Measurement of Energy in Food and During Physical Activity

1. Measurement of Energy in Food and During Physical Activity Chapter 6

2. Units of Energy • Calorie • One calorie expresses the quantity of heat necessary to raise the temperature of 1 g of water by 1° Celsius. • Kilocalorie (kCal) • One calorie expresses the quantity of heat necessary to raise the temperature of 1 kg (1 L) of water by 1° Celsius.

3. Units of Energy • Joule or Kilojoule • Standard international unit expressing energy • 1 cal = 4.186 J • 1 kCal = 1000 cal = 4186 J = 4.184 kJ • Megajoule • 1000 kJ

4. Temperature Versus Heat • Temperature reflects a quantitative measure of an object’s hotness or coldness. • Heat describes energy transfer from one body or system to another.

5. Bomb Calorimeter • Measures total energy value of foods • Type of calorimetry • Direct • Measures heat liberated as food burns • Sealed chamber • Oxygen, under pressure • Surrounded by water jacket • Increase in water temperature directly reflects the heat released during a food’s oxidation. • Heat of combustion

6. Bomb Calorimeter

7. Heat of Combustion • Carbohydrates • Glucose = 3.74 kCal/g • Glycogen = 4.19 kCal/g • Average = 4.2 kCal/g • Lipids • Beef, pork fat = 9.5 kCal/g • Butterfat = 9.27 kCal/g • Average = 9.4 kCal • Proteins • Beans = 5.75 kCal/g • Average = 5.65 kCal

8. Net Energy Value • Atwater – chemist • Actual energy available to the body • Coefficient of digestibility • Affected by dietary fiber • Atwater general factors • Carbohydrates: 4 • Lipids: 9 • Proteins: 4

9. Direct Calorimetry • Directly measures energy expenditure • Human calorimeter • Airtight chamber • A person lives or works in the chamber for an extended period of time. • Changes in water temperature relate directly to an individual’s energy metabolism.

10. Direct Calorimetry

11. Indirect Calorimetry • Energy expenditure • Measurements of oxygen uptake and carbon dioxide production using: • Closed-circuit spirometry • Open-circuit spirometry

12. Indirect Calorimetry • Closed-circuit • Subject breathes 100% oxygen from a prefilled container. • A canister of soda lime absorbs the carbon dioxide in exhaled air. • Open-circuit • Subject inhales ambient air • Indirectly reflects energy metabolism

13. Closed or Open Circuit Spirometry

14. Portable Spirometry

15. Bag technique

16. Computerized Instrumentation

17. Respiratory Quotient (RQ) • The ratio of carbon dioxide produced to oxygen consumed • Measured at the exercising muscle • Reflects cellular respiration • Rest and Steady state • The RQ provides information about the nutrient mixture catabolized for energy. • Carbohydrate • Fat

18. Respiratory Quotient (RQ) • RQ equals • 1.00 for carbohydrate, • 0.70 for fat, • 0.82 for mixed diet

19. Respiratory Quotient (RQ) • Carbohydrate • C6H12O6 + 6 O2 → 6 H2O + 6 CO2 • RQ = 6 CO2 / 6 O2 • RQ = 1.00

20. Respiratory Quotient (RQ) • Lipid • C16H32O2 + 23 O2 + 6 H2O → 16 H2O + 16 CO2 • RQ = 16 CO2 / 16 H2O • RQ = .696 (.70)

21. Respiratory Exchange Ratio (RER) • Ratio of carbon dioxide produced to oxygen consumed • Measured at the mouth (expired gases) • Computed in exactly the same manner as RQ • VCO2/VO2 • Not as effective in determining substrate use as some CO2 from buffering lactic acid (Non-metabolic CO2 production) can raise RER

22. Respiratory Exchange Ratio (RER) • R above 1.00 • Hyperventilation due to acidosis • Exhaustive exercise • Lactic acid • HLA + NaHCO3→NaLa + H2CO3→ H2O + CO2

23. Total Daily Energy Expenditure • Factors that determine total daily energy expenditure (TDEE): • Basal metabolic rate – minimum energy requirement to sustain cellular respiration • Decreases with age • Slower decline with exercise • Lower in females than males

24. Total Daily Energy Expenditure • BMR measurement (metabolic cart) • No food or exertion – 12 h • Following 30-60 min quiet rest • Resting metabolic rate • Awake, moving around

25. Total Daily Energy Expenditure • Energy expended during physical activity and recovery • Physical activity • Accounts for between 15% and 30% total daily energy expenditure (TDEE)

26. Total Daily Energy Expenditure • Thermogenic influence of food consumed • Dietary-induced thermogenesis • Can influence metabolic rate substantially • Energy of digestion

27. Total Daily Energy Expenditure • Climate • Tropical • 5-20% higher RMR • Hot environment • Additional metabolic load • Cooling body

28. The Metabolic Equivalent (MET) • One MET represents an adult’s average seated, resting oxygen consumption or energy expenditure. • Convenient way to rate exercise intensity • 1 MET = 3.5 mL/kg/min • 1 MET represents an energy expenditure of ~1.2 kcal/min for 70 kg person • 5 METs =