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Chapter 12

Chapter 12. Evaluating Body Composition. Chapter 12 Outline. Public Health Risks Sources of Adulthood Obesity Anthropometric Assessments of Body Composition Evaluating Body Composition of Adults Screening Tool for Steroid Abuse - FFMI

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Chapter 12

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  1. Chapter 12 Evaluating Body Composition

  2. Chapter 12 Outline • Public Health Risks • Sources of Adulthood Obesity • Anthropometric Assessments of Body Composition • Evaluating Body Composition of Adults • Screening Tool for Steroid Abuse - FFMI • Skinfold Assessments of Percent fat of Children and Youth • Comparison of Body Composition Methods

  3. Definitions and Statistics • Overweight: Body mass index (BMI) 25 - 29.9 kg.m-2 • Obese: BMI  30 kg.m-2 • Percent Body Fat: Proportion of total weight that is fat. • Proportion of Americans who are overweight and obese is growing. • NHANES 1999-2002: 62% of women; 69% of men were overweight.

  4. Public Health Risks • Overweight: • increased risk of heart disease and stroke. • increased risk of breast cancer in post-menopausal. • Body fat percent that is too low provides health risks. • Intelligent application of assessment and education about body fat can help people establish desirable, intelligent weight goals.

  5. Sources of Adulthood Obesity • Consume more calories than expend. • Why some people gain weight while others do not? • Genetic? • Environmental? • Psychological? • Both parental obesity and being obese as a child and adolescent increase risk of adult obesity.

  6. Laboratory Body Composition Measures • Underwater weighing • Bod Pod • Dual energy X-ray absorptiometry (DXA)

  7. Underwater Weighing (Hydrostatic) • Popular lab method to measure body composition. • Objective is to measure body volume. • Body Density: ratio of body weight and body volume. Body Density = weight in air  body volume. • Percent fat is calculated from body density.

  8. Underwater Weighing (Hydrostatic) • Based on Archimedes’ Principle: • when an object is submerged in water, difference between weight in air and weight under water equals weight of the water displaced. • Weight of water displaced divided by density of water equals body volume.

  9. Steps to Determine Body Density • Determine underwater weight. • Determine land weight. • Determine air in the body. • Residual lung volume must be measured. • Largest potential source of error in underwater weighing technique. • Determine density of the water. • Based on temperature of water.

  10. Computing Body Volume (BV) BV = [(Weight – Weight W) Dw] – air in body where BV = Body Volume, Weight W = weight in water, Dw = density of water, air in body = residual volume + 100 ml.

  11. Computing Body Density • Body Density = Weight  Body Volume

  12. BODPOD • Body plethysmograph or body box. • Based on Boyle’s Law: • Pressure of a gas varies inversely with its volume. • Air volume in the box can be measured. • When person enters box, pressure changes and can measure new volume in box. • Very high correlation with underwater weighing. • Easier than underwater weighing for people uncomfortable in water.

  13. Converting Body Density to Percent Fat • Variation in body density is due to air, fat weight, and fat-free weight. • Density of air = 0. • Density of fat weight ~ 0.90 g/cc. • Density of fat-free weight ranges from ~ 1.0 to 3.0 g/cc. • mean assumed to be 1.10 g/cc

  14. Two-component Models • Make an assumption that density of fat tissue is 0.90 g/cc • Make assumption that density of fat-free tissue is a specific value: • 1.10 g/cc (Siri, Brozek), 1.113 g/cc (Schutte), 1.106 g/cc (Wagner, Ortiz) • Siri Percent Fat Equation: • %fat = (495  Body Density) – 450 • Brozek Percent Fat Equation: • %fat = (457  Body Density) – 414 • Schutte Percent Fat Equation (for African American males): • %fat = (437.4  Body Density) – 392.8 • Wagner Percent Fat Equation (for African American males) • %fat = (486  Body Density) – 439 • Ortiz Percent Fat Equation (for African American females) • %fat = (485  Body Density) - 439

  15. Four-component Models • Two-component model has limitations when measuring children, older adults, and some non-white ethnic groups. • Total body water and bone mineral content may vary from assumed values, which alter density of fat-free weight component. • Four-component model includes water and mineral content, along with body density.

  16. Four-component Percent Fat Model %fat = (2.749  Body Density) – (0.727 * w) – (1.146 * m) – 2.053 where w is water and m is mineral. Dual energy X-ray absorptiometry (DXA) technology can measure bone mineral content.

  17. Comparison of Two- and Four-component Models • Four-component model viewed as most accurate method. • Differences in percent fat estimates between two- and four-component models are not large.

  18. DXA • Participant lies on a table and a total body scan is conducted. • Scan divides non-bone tissue into fat and lean components. • Total body bone mineral mass • Bone-free lean tissue • Fat mass • Fat-free mass = total body bone mineral mass + bone-free lean tissue • Does not measure total body water. • Can assess regional body composition.

  19. Anthropometric Assessment of Body Composition • Body Mass Index (BMI) • Body Circumferences • Waist-Hip Ratio (WHR) • Skinfolds

  20. Body Mass Index (BMI) • BMI = weight (kg)  height2 (m) • weight (kg) = pounds  2.2 • height (m) = inches * 0.0254 • height2 (m) = height (m) * height (m) • Used in large-scale public health studies.

  21. World Health Organization Criteria for Overweight and Obesity by BMI Category BMI Underweight < 18.5 Normal Weight 18.5 – 24.9 Overweight 25.0 – 29.9 Obese Class I 30.0 – 34.9 Obese Class II 35.0 – 39.9 Obese Class III > 40

  22. Prediction of Percent Fat from BMIGallagher et al. (1996) %fat = (1.46 * BMI) + (0.14 * Age) - (11.61 * Gender) - 10.02 where Male = 1 and Female = 0. R = .81, SEE = 5.7%fat

  23. Prediction of Percent Fat from BMIJackson et al. (2002) %fat = (1.61 * BMI) + (0.13 * Age) - (12.11 * Gender) - 13.91 where Male = 1 and Female = 0. R = .75, SEE = 5.5%fat

  24. BMI Standards • BMI lacks accuracy when estimating %fat of individuals. • Does not take into account the quality of weight (i.e., fat vs. lean). • A BMI of 25 or 30 kg.m-2 does not correspond to same percent fat at different ages. • BMI of 25 kg.m-2 is a percent fat of about 20% for men and about 30% for women. • BMI of 30 kg.m-2 is a percent fat of about 27% for men and about 40% for women.

  25. Body Circumferences • Circumferences most highly correlated with percent fat are in abdomen and hip. • Percent fat estimated by circumferences is used by U.S. Navy.

  26. Waist-Hip Ratio (WHR) • People with central obesity are at high risk for CVD. • Central obesity often assessed by waist-hip ratio. • Waist circumference – at narrowest point between the umbilicus and xiphoid process. • Hip circumference – at largest circumference around buttocks. • Combination of BMI and WHR can be used to define health risk. • WHR may be better measure of obesity than BMI. • WHR more highly associated with heart attacks than BMI

  27. Waist-Hip Ratio (WHR) • As WHR increases, risk of heart attack increases. • Significantly increased risk of heart attack: • For men, WHR > 0.90 • For women, WHR > 0.83

  28. Types of Obesity • Android Obesity – central or upper body adiposity (apple-shaped). • Increased WHR indicative of android obesity • Android obesity = higher risk of heart attack • Gynoid Obesity – excess fat deposited in hips and thighs (pear-shaped). • Gynoid obesity = lower risk of heart attack

  29. Skinfolds • Highly correlated with body density from hydrostatic weighing. • Double thickness of subcutaneous fat is measured with calipers. • Need proper training to locate and measure skinfolds. • Improper site selection main reason for errors. • Measured on right side of body for standardization.

  30. Common Skinfold Sites • Chest • Axillary • Triceps • Subscapular • Abdomen • Suprailium • Thigh • Medial Calf

  31. Skinfold Measurement Methods • Pinch and pull skin with left hand (use thumb and index finger) and hold caliper in right hand. • Place caliper perpendicular to fold. • Place caliper ~ 1 cm (0.25 in.) from fingers. • Release caliper so full tension is exerted. • Read dial to nearest 0.5 mm ~ 1 to 2 seconds after releasing grip. • Take minimum of 2 measures. If they vary by more than 1 mm, take a third measure.

  32. Skinfold Measurement Methods • If consecutive pinches become smaller, the fat is being compressed. Go on to next site and return to trouble spot after taking other measures. • Final value is average of two that best represent skinfold site. • Typically, complete a measurement at one site before moving to another site. • Practice on 50 to 100 subjects.

  33. Skinfold Assessment ofPercent Fat of Adults • Generalized equations (Jackson-Pollock equations): • Developed on large, heterogeneous samples (18 to 61 years of age). • Separate equations are needed for men and women. • Equation for sum of three skinfolds is typically used. • Men: chest, abdomen, thigh • Women: triceps, suprailium, thigh

  34. Jackson-Pollock 3-Site Skinfold Equations Women: Body Density = 1.099421 - (0.0009928 * 3 skinfolds) - (0.00000023 * 3 skinfolds2) - (0.0001382 * Age) R = .84, SEE = 3.9%fat Siri, Brozek, Shutte, Wagner, or Ortiz equations can then be used to estimate percent fat.

  35. Jackson-Pollock 3-Site Skinfold Equations Men: Body Density = 1.10938 - (0.0008267 * 3 skinfolds) - (0.0000016 * 3 skinfolds2) - (0.0002574 * Age) R = .91, SEE = 3.5%fat Siri, Brozek, Shutte, Wagner, or Ortiz equations can then be used to estimate percent fat.

  36. Bioelectrical Impedance (BIA) • Based on principle that resistance to flow of electrical current through the body is related to total body water. • With traditional method, electrodes are placed on wrist and ankle. • Newer methods do not require electrodes.

  37. Bioelectrical Impedance (BIA) • Non-detectable (low level) electrical current is transmitted through the body. • Resistance to flow of the current is measured. • Accuracy is similar to skinfolds, except for obese and very lean people. • Accuracy of newer hand-to-hand and foot-to-foot analyzers lower than for whole-body BIA analyzers.

  38. Traditional BIA Measurement

  39. BIA Assessment Guidelines • No diuretic medications with a week of test • Avoid alcohol within 2 days of test • Avoid exercise within 12 hours of test • Avoid eating or drinking within 4 hours of test • Urinate within 30 minutes of test

  40. Evaluating Body Composition of Adults • Relationship between weight and all-cause mortality is J-shaped. • Being seriously overweight increases risk of diseases. • Being too underweight can result in health problems. • Athletes generally have lower % fat than general population.

  41. Standards for Evaluating Percent Fatfor Men Age < 30 30-39 40-49 >49 High > 28% > 29% > 30% > 31% Optimal 11-21% 12-22% 13-23% 14-24% Very Low  5%  6%  7%  8%

  42. Standards for Evaluating Percent Fatfor Women Age < 30 30-39 40-49 >49 High > 32% > 33% > 34% > 35% Optimal 15-25% 16-26% 17-27% 18-28% Very Low  11%  12%  13%  14%

  43. Weight-reduction Goals • Can determine sound weight reduction goals if know percent fat and body weight. • Based on calculation of fat weight and fat-free weight, healthy weight is determined. • Weight-reduction goal is determined from estimated body weight for the healthy percent body fat.

  44. Healthy Weight • Estimate percent fat. • Fat weight = weight * (%fat  100) • Fat-free weight = weight – fat weight • Healthy weight = fat-free weight  [1 – (Desired %fat  100)]

  45. Screening Tool for Steroid Abuse - FFMI • Fat-free Mass Index (FFMI) • FFMI = fat-free mass/(height)2 • Fat-free mass is in kg • Height is in meters • Normalized FFMI = FFMI + [6.3 x (1.8 – height in meters) • A normalized FFMI > 25 is likely to indicate steroid abuse

  46. Skinfold Assessments of Percent fat of Children and Youth Boys: %fat = [0.735 * (Triceps + Calf)] + 1.0 Girls: %fat = [0.610 * (Triceps + Calf)] + 5.0

  47. Comparison of Body Composition Methods • Most accurate methods are DXA and laboratory assessed body density (Bod Pod and underwater weighing). • Skinfolds is recommended option for field testing: • Accurate and reproducible. • Simple and inexpensive. • Educational

  48. Formative Evaluation ofChapter Objectives • Identify the public health problems associated with body composition. • Identify the methods used to measure body composition of youth and adults. • Identify the limitations of the two-component model for computing percent body fat when applied to children, older adults, and members of various racial groups. • Calculate percent body fat of youths and adults from skinfold equations. • Be able to evaluate body composition of youth and adults. • Calculate weight goals for selected levels of desired percent body fat. • Evaluate the accuracy of the various methods used to measure body composition.

  49. Chapter 12 Evaluating Body Composition

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