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)