Body Composition Techniques 1

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

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

Indirect Methods for the Estimation of % Body Fat 1

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

“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

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

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

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

% Body Fat = (4.95/Density) - 4.5) x 100 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

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

BROZEK EQUATION % Fat = (4.57/Density)-4.142) x 100 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

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

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

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 6

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

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

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

DENSITOMETRY BODPOD - Whole Body Plethysmography

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

DENSITOMETRY BODPOD - Whole Body Plethysmography

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

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

Doubly Indirect Methods for the Estimation of % Body Fat 1

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

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

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)

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.

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

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

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?

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

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

% 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

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

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

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)

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

Typical BIA Equations Males Females Where % BF = 100 x (BW-FFM)/BW 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

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

Major types of BIA analyzers

Client Friendly

Site Specific?

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

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

Dual-Energy X-ray Absorptiometry

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

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

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%

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

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

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