Understanding Body Composition for Better Health

1. Body Composition

2. Body Composition 2 component model Fat tissue Fat free tissue

3. Body Composition Why the interest? Excess body fat • Hypertension • Type 2 diabetes • Hyperlipidemia • Certain cancers • Poor performance/function • Poor self-image Incident of overweight is ↑ng Want to “look good”

4. Body Composition Terminology Depot or storage fat – fat stored in adipose cells as nutritional reserve Essential fats – fats necessary for normal physiologic function

5. Body Composition Terminology Lean body mass (wt) – body mass minus depot fat Fat free mass (wt) – body mass minus all fat (depot & essential)

6. Body Composition Relative %age of body weight that is fat & fat-free tissue Lab & field tests vary in complexity, expense

7. Anthropometry Measurement of the human body

8. Anthropometry Ht/wt Circumference/girths Skinfolds Hydrostatic weighing Bioelectrical impedance DXA TOBEC X-ray

9. Body Composition - %Fat Norms Classification Women Men

10. Body Composition - Tests • Densitometry • Two component model • Fat & fat free mass • Ratio of body mass to body volume (DB=BW/BV) • Body mass determined form body weight • Body volume from under water weighing or plethysmography

11. Densitometry • Hydrostatic (under water) weighing • Criterion, gold standard

12. Densitometry • Hydrostatic (under water) weighing • Archimedes’ principle – when a body is immersed in water, it is buoyed by a counterforce equal to the weight of the water displaced • The loss of weight in water, corrected for density of the water, allows calculation of body volume

15. Densitometry • RV • Density of H2O • Trapped gas in GI tract (100 ml) • Body weight (dry) • Body weight (wet)

16. Body Composition - Densitometry Body density = weight in air (weight in air – weight in water) – Residual Density of the water volume

17. Body Composition - Densitometry Body density = bone & muscle more dense than water, fat tissue less dense

18. Body Composition - Densitometry Plethysmography • air displacement – Δs in pressure in a closed chamber

19. Bodpod

20. Body Composition - Densitometry %fat = 457 - 414.2 Body Density %fat = 495 - 450 Body Density

21. Body Composition – Anthropometric Methods • Height • Weight • Circumferences • Skinfolds

22. Body Composition – Anthropometric Methods • Reliability & validity • Skill of the measurer • Type of caliper or tape measure • Subject factors related to skinfold compressibility, edema, & variability in fat pattern & distribution • Prediction equation used to estimate fatness

23. Body Composition – Anthropometric Methods • Body Mass Index (BMI) • Assess weight relative to height • [body weight (kg)/height (m2)] • BMI > 25 – increased health risk • 25.0 to 29.9 = Overweight • > 30 = Obese • See Table 4-1 pg.58 & Table 4-2 pg.59

24. Body Composition – Anthropometric Methods • Waist-to-hip circumference • Body fat distribution • More fat on trunk (abdominal fat) = greater risk of HTN, type 2 diabetes, hyperlipidemia, CAD, premature death • Health risk is high • W/H ratio > 0.94 in young men • W/H ratio > 0.82 in young women • W/H ratio > 1.03 in men 60-69 yrs • W/H ratio > 0.90 in women 60-69 yrs See Box 4-1 & Table 4-3 pgs.60-61 ACSM GET&P

25. Classification of Disease Risk Based on Body mass Index (BMI) and Waist Circumference (Table4-1) Disease Risk Relative to normal Weight and Waist Circumference

26. Body Composition – Anthropometric Methods • Skinfolds • Amount of subcutaneous fat is proportional to total body fat

27. Box 4-2. Standardized Description of Skinfold Sites & Procedures Continued • Procedures • All measurements on the right side of the body • Caliper should be placed 1 cm away from the thumb & finger, perpendicular to the skinfold, & halfway b/n the crest & the base of the fold

28. Box 4-2. Standardized Description of Skinfold Sites and Procedures Continued • Pinch should be maintained while reading the caliper • Wait 1 to 2 s (& not longer) before reading caliper • Take duplicate measures at each site & retest if duplicate measurements are not w/n 1 to 2 mm • Rotate through measurement sites or allow time for skin to regain normal texture & thickness

29. Box 4-2. Standardized Description of Skinfold Sites & Procedures • Skinfold Site • Abdominal Vertical fold; 2cm to the right side of the umbilicus • Triceps Vertical fold; on the posterior midline of the upper arm, halfway between the acromion & the olecranon processes, w/ the arm held freely to the side of the body • Biceps Vertical fold; on the anterior aspect of the arm over the belly of the biceps muscle, 1 cm above the level used to mark the triceps site

30. Box 4-2. Standardized Description of Skinfold Sites & Procedures Continued • Skinfold Site Continued • Chest/Pectoral Diagonal fold; one-half the distance between the anterior axillary line & the nipple (men) or one-third the distance b/n the anterior axillary line & the nipple (women) • Medial Calf Vertical fold; at the maximum circumference of the calf on the midline of its medial border

31. Box 4-2. Standardized Description of Skinfold Sites & Procedures Continued • Skinfold Site Continued • Midaxillary Vertical fold; on the midaxillary line at the level of the xiphoid process of the sternum (An alternate method is a horizontal fold taken at the level of the xiphoid/sternal in the midaxillary line • Subscapular Diagonal fold (at a 45 angle); 1 to 2 cm below the inferior angle of the scapula

32. Box 4-2. Standardized Description of Skinfold Sites & Procedures Continued • Suprailiac Diagonal fold; in line w/ the natural angle of the iliac crest taken in the anterior axillary line immediately superior to the iliac crest • Thigh Vertical fold; on the anterior midline of the thigh, midway b/ the proximal border of the patella & the inguinal crease (hip)

33. Table 4-5. Body Composition (%Body Fat) For Men*

34. Table 4-6. Body Composition (%Body Fat) For Women*

35. Body Composition – Other Techniques • Bioelectrical Impedance Analysis (BIA) • Volume of FFM is proportional to the electrical conductivity of the body • Small electrical current is passed through body • Measures resistance to current • Fat is poor conductor – 14 to 22% water • Lean tissue is good conductor - >90% water • Assumes normal hydration

36. Body Composition – Other Techniques • Bioelectrical Impedance Analysis (BIA) • Does not require a high degree of technical skill • More comfortable • Requires minimal cooperation • Intrudes less on privacy

37. Body Composition – Other Techniques • Dual Energy X-ray Absorptiometry (DEXA) • Assess total bone mineral, bone, fat, & lean tissues • Uses three component model (fat, solids, water) • Near-infrared interactance (NIR) • Light absorption & reflection • Chemical composition of the body • Accuracy 4 to 11%

38. Dual X-Ray Absorptiometry

39. Prediction Equations • Population specific • Derived on homogeneous population • General equations • Diverse, heterogeneous samples that account for differences in age, sex, race, ethnicity, etc.

40. Prediction Equations • Equation Selection • To whom is the equation applicable • Was equation developed on an appropriate reference model? • Was a representative sample studied? • How were predictor variables measured? • Was the equation cross-validated? • Does equation give accurate estimates? (2.5 to 3.5% - %fat) (2.5 to 3.5 kg – FFM)