WEEK 4 Energy expenditure and physical activity Flashcards
What is direct vs indirect calorimetry?
Measuring energy expenditure based on heat release = direct calorimetry, to distinguish it from measurements based on gas exchange = indirect calorimetry.
What is the procedure of DLW and what is measured?
- Stable isotopes (2H2O: deuterium and Oxygen-18: 18O) are ingested as water.
- Distributed in the body water pool
3a. Deuterium = eliminated as water
3b. Oxygen isotope = eliminated as water + CO2
Difference in elimination rate = CO2 production over the measurement time.
Formula for energy expenditure?
Food + O2 -> H2O + CO2 + energy (heat+work)
What is the principle of direct calorimetry?
If external work = 0, the heat energy delivered from the chamber = equal to metabolic rate.
Very accurate, but not convenient at all
What is the principle of indirect calorimetry? What is it dependent on?
Released energy from substrates is related to O2 consumption (VO2) and CO2 production (VO2). Computes heat from gaseous exchange
(However, depends on the substrate. Meal/diet = mix different substrates)
What are two disadv. of calorimetry?
- Specialized (expensive) equipment
- Only applicable in lab settings, limited in free-living conditions
DLW: when are the two samples collected? ‘formula’ of elimination and production?
Collect two measurement: initial sample (equilibrium) and between 4 - 24 days
18O elimination (water+CO2) - 2H2 elimination (water) = CO2 production (VCO2)
Pro’s of DLW?
- Considered golden standard
- Validity has been established in respiration chamber
- Free living
- Measurement error <5%
Cons of DLW?
- High cost, specialized equipment, labour intensive
- TEE over 4-21 days: no information other components (PA)
- small sample size
Assumptions for DLW?
> Total body water remains constant (no weight loss)
> No isotopic exchange with non-aqueous body tissue (correct for that) and fractionation (correction factors)
> RER (RQ) 0> 0.85 on mixed diet
(respiratory quotient)
What is something to take into mind with heart rate monitoring?
> Low heart rate correlation to EE with low exercise (also, stress, caffeine, ill etc)
T(D)EE =?
Total (daily) energy expenditure
What are the 3 components of TEE? %?
- BMR (basal metabolic rate) ~60-70%
- DIT (Diet-induced thermogenesis) ~10%
- PA (Physical activity) ~20-30%
BMR = not the same as resting (RMR) or sleeping (SMR) metabolic rate. What is it dependent on?
- Body weight and body composition
- Age & sex
- Various (climate, life cycle, external factors)
BMR = not the same as resting (RMR) or sleeping (SMR) metabolic rate. What is it dependent on?
- Body weight and body composition
- Age & sex
- Various (climate, life cycle, external factors)
What does DIT depend on?
- size of meal
- composition of meal
- texture of meal
- non-nutrient substances
Physical activity can be measured in MET scores. 1 MET = ?
1 MET = basal (resting) metabolic state
PAL = ? formula?
Physical activity level. PAL = TEE/BMR
Difference MET and PAL?
MET is more for specific excercises, PAL more general for daily activity
What is the cutoff of METs for PA do be sedentary?
MET < 1,5
Categorize PAL values from bed rest to very high activity level
< 1.2 = Bed rested
1.2 - 1.55 = Low activity level: sedentary
1.55 - 1.71 = Medium activity level, office work
1.71 - 1.95 = high activity level, manual work and exercise
> 1.95 = Very high activity level: Fair amount of manual work or exercise training
What is the formula of PAL?
PAL = TEE/RMR(or BMR)
What is the formula of TEE?
TEE = PAEE + RMR(or BMR) + DIT
What is the formula of DIT?
DIT = 10% of TEE
What is the most variable part of TEE?
PA level
What are the 4 methods to assess PA/EE?
- Indirect calorimetry & doubly labelled water
- Self reported methods
- Questionnaire
- Logs/diaries
- Heart rate monitor
- Motion sensors
- Pedometer
- Accelerometers
Cons of indirect calorimetry?
Costly, labour intensive, specialized equipment
Restricted to small sample size
Non-free living
Pros of self-reported methods?
- Low costs
- Large population
- Costumisable (choose time frame/specific exercise)
- Easy
Cons self-reported measures?
- Poor correlation with EE (DLW)
- (only) ranking of subjects
- Socially desirable answers
- Interference with activities (diary)
- Miscoding, misreporting..
Pros heart rate monitor?
Close relationship exercise
Individual calibration curve
Relatively cheap
Information intensity/frequency/duration activity
Cons heart rate monitor?
HR affected by other factors (stress, ilness, drugs)
Agreement with DLW poor -> particular in the range of low intensity PA
What motion sensors are there?
Pedometer, accelerometer
What does the pedometer do? Adv/disadv?
Count steps
Pros
Small/cheap
Cons
Lack sensitivity
Very limited utility estimating EE
What does the accelerometer do? Adv, disadv?
Measure acceleration
Adv
Measures amount & intensity
Small, cheap
Disadv
Not all activity (cycling, upper body etc)
Estimatin EE = poor - promising
