What is a bomb calorimeter used to measure?
- measures the total energy value of food
- This is known as the `heat of combustion
- The increase in water temperature directly reflects the heat released during a food’s oxidation
What is heat of combustion
- macronutrients that have undergone complete oxidation
WHy do lipids release more energy
- becaause CHO of a hydrogen to oxygen ratio of 2:1, but lipds ratio are much larger than that meaning they have more hydrogen atoms to be cleaved and oxidized releasing more energy
lists the average HOC values for each macronutrient in kilocalories per gram (kcal/g):
4 kcal/g for CHO
9 kcal/g for lipds
5 kcal/g for proteins
what is net energy value
- energy that is available to the body and can be used
What is the key difference between the Heat of Combustion (HOC) and the Net Energy Value of protein, and why does this difference exist?
- heat of combustion is the gross energy value of food while the net energy value is the energy available to the body to be used
- the different exist because the body can’t fully oxidize protein because nitrogen combines with water to form which is an excreted from the body this causes a reduction in total chemical energy from protein
- for carbohydrates and protein the heat of combustion is equal to the net energy value because the body can fully oxidize them
what is the difference between direct and indirect calorimetry?
- indirect calorimetry measures oxygen uptake and CO2 production because oxygen uptake is proportional to the amount of heat produced
- direct calorimetry measures total energy expenditure, however it can measure heat that is not related to the metabolic process such as fans or lightbulbs
What one method to measure energy expenditure using direct calorimeter
- human calorimeter
- an airtitght chamber that a person can live in
- the changes in water temperature directly relate to an indiviauls energy metabolism
Name some methods of indirect calorimetry
- closed circuit spirametry
- open circuit spirametry
- portable spirometry
bag technique - double-labelled water technique
Describe a closed circuit
- subject breathes 100% of oxygen pre-filled container
- CO2 is absorbed in exhaled air and volume of O2 uptake is measured
Describe and open circuit
- subject inhale ambient air (79% nitrogen, 20% oxygen, 0.03% CO2)
- this indirectly measures ongoing process of energy metabolism
What is a portable spirometry
- ambient air passes through a two-way valve
- expired air travels through a gas meter to measure total expired air
- good for real life activities
What is the douglas bag technique
- ambient air is brather through one side of a valve and exhales though the other side of the valve into the douglas bag
Name the advantages and disadvantages of doubles lebeled water technique
- used with volunteers outside of lab to give ‘free living’ EE because EE rates are higher in lab.
- no equipment attached
- easy to sample body fluids, saliva, urine or blood
- disadvantage: measures CO2 production but estimates VO2 and very expensive
what is the equation for respiratory exhange rate?
- CO2 consumed / O2 consumes
What does RG provide
- it provides information on what nutrient mixture was catabolized for energy
What are RQ values for CHO, fat and protein
- CHO: 1
- Fat: 0.7
- protein: 0.82
What does an RER value greater than 1.00 indicate, and why does this happen?
- it means that person is performing an exhaustive exercise and is over breathing. - This happens during intense exercise when the bodys energy demand exceeds what aerobic metabolism can provide, leading to an increase in anaerobic metabolism. this process produces lot of lactate
- to prevent blood from become very acidic sodium bicarbonate will act as a buffer and this buffering process produces an increase in CO2
What does an RER value less than 0.7 indicate? Why does this happen?
- after exhaustive exercise with glucose depletion
- This happens because of depletion in bicarbonate due to buffering lactate. To replenish these stores the body retains CO2 in its cells and fluids
what are the 3 factors that determine total daily expenditure
- basal metabolic rate: calories needed to do basic physiological function
- thermic effect of feeding: energy it takes to digest, absorb, transport nutrients etc
- thermic effect of physical activity: the energy expended on physical activity
What is a MET
- it represents resting oxygen consumption or energy expenditure
- 1 MET = 3.5 O2 /kg min
