - reading should be taken within 2 seconds of applying caliper jaws

Question 28

Skinfold Caliper

Answer 28

Best results are obtained with a specifically- calibrated skin fold caliper - constant tension exerted by spring loaded caliper jaws - tension exerted affects how much extracellular fluid is pushed out of the area

Question 29

Prediction equations for skin folds

Answer 29

- choose equation develop and verified for subjects demographic - subcutaneous fat to total body fat ratio is altered with age and sex - failure to use appropriate equations can introduce huge errors into the estimate of density and % BF

Question 30

Sum of Skinfolds

Answer 30

- helpful for following weightless in an individual | - in obese individuals, it may be more accurate to use prediction equations that use circumferences than skin folds

Question 31

Advantages of Skinfolds

Answer 31

- inexpensive and quick - mass screening - good for following changes in body comp - fairly reproducible and accurate in experienced hands

Question 32

disadvantages of skin folds

Answer 32

- population specificity in prediction equations can lead to large error - error highly dependent on investigator technique - caliper used should be the same used in prediction equation

Question 33

Bioelectrical Impedance Analysis

Answer 33

- noninvasive, fast, accessible, relatively cheap method to evaluate body composition - determines electrical impedance of body tissues (measures opposition of tissues to flow of small alternating electrical current and provides estimate of total body water) - less impedance in FFM (due to greater electrolyte concentration)

Question 34

BIA estimates FFM and body fat from TBW from predication equations that use what?

Answer 34

- impedance - weight - height - sex - age

Question 35

BIA accuracy

Answer 35

- reliable estimate of TBW under most conditions - limited ability to predict body fat in severely obese - not useful in measuring short-term changes in body composition - significant differences in % fat prediction between manufacturers - different prediction equations used - accuracy equivalent to skin fold technique if protocol is followed

Question 36

Standard recommendations for BIA

Answer 36

- attempt to maintain normal hydration, plasma osmolality, body fluid distribution - dry skin - no eating/drinking within 4 hrs, exercise within 12 hrs, alcohol within 48 hrs, diuretic agents - void before assessment

Question 37

Near-Infrared Interactance

Answer 37

- uses amount of light absorption vs reflection: typically at a single site to predict body fat, uses prediction equations - not for human body composition analysis currently

Question 38

Air-Displacement Plethysmography (Bod-Pod)

Answer 38

- similar to hydrostatic weighing, it is densitometric - body volume directly measured - body density and % body fat calculated using same equations used to HW

Question 39

Bod Pod vs Underwater Weighing Advantages:

Answer 39

- Fast (5 mins) - Can use with various populations (obese, elderly, pediatric) - Good compliance ( no need for maximal exhalation or immersion, mobile) - less operator training required

Question 40

Body Composition Assessment Sources of Error:

Answer 40

- measurement error (intra and inter-investigator error) - subjectivity (training and experience) - fixed equipment or machine error - Underlying assumptions error (constants, models and predictive equations used, estimates of physiological variables, **normal biological variability) - experimental conditions (hydration status, subject cooperation, environment)