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 = = 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 = = 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 Composition Gender Differences In Body Fatness MaleFemale Body Weight % Fat1525 Essential Fat3%12% Non –Essential Fat 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 non- essential 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 and 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 %.

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 %.

SEE of Common Methods UWW – % Plethysmography – % Skinfolds – 3-4% Bioelectric Impedance – Whole Body – 3-4% – Segmental – 4-6%

Healthy Values for %Fat Reasonable & Healthy %fat Range – Males: % – Females: %

Computing UWW BD = WT in air (kg) Wt in air – WT in H 2 O Density H 2 O RV (L)

Converting Density to % Fat Siri Equation %fat = 495 Density - 450