Lecture 4-Energy Metabolism

Question 1

Energy Terminology:

Answer 1

• Calorie (cal) is a measure of heat
• Kcal= 1000 calories = 1 Calorie = 1 Cal
1 kcal= 4.18 kJ (energy required to raise the temperature of 1 kg (1 L) of water by 1 degree C

Question 2

Positive Energy Balance:

Answer 2

• Weight gain
• Infertility
• Increased blood lipids
Insulin resistance

Question 3

Negative Energy Balance:

Answer 3

• Weight loss
• Infection
• Loss of performance
Reduced bone mass

Question 4

Estimating Energy in Foods:

Answer 4

• Calorimetry- measurement of heat production

Use heat as an indicator of the amount of energy is stored in chemical bonds of foods (C-H bonds)

Question 5

Bomb Calorimetry:

Answer 5

• Dry and weigh sample (~1g) and place in enclosed chamber (the bomb) with oxygen
• Sample is ignited
• Heat released is absorbed by water and measured
• Heat of energy (gross energy= maximum energy)
• Overestimates energy (we don’t digest food like a bomb calorimeter)
○ i.e. fibre- provides no energy in us because we can’t digest it, but in a bomb calorimeter it will still burn and release energy
Doesn’t take into account the energy needed for digestion and absorption

Question 6

Atwater Values/Physiological Fuel Values:

Answer 6

Chart

Question 7

Energy From Fat vs. Carbohydrates vs. Protein:

Answer 7

• CHO has a hydrogen to oxygen ratio of 2:1
• Protein has nitrogen, which contributes to gross energy, but our bodies don’t use nitrogen for energy (it is passed through body via urine)
• Lipids have a very high ratio of hydrogen to oxygen
○ Lots of hydrogen atoms available for cleavage and oxidation for energy
Variability in structures, ratio differs depends on the lipid

Example

Question 8

Factors Affecting Combustion of Fatty Acids:

Answer 8

• Chain length
○ Lipids with longer chain lengths release more energy
• Degree of unsaturation
○ Saturated fats (no double bonds) will release more energy
Unsaturated fats have fewer hydrogens, releases less energy

Question 9

Atwater Values and Nutritional Labels:

Answer 9

• Not sure if fibre is taken into account when determining the caloric content (debatable)
○ Can be fermented, gives you energy
Many manufacturers say no, no evidence that say fermentation of fibre is producing energy that is using used by host, or if it is being used for something else (not being used as energy)

Chart

Question 10

Heat Increment of Feeding (HIF):

Answer 10

• Also called the thermic effect of food
• Energy used for digestion, absorption, distribution, and storage of nutrients
• 5-30% of energy usage of the body
• Used to determine Net Energy
○ Leftover energy used to sustain other activities
○ Net Energy= Available Energy- HIF
Net energy supports basal metabolism, physical activity, growth…etc

Question 11

Energy Loss From Food:

Answer 11

Diagram and Explanation

Question 12

Total Energy Expenditure:

Answer 12

• 3 primary components
○ Basal metabolic rate (BMR)
○ Thermic effect of food (HIF)
○ Physical activity energy expenditure (PAEE)
• Thermoregulation
○ Not really factored in because it is easily to thermoregulate without using energy
i.e. cold- put on a sweater

Diagram

Question 13

Basal Metabolic Rate:

Answer 13

• Measured under the following conditions
○ Shortly after waking
○ Post-absorptive state
○ Lying down
○ Completely relaxed
○ Comfortable room temperature
• BMR= kcal/ 24 hours
○ Amount of energy a person needs for 24 hours
Activity of key tissues (muscle and bone primarily)

Question 14

Calculating BMR:

Answer 14

• Based on metabolic weight
	• A= Metabolically active tissue
		○ Constant for different species
		○ Energy used by fat free tissues (muscle and bone)
		○ Typical values
			§ Human=70
			§ Dog=30
			§ Horse=155
	• M= Body weight in kilograms
	• 0.75- Kleiber's Law
		○ Used for all vertebrates, invertebrates, and even unicellular organisms
**Equation and Example**

Question 15

Harris-Benedict Equation:

Answer 15

• Determines BMR, but takes into account individual differences (age, gender, height…etc)

Question 16

Basal Metabolic Rate (BMR) vs. Resting Metabolic Rate (RMR):

Answer 16

• Same thing, but RMR is less strict with criteria when measuring (lying down..etc)
RMR gives you rougher data

Question 17

Factors that Affect BMR:

Answer 17

• Genetics
○ Inheritance of a fast or slow metabolic rate
• Age
○ Younger people have a high metabolic rate due to greater muscle mass
• Sex
○ Men have higher metabolic rate due to greater muscle mass
• Exercise
○ Exercise changes body tissue proportions
○ Muscle has a higher metabolic rate than fat
• Temperature
Maintaining thermoregulation

Diagram

Question 18

Katch-Mcardle BMR Equation:

Answer 18

• Method of measuring BMR by determining body fat composition
Not used often, it is expensive to determine body fat percentage

Question 19

Measuring Total Energy Expenditure:

Answer 19

All metabolic processes in the body generate heat, heat production can be used to measure energy expenditure

Direct, Indirect Calorimetry

Equation

Question 20

Direct Calorimetry

Answer 20

○ Bomb calorimetry
○ Measure the heat a person generates (heat loss from body metabolic processes)
Very expensive, impractical

Question 21

Indirect Calorimetry

Answer 21

○ Energy releasing reactions in the body require the use of oxygen
○ Measures heat production by measuring
§ Oxygen consumption (L)
§ CO2 production (L)
§ Urinary nitrogen loss (g)
○ Cannot account for anaerobic processes (production of lactate from glucose during intense exercise)
§ Energy is produced, but not produced due to oxygen consumption so it is missed
○ Advantages
§ Can be used with animals
§ Can be used in lots of situations
§ Can determine the type of substrate being oxidized
○ Disadvantages
§ Hard to get an airtight seal
§ Masks are impractical
§ Hyperventilation
□ Produces a lot of CO2, but not because of energy usage
Direct and indirect calorimetry provide results with a difference of less than 1%

Question 22

Respiratory Quotient (RQ):

Answer 22

• Provides information about
○ Energy expenditure
○ Biological substrate being oxidized
• Non protein RQ (protein contributes very little to energy metabolism)
Differences in chemical composition means that each macronutrient requires a different amount of oxygen uptake in relation to CO2 produced

• For each non protein RQ value, there is a caloric value for each L of O2 consumed or CO2 produced Also tells you how much CHO and fat contribute to energy

Equation and Example

Question 23

Assumptions For RQ

Answer 23

• Only CHO and fat are metabolized
• No synthesis is taking place as the same time as breakdown
Amount of CO2 exhaled= amount of CO2 produced by tissues

Question 24

Crossover Concept:

Answer 24

• Different types of exercise uses different macronutrients
• Crossover point is when muscle starts to use more CHO than fat to sustain power or more fat than CHO
○ Endurance burns fat, high intensity burns CHO
○ Training moves crossover point to the right, so more fat is used than CHO
• Over time, biochemical adaptations occur
○ If fat was used predominantly in exercise, muscle will adapt so it can break down fat more easily
If CHO was used predominantly, CHO will be broken down more easily

Diagram