Body Composition Chapter 4 Body Composition The relative
Body Composition Chapter 4 .
Body Composition • The relative proportion of fat and fat-free tissue in the body • Body composition is not determined by body weight per se, but what the weight is composed of • Most commonly uses the 2 -compartment model
Confusing Terminology • Overweight- deviation in body weight from some standard in relation to height • Overfat- body fat greater than some standard (BMI ≥ 25) • Obesity- higher amounts of fat that detrimentally affects health (BMI ≥ 30)
Health Consequences of Obesity • • Coronary Heart Disease Hypertension Type II Diabetes Hyperlipidemia Cancers Orthopedic problems Poor self-image
Body Composition Terminology • Fat weight (FW)- total fat amount in pounds • % fat- percentage of total body weight that is fat weight • Fat-free weight (FFW) – total fat-free tissue in pounds • % fat-free- percentage of total body weight that is fat-free tissue
Fat Weight + Fat-Free Weight = Body Weight % Fat + % Fat Free = 100%
Computational Example • Weight = 200 lbs; % fat = 20%; • Fat Weight = 200 x. 20 = 40 lbs • Fat-Free Weight = 200 - 40 = 160 lbs
Computing Ideal Weight • Ideal Weight = FFW / Ideal % FFW • Example – Body Wt = 180; %fat = 20%; What is ideal body weight at 10% fat? – FW = 180 lbs x. 20 = 36 lbs – FFW = 180 - 36 = 144 lbs – IBW = 144 /. 90 = 160 lbs
Components of Fat-Free Weight • Muscle • Bone • Organ Systems
Components of Fat Weight • Essential Fat – most is non-visible – associated with deeper body structures • Non-essential or Storage Fat – Beneath the skin and visible – Adipose tissue fat
Gender Differences In Body Fatness Gender Differences in Body Composition Male Body Weight 170 % Fat 15 Essential Fat 3% Non –Essential 12% Fat Female 130 25 12% 13%
Gender Differences • Females are proportionately fatter than males (as % of body mass) – Female sex hormones promote fat deposition – Male sex hormones promote muscle growth • Most of the female’s increase in fatness is due to an increase in the essential fat stores • Males and females have similar levels of nonessential fat
Quantification of Body Composition • • Height/Weight Ratio Body Mass Index (BMI), Quetelet Index Body density or % fat Waist to Hip Ratio
Height/Weight Ratio • Subjective measure • Assumes an average proportion of weight is fat • May incorporate frame size • Not a very desirable method
Body Mass Index • Weight/Height 2 ; kg/meters 2 • Extensively used in epidemiology studies • Most commonly used measure to define obesity • Does not measure fatness
Problems With BMI • • Weight = 280 lbs Height = 77 inches %fat = 30% (obese) BMI = 33 (obese) • • Weight = 280 lbs Height = 77 inches %fat = 15% (healthy) BMI = 33 (obese)
Waist/Hip Ratio • Waist circumference/Hip circumference • Waist- smallest circumference between the umbilicus and xiphoid process • Hip – largest circumference around the buttocks • Implication is that as waist get bigger there is more abdominal storage fat
Density and % Fat • Hydrodensitometry – (Underwater Weighing) – Hydrostatic Weighing • Air Displacement Plethysmography • Anthropometry – Skinfolds – Circumferences & Diameters • Bioelectrical Impedance
Hydrodensitometry (UWW) • Measures body volume using Archimedes' principle • Loss of weight in water is equal to the weight of the volume of water displaced • Density = mass or weight/volume
• Advantages of Hydrodensitometry – One of the most accurate methods • Disadvantages of Hydrodensitometry – Very subject dependent – Takes 15 minutes – Requires the ability to submerge subject under water – High skill required of technician
Plethsmyography (Bod Pod) • Body volume is determined by using Boyle’s Law – volume is inversely proportional to pressure. • Bod Pod measures pressure differences. • Density = mass or weight/volume
• Advantages of Plethysmography – Good accuracy – Little requirement from subject so good for children and older adults – Takes 5 minutes – Low skill required of technicial • Disadvantages of Plethysmography – Cost of equipment is $30, 000
Skinfolds • Based on the principle that subcutaneous fat at various locations (ie. The skinfolds) is predictive of total body fatness • Most equations use at least 2 skinfolds • Generally, the more skinfolds the more accurate the prediction of body fatness
• Advantages of Skinfolds – Subject has to do little – Many specific equations are available – Cost effective – Only takes 2 -3 minutes – Moderate accuracy • Disadvantages of Skinfolds – High technical skill required
Bioelectric Impedance Analysis (BIA) • Measures the resistance to a small electrical current introduced into the body (Impedance) • Once the impedance is determined then body water is determined. • Principle is that water is a good conductor and fat is a poor conductor of the electrical current. – More resistance = less body water = more fat – Less resistance = more body water = more muscle
• Advantages of BIA – Subject has to do little – Only need access to hand foot – Equipment is relatively inexpensive- $2000 – Moderate accuracy • Disadvantages of BIA – Highly dependent on hydration status
Interpreting % Fat Values • All methods of measuring % fat have a certain amount of inaccuracy! This inaccuracy is determined by the Standard Error of Estimate (SEE). • The SEE tells you the amount of deviation from the true % fat you can expect from a particular method.
• There is a 67% probability that the true % fat is within + or - one SEE from the measured value. • Example: Measure % fat = 20%; SEE = 3 % units of body fat There is a 67% probability that the true % fat is between + or - one SEE or 3 % units of fat. or between 17 - 23 %.
• There is a 95% probability that the true % fat is within + or - two SEE from the measured value. • Example: Measured %fat = 20% SEE = 3 % There is a 95% probability that the true %fat is within + or - two SEE or 6% of the measured value or 14 - 26 %.
SEE of Common Methods • • UWW – 1. 5 -2. 5% Plethysmography – 2. 2 -3. 7% Skinfolds – 3 -4% Bioelectric Impedance – Whole Body – 3 -4% – Segmental – 4 -6%
Healthy Values for %Fat • Reasonable & Healthy %fat Range – Males: 10 - 20% – Females: 15 - 30%
Computing UWW WT in air (kg) BD = Wt in air – WT in H 2 O Density H 2 O - RV (L) +0. 1
Converting Density to % Fat Siri Equation 495 %fat = Density - 450
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