Measurement of Energy in Food and During Physical Activity
Chapter 6
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.
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
Units of Energy
Temperature reflects a quantitative measure of an object’s hotness or coldness.
Heat describes energy transfer from one body or system to another.
Temperature Versus Heat
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
Bomb Calorimeter
Bomb Calorimeter
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
Heat of Combustion
Atwater – chemist Actual energy available to the body Coefficient of digestibility • Affected by dietary fiber• Atwater general factors
Carbohydrates: 4 Lipids: 9 Proteins: 4
Net Energy Value
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.
Direct Calorimetry
Direct Calorimetry
Energy expenditure Measurements of oxygen uptake and carbon
dioxide production using:• Closed-circuit spirometry• Open-circuit spirometry
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
Indirect Calorimetry
Closed or Open Circuit Spirometry
Portable Spirometry
Bag technique
Computerized Instrumentation
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
Respiratory Quotient (RQ)
RQ equals 1.00 for carbohydrate, 0.70 for fat, 0.82 for mixed diet
Respiratory Quotient (RQ)
Carbohydrate◦ C6H12O6 + 6 O2 → 6 H2O + 6 CO2
◦ RQ = 6 CO2 / 6 O2 ◦ RQ = 1.00
Respiratory Quotient (RQ)
Lipid◦ C16H32O2 + 23 O2 + 6 H2O → 16 H2O + 16 CO2
◦ RQ = 16 CO2 / 16 H2O ◦ RQ = .696 (.70)
Respiratory Quotient (RQ)
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
Respiratory Exchange Ratio (RER)
R above 1.00• Hyperventilation due to acidosis • Exhaustive exercise
Lactic acid HLA + NaHCO3 → NaLa + H2CO3 → H2O + CO2
Respiratory Exchange Ratio (RER)
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
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
Total Daily Energy Expenditure
Energy expended during physical activity and recovery • Physical activity
Accounts for between 15% and 30% total daily energy expenditure (TDEE)
Total Daily Energy Expenditure
Thermogenic influence of food consumed • Dietary-induced thermogenesis
Can influence metabolic rate substantially Energy of digestion
Total Daily Energy Expenditure
Climate• Tropical
5-20% higher RMR• Hot environment
Additional metabolic load• Cooling body
Total Daily Energy Expenditure
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 =
The Metabolic Equivalent (MET)