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Assessment of Body Composition

Assessment of Body Composition. David L. Gee, PhD FCSN 442 - Nutrition Assessment Laboratory. Body Composition Analysis vs. Body Weight Assessment. Advantages “Direct” assessment of body fatness Overweight Overmuscled or overfat Athletes Assessing need for weight loss

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Assessment of Body Composition

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  1. Assessment of Body Composition David L. Gee, PhD FCSN 442 - 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 PerformanceACSM/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 2.5-3.5 kg • 50kg (47.5-52.5kg) • 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 • measures double thickness of skin and subcutaneous fat • Advantages: • inexpensive • fast • portable • large database

  8. 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

  9. 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

  10. Single Site Measurements • Tricep skinfold thickness • Subscapular skinfold thickness • not for estimating body fat determination • for comparing against other reference data • NHANES II (1097-1980) • appendix O (p530-532) (TSF) • appendix P (p533-535) (SSF)

  11. Two site measurements • Tricep SF and Subscapular SF • correlated with body fatness in children • fig. 6-32 (p192) • Tricep SF and calf SF • fig. 6-33 (p 192)

  12. 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

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

  14. Hydrodensitometry

  15. 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

  16. 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

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

  18. 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 water @ 77 deg = 0.997 kg/L • CALCULATIONS • BV = (BW-UWW)/.997 – (RV +0.1) • BV = (81.6-3.6)/.997 – (1.3+0.1) • BV = 78.23 – 1.4 = 76.83 L

  19. Hydrodensitometry Calculations • BV = 76.83 L • BD = BW / BV = 81.6/76.83 = 1.062 kg/L • % BF = (495/BD)- 450 = (495/1.062)-450 • %BF = 466.09-450 = 16.09% = 16% • Fat mass = 16% x 81.6kg = 13.1 kg • Lean mass = 81.6-13.1 = 68.5 kg

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

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

  22. 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

  23. 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

  24. 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”

  25. 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)

  26. 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

  27. 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.

  28. 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

  29. NHANES IIIBIA Equations • Males • FFM = -10.68 + 0.65H2/R + 0.26W + 0.02R • Females • FFM = -9.53 + 0.69H2/R + 0.17W + 0.02R • Where • FFM = fat free mass (kg) • H = height (cm) • W = body weight (kg) • R – resistance (ohms) • % BF = 100 x (BW-FFM)/BW

  30. BIA Calculations • DATA • R = 520 ohms • BW = 170 lbs = 77.3 kg • H = 70” = 178 cm • CALCULATIONS • FFM = -10.68+(0.65H2/R)+0.26W+0.02R • FFM = -10.68+(0.65x1782/520)+0.26(77.3)+0.02(520) • FFM = -10.6 + 39.6 + 20.1 + 10.4 = 59.5 kg • FM = W – FFM = 77.3 – 59.5 = 17.8 kg • %BF = (17.8/77.3)x100 = 23%

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

  32. Major types of BIA analyzers

  33. 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

  34. What is a ‘normal’ % body fat? Nieman, 1999 (p195)

  35. Body Composition DataNHANES III – 1988-1994 • All adults > 19 yrs • Mean % Body Fat • Men: 21.9% + 11.6% (SD) • Women: 32.4% + 17.8% • Mean BMI • Men: 26.5 + 7.8 • Women: 26.4 + 11.7 • Mean waist circumference • Men: 95.1 + 18.6 cm (cutpoint > 101.6 cm) • Women: 88.6 + 30.2 cm (> 89 cm)

  36. Body Composition DataNHANES III – 1988-1994 • Adults with BMI = 18.5-25 • Mean % Body Fat • Men: 17.6% + 7.8% (SD) • Women: 26.7% + 8.9% • Mean BMI • Men: 22.7 + 3.2 • Women: 22.0 + 2.2 • Mean waist circumference • Men: 84.7 + 8.9 cm (cutpoint > 101.6 cm) • Women: 78.0 + 13.4 cm (> 89 cm)

  37. Dual-Energy X-ray Absorptiometry

  38. 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

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