1. Assessment of Body Composition
David L. Gee, PhD
FCSN Nutrition Assessment Laboratory

2. Body Composition Analysis vs. Body Weight Assessment
Advantages
“Direct” assessment of body fatness
Overweight
Overmuscled or overfat
Athletes
Assessing need for weight loss
inadequate stores in patients
Monitor changes
weight loss quality
effect of medical therapy

3. Body Composition Analysis vs. Body Weight Assessment
Disadvantages
relatively limited database
all field methods are estimations
false assumptions in all field methods
errors by technicians
limited understanding by clients

4. Nutrition and Athletic Performance ACSM/ADA 2000 Position Paper
“Body fat assessment techniques have inherent variability, thus limiting the precision with which they can be interpreted.”
“With carefully applied skin-fold or BIA,…
relative body fat % error of 3% - 4%
15% (12-18%)
estimate fat-free mass within kg
50kg ( kg)
Would you buy a bathroom scale with this type of accuracy?
110 pounds + 7 pounds

5. Models of body composition
2 compartment models
Fat mass and Fat-free mass
Fat mass and Lean body mass
LBM includes cell membranes, TG in cells
assessment methods using this model
skinfold thickness
hydrodensitometry
bioelectric impedance

6. Models of body composition
4 compartment models
water, protein, fat , minerals
Assessment methods using this model
isotope dilution
dual emmision x-ray absorptiometry (DEXA)
computed tomography (CT, CAT)
Research techniques
Not covered in this course

7. Skinfold Thickness Advantages:
measures double thickness of skin and subcutaneous fat
Advantages:
inexpensive
fast
portable
large database

9. Skinfold Thickness Assumptions: predicts non-subcutaneous fat
>50% of fat is subcutaneous
sites selected represent average thickness of all subcutaneous fat
compressibility of fat similar between subjects
thickness of skin negligible

10. Skinfold Thickness Limitations Technician error
Skinfold thickness affected by factors other than amount of fat
exercise increases skin thickness
dehydration reduces skin thickness
edema increases skin thickness
dermatitis increases skin thickness
Poorly predicts visceral fat

12. Single Site Measurements
Tricep skinfold thickness
Subscapular skinfold thickness
not for estimating body fat determination
for comparing against other reference data
NHANES II ( )
appendix O (p ) (TSF)
appendix P (p ) (SSF)

13. Two site measurements Tricep SF and Subscapular SF
correlated with body fatness in children
fig (p192)
Tricep SF and calf SF
fig (p 192)

15. Multiple Site Measurements
many sites
many equations
table 6-9 (p193) Jackson & Pollock
table 6-10 (p193) Durnin & Womersley
density and %body fat
Siri
% BF = (495/BD) – 450
Brozek
% BF = (457/BD) - 414

18. Circumference Measurements Katch and McArdle
Principle:
measure two “fat” sites
measure one “muscle site”
estimate fat and lean body mass.
Very limited database
Easy to do

19. Hydrodensitometry

20. Hydrodensitometry Principle: two compartment model
density related to relative amounts of two compartments
D(fat) = 0.90 g/ml
D(lbm) = 1.10 g/ml
D(water) = 1.00 g/ml

21. Hydrodensitometry Density = Body weight/Body volume
How does one estimate body volume?
Archimedes principles:
volume of submerged object = volume of water displaced
weight in air - weight underwater = weight of water displaced

22. Hydrodensitometry calculate %BF from BD To calculate body density
wt of water displaced = vol of water displaced
Wt of water displaced = vol of body (BV)
Since weight of water displaced = weight in air - weight underwater
BV = BW-UBW
To calculate body density
BD = BW / BV
calculate %BF from BD

24. Hydrodensitometry Calculations
DATA
BW(air) = 180 lbs = 81.6 kg
BW(water) = UWW = 3.6 kg
RV = 1.30 L, est GI gas vol = 0.1 L
Density of 77 deg = kg/L
CALCULATIONS
BV = (BW-UWW)/.997 – (RV +0.1)
BV = ( )/.997 – ( )
BV = – 1.4 = L

25. Hydrodensitometry Calculations
BV = L
BD = BW / BV = 81.6/76.83 = kg/L
% BF = (495/BD)- 450 = (495/1.062)-450
%BF = = 16.09% = 16%
Fat mass = 16% x 81.6kg = 13.1 kg
Lean mass = = 68.5 kg

26. Hydrodensitometry: Assumption
Density of fat and lean are constant
bone density
muscle density
hydration status
GI gas volume is constant

27. Hydrodensitometry: Limitations
Measurement of residual lung volume
Precision of underwater weight
Cost
Non-portable
Limited types of subjects

29. Whole Body Pethysmography
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
results in bigger increase in pressure with injection of known volume of air

31. Whole Body Pethysmography
Advantages over hydrodensitometry
subject acceptability
precision
residual lung volume not factor
Limitations
costs: $25-30K
still assumes constant density of lean and fat

32. Bioelectrical Impedance Analysis
1994 NIH Technology Assessment Conference
“BIA provides a reliable estimate of total body water under most conditions.”
“It can be a useful technique for body composition assessment in healthy individuals”

33. 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)

34. 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

35. BIA: basic theory
Volume is equal to length of the cylinder times its area
Therefore, knowing the resistance and the length, one can calculate volume.
Assuming that the current flows thru the path of least resistance (water) , then the volume determined is that of body water.

36. BIA: basic theory
Assume fat free mass has a constant proportion of water (about 73%)
Then calculate fat free mass from body water
Assume BW = FFM + FM
Then calculate fat mass and %body fat

37. NHANES III BIA Equations
Males
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

38. BIA Calculations DATA CALCULATIONS R = 520 ohms BW = 170 lbs = 77.3 kg
H = 70” = 178 cm
CALCULATIONS
FFM = (0.65H2/R)+0.26W+0.02R
FFM = (0.65x1782/520)+0.26(77.3)+0.02(520)
FFM = = 59.5 kg
FM = W – FFM = 77.3 – 59.5 = 17.8 kg
%BF = (17.8/77.3)x100 = 23%

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

40. Major types of BIA analyzers

42. 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

43. What is a ‘normal’ % body fat?
Classification
Males
Females
Unhealthy range (too low)
< 5%
< 8%
Acceptable range (lower end)
6-15%
9-23%
Acceptable range (higher end)
16-24%
24-31%
Unhealthy (too high)
> 25%
> 32%
Nieman, (p195)

44. Body Composition Data NHANES III – 1988-1994
All adults > 19 yrs
Mean % Body Fat
Men: 21.9% % (SD)
Women: 32.4% %
Mean BMI
Men:
Women:
Mean waist circumference
Men: cm (cutpoint > cm)
Women: cm (> 89 cm)

45. Body Composition Data NHANES III – 1988-1994
Adults with BMI =
Mean % Body Fat
Men: 17.6% + 7.8% (SD)
Women: 26.7% + 8.9%
Mean BMI
Men:
Women:
Mean waist circumference
Men: cm (cutpoint > cm)
Women: cm (> 89 cm)

46. Dual-Energy X-ray Absorptiometry

47. DEXA, DXA Two different energy level X-rays
Lean, fat, and bone mass each reduce (attenuate) the X-ray signal in unique ways
Computer analyzes scan point by point to determine body composition
Method
Low dose radiation
20-30 minutes
Applicable to young and old