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Nutrition and Metabolism > Caloric and Isotopic methods > Flashcards

Caloric and Isotopic methods Flashcards

1
Q

What is the energy balance equation?

A

Energy intake = Energy expenditure ± ∆ stores

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2
Q

What has to be measured when we want to involve the energy balance equation?

A

energy intake and expenditure

and body composition

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3
Q

what are the major difficulties in measuring energy intake?

A
  • qualitative/quantitative description of intake
  • reliability of reference data
  • deliberate and unconscious bias
  • indirect recording for infants/toddlers
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4
Q

What are the fundamental energetics of any biological system?

A

Energy in = Energy out ± Δ Energy content

Total work done is INDEPENDENT of pathways

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5
Q

What are the possible types of energy in the body?

A
  • chemical
  • urinal/faecal
  • mechanical
  • electrical
  • thermal
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6
Q

As an outcome of metabolism to result in ‘work’… what is produced?

A

heat

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7
Q

What did Boyle investigate regarding calorimetry methods?

A

fire and life are combustion processes

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8
Q

What did Lavoiser and Laplace investigate regarding calorimetry methods?

A

CO2 and heat production

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9
Q

What did Magnus investigate regarding calorimetry methods?

A

arteries have increased O2 and decreased CO2

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10
Q

What did Helmholtz investigate regarding calorimetry methods?

A

heat produced by isolated muscle

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11
Q

What did Lavoisier (on his own) investigate regarding calorimetry methods?

A

digestion, PA and cold increase VO2

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12
Q

What did Regnault and Reiset investigate regarding calorimetry methods?

A

Ratio of CO2 and O2 in gas exchange related to dietary composition

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13
Q

What also defines Joule?

A

watts per second

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14
Q

what is the SI unit of Joules?

A

kg/m2/s2

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15
Q

What defines calorie?

A

the heat required to raise 1g water by 1^C

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16
Q

How much is 1 kcal in J?

A

4.184

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17
Q

What are the current 4 modern approaches to total energy expenditure?

A
  1. Douglas bag - fast, but unrepresentative
  2. Indirect calorimetry - accurate, fast, but constrained
  3. Direct calorimetry - accurate, fast, but constrained
  4. Doubly labelled water - accurate, free-living but slow response
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18
Q

What is SMR?

A
  • sleeping

- replaces the RMR for infants

19
Q

What does the classical indirect calorimetry involve?

A
  • standardised conditions
  • assumes steady state
  • BMR, RMR, SMR
  • studies of physiology
20
Q

What are the output results from indirect calorimetry method?

A
  • oxygen uptake
  • carbon dioxide production
  • resting energy expenditure
  • fuel utilisation (RQ)
21
Q

What is the EE formula for indirect calorimetry?

A

EE = 3.941 VO2 + 1.106 VCO2 - 2.17 Un

Un = urea nitrogen production

22
Q

How much % is the effect of neglecting nitrogen in EE?

A

1%

23
Q

Give the general understanding of doubly labelled water:

A
  • uses isotopes 2^H and 18^H
  • traces the kinetics of H2O and CO2
  • estimates CO2 elimination rate
24
Q

What is the key principle in doubly labelled water?

A

O2 in respiratory CO2 is in isotopic equilibrium with O2 in body water

25
Q

What is collected in doubly labelled water method, to analyse?

A

blood, saliva, urine samples

26
Q

What is the formula for the expression of isotopic enrichment, the mass spectrometer analysis?

A

δ = [R(sample) - R(reference) x 1000] DIVIDED BY R(reference)

27
Q

What is the fundamental calculation for rCO2, in DLW?

A

rCO2 = N [k(o) - k(d)]/2

N = dilution space
k = rate constant
28
Q

What is the fundamental calculation for VO2, in DLW?

A

VO2 = VCO2/RQ

29
Q

What is the fundamental calculation for TEE, in DLW?

A

TEE = k(1)VO2 + K(2)VCO2

30
Q

What are the assumptions of DLW?

A
  • TBW is constant
  • isotopes only equilibrate with TBW
  • Isotopes only leave as water or CO2
  • rates of influx and efflux constant during measurement
  • no isotopic fractionation
  • no tracer re-enters TBW once lost
  • natural isotopic levels unchanged
31
Q

What are the two approaches in calculating dilution spaces (N) in DLW?

A
  • plateau method

- back extrapolation method

32
Q

What is the plateau result when isotope turnover is slow?

A

plateau is relatively stable

33
Q

What is the plateau result when isotope turnover is fast?

A
  • plateau occurs at specific time

- tracee intake during equilibration period is high

34
Q

Which named approach reduces error in the rCO2 calculation in DLW?

A

Bayesian approach

35
Q

Is there fractionation in DLW?

A

only possible in reaction not going to completion

36
Q

what is the calculation for fractionation factor (f)?

A

(f) = [Ratio of heavy : light isotopes in product] DIVIDE BY [Ratio of heavy : light isotopes in reactant]

37
Q

Explain why isotopic intake is not constant

A
  • 2^H and 18^O occur at natural abundance levels
  • levels vary by diet, geographic location
  • Pre-dose sample provides this information
38
Q

What is the random variability in DLW?

A

50% internal imprecision

39
Q

what is the systemic variability in DLW?

A
  • weaning in infants
  • expedition in adults
  • marked dietary interventions
40
Q

How do we address the precision of EE internally, in DLW?

A
  • calculate in relation to slopes and intercepts

- address sample times and mass spec

41
Q

How do we address the precision of EE externally, in DLW?

A

address consistency of behaviour

42
Q

What is the formula for lean mass, in regards to body composition from isotopes?

A

Lean mass = Total body water/lean tissue hydration

43
Q

What is the formula for fat mass, in regards to body composition from isotopes?

A

= weight - lean mass

44
Q

What is the measuring metabolisable energy intake (MEi) formula?

A

MEi = Total energy expenditure + energy stored

Nutrition and Metabolism (14 decks)

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