MEDI211 Lecture Notes - Lecture 2: Calorimeter, Antoine Lavoisier, Basal Metabolic Rate
Week 1 Lecture 2 – Concepts of energy balance
Lecture Objectives:
1. To introduce students to concepts of energy balance: intake, expenditure and storage.
2. Demonstrate an understanding of the physiological principles underlying metabolic
rates.
•Energy metabolism encompasses all the chemical reactions by which the body obtains and
spends energy from nutrients.
•Anabolic processes build substances; catabolic processes breakdown substances. Metabolism
is made up of oxidation and reduction reactions.
•Oxidation must be tightly controlled in biological systems to avoid dangerous rates of heat
production, as oxidation in metabolism results in ATP formation - energy expenditure.
•Metabolic coupling: one metabolic reaction cannot proceed without the reaction it is linked to
- anabolic and catabolic pathways are linked.
Energy balance :
1st Law of Thermodynamics - energy cannot be created or destroyed - in a closed system
energy is constant. For a steady state, energy intake = energy expenditure.
Energy intake: (1kcal = 4.2kJ)
1g carbohydrate = 4kcal = 17kJ
1g fat = 9kcal = 38kJ
1g protein = 4kcal = 17kJ
Fat (adipose tissue) is able to sustain our resting metabolic rate for much longer per g than
carbohydrates.
Protein is really only used for energy during starvation, when it can provide ~15% of our
resting metabolic rate.
Calorimetry: the science of measuring heat production.
•Direct calorimetry: heat provides a measure of food energy composition as kcalories - the
amount of heat released is equivalent to the amount of energy.
•Indirect calorimetry: measures O2 consumption and CO2 production as an indicator of heat
production; O2 consumption is directly proportional to heat production so indicates energy
expenditure.
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Document Summary
To introduce students to concepts of energy balance: intake, expenditure and storage. Demonstrate an understanding of the physiological principles underlying metabolic rates. Energy metabolism encompasses all the chemical reactions by which the body obtains and spends energy from nutrients. Anabolic processes build substances; catabolic processes breakdown substances. Metabolism is made up of oxidation and reduction reactions. Oxidation must be tightly controlled in biological systems to avoid dangerous rates of heat production, as oxidation in metabolism results in atp formation - energy expenditure. Metabolic coupling: one metabolic reaction cannot proceed without the reaction it is linked to. 1st law of thermodynamics - energy cannot be created or destroyed - in a closed system energy is constant. For a steady state, energy intake = energy expenditure. Fat (adipose tissue) is able to sustain our resting metabolic rate for much longer per g than carbohydrates.
