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Chapter 8

Chapter 8. Body Composition, Energy Expenditure, & Energy Balance. Body Weight: What Should We Weigh?. Body mass index BMI = weight (kg)/height (m) 2 Underweight = <18.5 kg/m 2 Healthy = 18.5-24.9 kg/m 2 Overweight = 25-29.9 kg/m 2 Obese class I = 30-34.9 kg/m 2

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Chapter 8

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  1. Chapter 8 Body Composition, Energy Expenditure, & Energy Balance 2009 Cengage-Wadsworth

  2. Body Weight: What Should We Weigh? • Body mass index • BMI = weight (kg)/height (m)2 • Underweight = <18.5 kg/m2 • Healthy = 18.5-24.9 kg/m2 • Overweight = 25-29.9 kg/m2 • Obese class I = 30-34.9 kg/m2 • Obese class II = 35-39.9 kg/m2 • Obese class III = 40 kg/m2 2009 Cengage-Wadsworth

  3. Body Weight: What Should We Weigh? • Formulas • IBW men = 50 kg + 2.3 kg/in >5 ft • IBW women = 45 kg + 2.3 kg/in >5 ft • Frame index 2 value = (elbow breadth/height) x 100 • %IBW = (actual weight/ideal weight) x 100 • IBW = -133.99 + 3.86(height) + 9.52(frame) + 3.08(sex) • Height in in; frame = 1 for small, 2 for medium & 3 for large; sex = +1 for male, -1 for female 2009 Cengage-Wadsworth

  4. The Composition of the Human Body • Reference man • 3% essential fat, 12% storage fat, 44.8% muscle, 14.9% bone, 25.3% other components • Reference woman • 12% essential fat, 15% storage fat, 36% muscle, 12% bone, 25% other components 2009 Cengage-Wadsworth

  5. Methods for Measuring Body Composition • Anthropometry • Skin folds measured & evaluated • Densitometry/hydrodensitometry • Subject weighed underwater, & equations used to estimate bone density & ratio of lean to fat mass • Air-displacement plethysmography • Method to determine body volume 2009 Cengage-Wadsworth

  6. Methods for Measuring Body Composition • Absorptiometry • Single-photon absorptiometry • Dual energy X-ray absorptiometry • Computerized (axial) tomography (CAT or CT) • Creates visual images of cross-sections of the body • Magnetic resonance imaging (MRI) 2009 Cengage-Wadsworth

  7. Methods for Measuring Body Composition • Total body electrical conductivity (TOBEC) • Bioelectrical impedance analysis (BIA) • Ultrasonography or ultrasound • Ifrared interactance • Total body water (TBW) 2009 Cengage-Wadsworth

  8. Methods for Measuring Body Composition • Total body potassium (TBK) • Neutron activation analysis • Overview of methods • Table 8.2 2009 Cengage-Wadsworth

  9. Energy Balance • Energy balance - energy intake = energy output • Imbalance - weight gain or loss • Prevalence of obesity • Overweight/obese: 70% of men, 61% of women • >33% of children overweight/obese 2009 Cengage-Wadsworth

  10. Components of Energy Expenditure • Basal metabolic rate & resting energy expenditure • Expenditure for respiration, heartbeat, renal function, blood circulation • Measured in person in postabsorptive state, supine, motionless, thermoneutral environment (BEE) 2009 Cengage-Wadsworth

  11. Components of Energy Expenditure • Thermic effect of food • Protein increases expenditure 20%-30% • CHO: 5%-10% • Fat: 0%-5% • Energy expenditure of physical activity • Thermoregulation • Alterations in metabolism that occur as the body maintains its internal temperature 2009 Cengage-Wadsworth

  12. Assessing Energy Expenditure • Direct calorimetry • Measures dissipation of heat from the body • Indirect calorimetry • Measures consumption of O2 & expiration of CO2 • The respiratory quotient & substrate oxidation • The respiratory quotient & energy expenditure 2009 Cengage-Wadsworth

  13. Assessing Energy Expenditure • Doubly labeled water • Stable isotopes of water given as H218O & 2H2O • Disappearance of H218O & 2H2O measured in blood & urine for ~3 weeks 2009 Cengage-Wadsworth

  14. Assessing Energy Expenditure • Derived formulas • Harris-Benedict • Men: BMR = 66.5 + (13.7 x W) + (5.0 x H) - (6.8 x A) • Women: BMR = 655.1 + (9.56 x W) + (1.85 x H) - (4.7 x A) • Mifflin-St. Jeor • Men: REE = (10 x W) + (6.25 x H) - (5 x A) + 5 • Women: REE = (10 x W) + 6.25 x H) - (5 x A) - 161 2009 Cengage-Wadsworth

  15. Assessing Energy Expenditure • Food & Nutrition Board • Men: EER = 662 - (9.53 x age) + PA(15.91 x weight + 539.6 x height) • Women: EER = 354 - (6.91 x age) + PA(9.36 x weight + 726 x height) 2009 Cengage-Wadsworth

  16. Regulation of Body Weight & Composition • Genetic influences • Melanocortin receptor • Uncoupling proteins • Hypothesis that people have genetically predetermined weights • Hormonal influences • Ghrelin • Arcuate nucleus in hypothalamus • Cholecystokinin • Leptin • Insulin 2009 Cengage-Wadsworth

  17. Regulation of Body Weight & Composition • Positive energy balance • Energy provided by alcohol, CHO, & fat (in that order) • CHO used for FA synthesis when it exceeds total energy needs • FAs not used for energy are stored • Continued imbalance - enlarged adipocytes; eventially more produced 2009 Cengage-Wadsworth

  18. Regulation of Body Weight & Composition • Negative energy balance • Required to lose body fat • Calorie restriction results in weight loss • Research on energy-nutrient distribution in weight-loss diets 2009 Cengage-Wadsworth

  19. Perspective 8 Eating Disorders 2009 Cengage-Wadsworth

  20. Eating Disorders • Anorexia nervosa • Bulimia nervosa • Binge eating disorder • Disordered eating • The female athlete triad 2009 Cengage-Wadsworth

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