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