Lecture 4-Energy Metabolism Flashcards
Energy Terminology:
• 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
Positive Energy Balance:
• Weight gain
• Infertility
• Increased blood lipids
Insulin resistance
Negative Energy Balance:
• Weight loss
• Infection
• Loss of performance
Reduced bone mass
Estimating Energy in Foods:
• 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)
Bomb Calorimetry:
• 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
Atwater Values/Physiological Fuel Values:
Chart
Energy From Fat vs. Carbohydrates vs. Protein:
• 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
Factors Affecting Combustion of Fatty Acids:
• 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
Atwater Values and Nutritional Labels:
• 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
Heat Increment of Feeding (HIF):
• 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
Energy Loss From Food:
Diagram and Explanation
Total Energy Expenditure:
• 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
Basal Metabolic Rate:
• 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)
Calculating BMR:
• 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**
Harris-Benedict Equation:
• Determines BMR, but takes into account individual differences (age, gender, height…etc)
Basal Metabolic Rate (BMR) vs. Resting Metabolic Rate (RMR):
• Same thing, but RMR is less strict with criteria when measuring (lying down..etc)
RMR gives you rougher data
Factors that Affect BMR:
• 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
Katch-Mcardle BMR Equation:
• Method of measuring BMR by determining body fat composition
Not used often, it is expensive to determine body fat percentage
Measuring Total Energy Expenditure:
All metabolic processes in the body generate heat, heat production can be used to measure energy expenditure
Direct, Indirect Calorimetry
Equation
Direct Calorimetry
○ Bomb calorimetry
○ Measure the heat a person generates (heat loss from body metabolic processes)
Very expensive, impractical
Indirect Calorimetry
○ 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%
Respiratory Quotient (RQ):
• 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
Assumptions For RQ
• 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
Crossover Concept:
• 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
