1. Chapter 15 Estimating Body Composition

2. What is Body Composition? Refers to the relative amounts of the different compounds in the body Why Study Body Composition?  Overweight vs. Over fat vs. Obesity  Risk for various diseases  Monitor change from an intervention  Some job requirements involve body composition standards  Athletic/sports prowess

3. Body Mass Index (BMI) The ratio of mass to height 2 BMI = body mass (kg) / body height (m) 2 for example BMI = 80 (kg) / 1.7 2 (m) = 27.68 kg/m 2 BMI < 20.0 is considered underweight (see Table 15.2) A BMI > 30 is associated with greater prevalence of mortality from heart disease, cancer, and diabetes

4. Low risk Moderate risk High risk Desirable Range for adults Grade I Obesity Grade II Obesity Grade III Obesity

5. Understanding Body Fat Fat Body Mass (FBM)- includes both essential and storage fat Essential Fat - found in bone marrow, the brain and spinal cord, muscles, and other internal organs. Approximates 3% of total body weight for men Approximates 3% of total body weight for women Storage Fat - 99% is yellow (adipose tissue) fat 1% is brown fat Lean Body Mass (LBM) - includes fat free body mass and essential fat Fat Free Body Mass (FFBM) - all body tissue excluding lipid and fat. However, LBM is used synonymously.

6. Ideal Weight The weight that would result from desired values for FBM and FFBM for example Fat weight = current weight (kg) x (% fat/100) Lean Body Mass = current weight (kg) - fat weight Ideal weight = LBM / [1 - (% fat desired / 100)] Desirable fat loss = current weight - ideal body weight

7. The Two-Component System of Body Composition This is the historical/traditional system for body composition assessment and quantification. m Lean Body Mass ( more accurately the FFBM) m Fat Body Mass The two component system has the following assumptions: 1. Fat density = 0.90 g/mL at 37  C 2. LBM density = 1.10 g/mL at 37  C 3. All individuals have the above mass densities 4. LBM is 73.8% water, 19.4% protein, and 6.8% mineral

8. FBM LBM Lean Tissue Body Water Model Fat Free Body MassMineral The Compartmental Models of Body Composition

9. Methods for the Two Component Model  Hydrodensitometry  Air-displacement plethysmography (BodPod  ) Hydrodensitometry (underwater weighing or hydrostatic weighing) Has been termed the “gold standard” of body composition assessment. However, inadequacies of the assumptions can cause errors as large as  4% fat. This method is based on Archimedes’ principle, where a person’s weight underwater is used to calculate body volume. Body density is then calculated, and specific equations are used that convert body density into %fat.

10. autopsy scale Strain gauges Analogue signal integration to computer chair platform Underwater weighing tank

11. Body Density (Db) = body mass (g) / body volume (mL) Db = Wa / {[(Wa - Ww) / Dw] - (RV + 100 mL)} where; Db = body density (g/mL) Wa = body mass out of water Ww = body mass underwater Dw = density of water (g/mL) RV = residual lung volume (mL) Siri Equation - % body fat = [(4.95 / Db) - 4.50] x 100 Brozek Equation - % body fat = [(4.57 / Db) - 4.142] x 100

12. Alternative equations to those of Siri and Brozek

13. Other Methods Skinfolds Dual X-Ray Absorptiometry (DEXA) Bioelectrical Impedance Near-Infrared Interactance