1. Body Composition Techniques1

2. 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. 2

3. 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

4. Indirect Methods for the Estimation of % Body Fat1

5. DENSITOMETRY BODY DENSITY = MASS / VOLUME Units: gm/ml
Any method that determines the volume of the body is a densitometric method

6. “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 3

7. DENSITOMETRY Volumetry by Water Underwater (Hydrostatic) Weighing
Helium Dilution
BodPod – Whole Body Plethysmography

8. 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 6

9. 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

10. % Body Fat = (4.95/Density) - 4.5) x 100
SIRI EQUATION
Assumed Densities:
FAT MASS gm/ml
NON-FAT (FAT FREE) MASS gm/ml
Equation:
% Body Fat = (4.95/Density) - 4.5) x 100

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

12. BROZEK EQUATION % Fat = (4.57/Density)-4.142) x 100 Assumptions:
FAT MASS gm/ml
LEAN BODY MASS gm/ml
(some essential lipids in Lean Body Mass)
Equation:
% Fat = (4.57/Density)-4.142) x 100

13. DENSITOMETRY Volumetry by Water
Determine body volume by displacing water and directly measuring the change in water volume 5

14. DENSITOMETRY Volumetry 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 5

15. Archimedes ( 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 6

16. DENSITOMETRY Underwater Weighing
use Archimedes’ principle to determine body volume by calculating weight of water displaced
Small Tank or Open Swimming Pool 5

17. DENSITOMETRY Underwater 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 5

18. DENSITOMETRY Helium Dilution
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

19. DENSITOMETRY BODPOD - Whole Body Plethysmography

20. DENSITOMETRY BODPOD - 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

21. DENSITOMETRY BODPOD - Whole Body Plethysmography

22. 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

23. 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

24. Doubly Indirect Methods for the Estimation of % Body Fat1

25. Doubly Indirect Methods for Estimating % Body Fat
Skinfold predictions
Ultrasound
Radiography
Bioelectrical Impedance Analysis (BIA)
Near-infrared Spectrophotometry (NIR)
DEXA

26. General Research Approach for 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

27. Regression Equations to Predict % Body Fat
Y = mX + c
Y = % Body Fat
X = Anthropometric measure (Skinfolds etc)
Correlation Coefficient (r)
Standard Error of Estimate (SEE)

28. 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.

29. 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

30. 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

31. YUHASZ Male: % Fat = 0.1051(Sum 6 SF) + 2.585
Female: % Fat = (Sum 6 SF)
Canadian University Students
Can never give a negative answer.
What if weight alone changes or is different?

32. 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

33. 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

34. % 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

35. RADIOGRAPHY Measurements from radiographs
uncompressed tissue thicknesses
Regression equations predicting densitometrically determined % Fat

36. 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

37. Bioelectrical Impedance Analysis
BIA measures impedance by body tissues to the flow of a small (<1mA) alternating electrical current (50kHz)
Impedance is a function of:
electrical resistance of tissue
electrical capacitance (storage) of tissue (reactance)

38. 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

39. Typical BIA Equations Males Females Where % BF = 100 x (BW-FFM)/BW
FFM = H2/R W R
Females
FFM = H2/R W R
Where
FFM = fat free mass (kg)
H = height (cm)
W = body weight (kg)
R – resistance (ohms)
% BF = 100 x (BW-FFM)/BW

40. BIA: Advantages and Limitations
costs ($500-$2000)
portable
non-invasive
fast
Limitations
accuracy and precision
no better, usually worse than hydrodensitometry

41. Major types of BIA analyzers

43. Client Friendly

44. Site Specific?

45. 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

46. 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

47. Dual-Energy X-ray Absorptiometry

48. DEXA, DXA Dual 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

49. 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

51. BMI = 12.6 %Fat = 3.2% BMI = 18.1 %Fat = 23.1% BMI = 23.7 %Fat = 48.1%
These are images from anorexic, normal, and obese subjects. The brightness of the image is proportional to material density. The bone is the most dense, followed by muscle, and then fat. The subcutaneous fat around the hips can be seen on the normal and obese subject.
BMI = 12.6
%Fat = 3.2%
BMI = 18.1
%Fat = 23.1%
BMI = 23.7
%Fat = 48.1%

52. What DEXA Measures Fat and fat-free mass (based upon the standards)
Bone Mineral Mass
Regional results for the above

53. DEXA Cannot Measure... Protein Mass 3-D Fat Distribution
Hydration Status
Tissue inside bone (brain, marrow, blood)

54. 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