PEDS334 Lecture Notes - Indirect Calorimetry, Calorimetry, Last Meal

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Published on 21 Nov 2012
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Sept 12 Energy Balance Continued
One of the things that affects the abilty to burn calories is age
Women tend to have a higher % body fat
Resting Metabolic Rate
What is it? the energy needed to sustain basic life function
How is it measured?
Direct Calorimetry – heat production = metabolism
Indirect Calorimetry – where you use the same procedures for VO2, but they
put a bigger mask on the test person
What factors influence RMR? Age, body composition, gender
Indirect Calorimetry
Based on Analysis of expired gases
Determine RER = ?
Ratio of VCO2/VO2
Amount of CO2 produced varies with substrate
RER of 0.7 = Fat
RER of 1.0 = Carbohydrate
Thus measuring VO2 and VCO2 over time can give us an estimate of energy
Other indirect measures include HR, METS
Variability in Measurement
Due to:
1.) Instrument error
2.) Investigator error
3.) Biological variability (mood, stress, rhythms, activity, intake, etc.)
Must be minimized to keep error of measurement as low as possible
Factors Influencing RMR
Fat free mass (FFM)
Fat mass (FM)
Hormonal concentrations (minimal; thyroid, leptin, catecholamines)
Someone with a bigger muscle mass will burn more calories than
someone with a smaller muscle mass
FFM, age, and gender explains 80% of the variability in RMR
FFM alone has a correlation of 0.82 with RMR
RMR Measurement
Measured in post – absorptive state
Subject is:
Resting in a supine posture
Thermoneutral temperature
To Achieve these conditions, RMR measured in the morning with:
Overnight fast (8-12 hr)
Subject awake
Controlled phase of the menstrual cycle
Abstinence from exercise (12 hour)
Research problems:
Design issues – accuracy
Last bout of exercise (RMR decreases with the length of time after exercise)
Last meal (TEF/DIT)
Rested state
Low grade infections
Thermic Effect of Feeding (TEF)
What is it? Energy needed to digest, absorb and store
How is it measured? Indirect calorimetry
Factors of TEF? Fat, protein content, spiciness of food, physical activity levels
Does acute or chronic exercise affect TEF?
Some report and increase or decrease or unequal
Magnitude of TEF proportional to energy and protein content
Glycogen – depletion may elevate TEF but inconsistent reports
TEF has little impact on weight control:
In fact.. less food, less TEF
Obese: thought to have blunted TEF; however recent evidence discounts this:
meta – analysis of 50 articles