Lecture 3: Principles of Energy Expenditure Flashcards
What are the 3 main systems of energy expenditure?
- BEE
- TEF
- EEPA
What minor factors effect TEE?
- cold adaptation
- medications
- emotion
Referred to as adaptive thermogenesis
What needs to be controlled for the get accurate measurements of TEE when comparing 2 people?
The external environment
What are the approximate % for BEE, TEF and EEPA of TEE?
- BEE ~ 60%
- TEF ~ 5-15%
- EEPA varies and can change the BEE
What is included in EEPA?
- EAT
- NEAT
EAT is sum of physical fitness and NEAT is everday living activities
How can REE be measured?
- Direct: Measures changes in body temperature (heat production)
- Indirect: Oxygen consumption as a marker of heat production
What is the premise for indirect measurement of RMR (BEE)?
This is the energy the body needs at complete rest to support itself, therefore the necessary energy is basically from aeorbic processes (respiration) which use oxidative substrates for heat production. O2 is used to break down food during cellular respiration whilst water, CO2 and ATP are produced.
Measures RQ = CO2 produced/ O2 consumed
How many kcal are in a litre of O2?
avg 4.83 kcal energy
+/- 8% regardless of nutrient;
What does indirect calorimetry calculate?
Calculates the energy yield per mole of O2 used = heat production from amount of O2 consumed
Oxygen used per gram of macronutrient metabolized
What are the RQ values for the macronutrients?
- Glucose: 6CO2/6O2 = 1
- TAGs: 16CO2/23O2 = 0.7
- Protein: 5CO2/6O2 = 0.83
Less CO2 is produced for the O2 consumed in fats (and proteins)
Why is the RQ for for fats and proteins lower than for CHO?
A portion of the O2 metabolized with protein and fats is rewuired to combine with the excess hydrogen atoms present in their molecules so less CO2 is formed in relation to the oxygen used.
What is the indirect measure of doubly labelled water?
Water is ingested with 2 labelled isotopes
* deuterium 2H2: stays with water & leaves body
* oxygen-18 18O: shared between water and CO2 and leaves body as both
As it is excreted the isotopes get lower and lower and rate of dissapearance between the unlabelled water and the labelled CO2
Difference in the dissapearance rate between the 2 isotopes + total water pool = unlabelled CO2 production from oxidized fuel
O2 consumption calculated based on RQ from diet and measuring body fluid
What factors influence BEE?
- > 80% variance in BEE is due to fat free mass (body size)
- Some evidence RMR genetically determined
- RMR can vary with menstrual cycle ~10% (higher during luteal stage with increase in estrogen and progesterone)
- Food restriction results in decreased BMR
What factors influence TEF?
- lean body mass = good correlation
- weight loss = variable
- Lower TEF in obesity (controversial)
- prior food intake seems to have greater influence than prior exercise (both under and over eating affect TEF)
- Other: age, athletes, genetics, intestinal FAs
Factors less clear for TEF
What can variance in TEE of people of the same size be accounted to?
Changes in EEPA (mostly NEAT)
Assuming similar EAT
What are the two types of environmental factors?
- egocentric: person is focus
- geocentric: external environment
Interpretation
Energy intake is roughly the same but sales for these technological advancements have increased hence people are moving less and there has been an increase in adipose tissue storage (even though intake hasnt changed much)
