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Body Composition Techniques

Body Composition Techniques. 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

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Body Composition Techniques

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  1. Body Composition Techniques

  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.

  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 Fat

  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

  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

  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. SIRI EQUATION Assumed Densities: FAT MASS 0.9 gm/ml NON-FAT (FAT FREE) MASS 1.1 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 Assumptions: FAT MASS 0.9 gm/ml LEAN BODY MASS 1.095 gm/ml (some essential lipids in Lean Body Mass) Equation: % Fat = (4.57/Density)-4.142) x 100

  13. DENSITOMETRYVolumetry by Water Determine body volume by displacing water and directly measuring the change in water volume

  14. DENSITOMETRYVolumetry 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

  15. Archimedes (287-212 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

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

  17. DENSITOMETRYUnderwater 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

  18. DENSITOMETRYHelium Dilution • Densitometry • 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. DENSITOMETRYBODPOD - Whole Body Plethysmography

  20. DENSITOMETRYBODPOD - 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. DENSITOMETRYBODPOD - 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 Fat

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

  26. General Research Approachfor 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 Equationsto 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 • The pattern of deposition of skinfolds around the body is known to differ from individual to individual. • Females have characteristic deposition of secondary sexual adipose tissue on the upper arms, hips and thighs. • With ageing in both sexes there is a shift in dominance from limb to trunk deposition of adipose tissue

  31. Assumptions inherent in prediction of % Fat from Skinfolds • Constant Skinfold Compressibility • Skinfold compressibility varies from site to site due to differences in skin thickness, skin tension and adipose tissue composition. • Skinfolds in females are more compressible than in males. • Skinfold compressibility decreases with age due to dehydration and changes in elastic proprties of tissues

  32. Assumptions inherent in prediction of % Fat from Skinfolds • Constant Tissue Densities • Tissue densities vary greatly particularly that of bone. • 6 weeks of bed rest can cause a 2% loss in bone mineral.

  33. Assumptions inherent in prediction of % Fat from Skinfolds • Constant Ratio of external/internal adipose tissue • The ratio of external/internal adipose tissue varies with level of obesity • The ratio of external/internal adipose tissue declines with ageing.

  34. Assumptions inherent in prediction of % Fat from Skinfolds • Constant Fat (lipid) content of adipose tissue • Lipid content of adipose tissue varies from individual to individual due to variations in adipocyte size and number.

  35. YUHASZ Male: % Fat = 0.1051(Sum 6 SF) + 2.585 Female: % Fat = 0.1548(Sum 6 SF) + 3.580 Canadian University Students Can never give a negative answer. What if weight alone changes or is different?

  36. 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

  37. 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

  38. % 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

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

  40. 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

  41. 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)

  42. 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

  43. Typical BIA 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

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

  45. Major types of BIA analyzers

  46. Client Friendly

  47. Site Specific?

  48. 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

  49. 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

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