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HUNT242 > Lecture 18 > Flashcards

Lecture 18 Flashcards

Dietary assessment challenges and how to overcome them

1
Q

it is quite common for people to report very low energy intakes when reporting what they eat. if they are under reporting their energy can we believe their nutrient intakes

A

no not really

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2
Q

what is under reporting

A

deliberate or unintentional omission of underestimation of foods

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3
Q

what is under-eating

A

process of diet reporting can make people change their eating habits

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4
Q

what is the mean intake of a 19-30y old male from the adult nutrition survey (2008)

A

11.9MJ

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5
Q

what is the mean intake of a 19-30y old female from the adult nutrition survey (2008)

A

8.4MJ

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6
Q

what is a method of identifying low energy reporters

A

“doubly labeled water”

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7
Q

doubly labeled water technique can determine

A

degree of diet underestimation

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8
Q

how accurate is doubly labelled water

A

very accurate estimation of free living energy expenditure (only 1-2% error)

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9
Q

what is meant by energy balance in terms of dietary assessment

A

if they are in energy balance

the energy they report to be eating should be = to their energy expenditure

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10
Q

what are 3 forms of indirect calorimetry

A
  • douglas bag
  • portable gas analysis
  • on line gas analysis
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11
Q

what does doubly labelled water contain

A

stable isotopes : deuterium and oxygen 18

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12
Q

what does doubly labelled water estimate

A

CO2 production without needing breathing apparatus

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13
Q

how does doubly labelled water work

A

drink a small amount of doubly labelled water and collect urine samples to determine how quickly isotopes disappear from body

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14
Q

what are the two ways we lose oxygen from the body

A

through urine and breathing out CO2

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15
Q

how do we know how much of the doubly labelled water is lost through CO2 without a breathing apparatus

A

measure the amount of oxygen lost in the urine, calculate difference by the doubly labelled water oxygen that wasnt lost in urine

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16
Q

what happens to the doubly labelled water when it enters your body

A

labels the water pool, evenly disperse in your body

17
Q

once you know how much CO2 is exhaled from the doubly labelled water, can use that to

A

calculate energy expenditure and then you can compare this to the energy they have reported and this should be the same if they are in energy balance

18
Q

what are the advantages to doubly labelled water

A
  • once you know CO2 losses for time period can calculate total energy expenditure
  • if in energy balance then reported energy intake should = energy expenditure
  • very accurate
  • relatively simple for participant
19
Q

what are the disadvantages to doubly labelled water

A
  • very expensive
  • only get average total energy expenditure (not for individual days)
  • assumes energy balance so amount of energy expended = amount eaten
20
Q

what are the steps to using doubly labelled water to identifying low energy reporters

A
  1. collect dietary data
  2. measure energy expenditure by doubly labelled water at the same time
  3. calculate difference
21
Q

the doubly labelled water method can be expensive and inconvenient so what can be used instead

A

equations based on estimated basic energy requirements

basal metabolic rate + allowance for basic activities of daily life (usually assumes a sedentary lifestyle)

22
Q

the goldburg equation allows you to determine whether

A

reported intake is high enough to represent : plausible intake for the period measured

23
Q

in the goldburg equation intakes vary day to day so the cut off ….

A

the cut off to determine plausible intake is lower than it would need to be to determine whether intake represents habitual intake

24
Q

what are the steps to using the goldburg equation

A
  1. collect data on : energy intake, sex, age, weight for each individual
  2. calculate estimated basal metabolic rate for each individual using Schofield et al (1985)
  3. use goldburg equation et al (1991) to determine cut off value for 1 person with data collected over x days
  4. low energy reporting is indicated if EI:BMRest < cutoff
25
Q

what are the advantages to the goldburg equation

A
  • quick, easy, cheap
  • can be done retrospectively if have age, sex and weight
  • non invasive
26
Q

what are the disadvantages to the goldburg equation

A
  • not as accurate as DLW - misses some LERs
  • assumes participants are in energy balance
  • assumes sedentary level physical activity
27
Q

what happens if you delete participants with low energy reporting

A
  • misses people who have high intakes who are LER
  • LERs have other characteristics e.g overweight, higher social desirability so could > bias
  • we dont measure HERs
28
Q

what happens if we keep participants of low energy reporting but report the prevalence

A

keeps data that are inaccurate

29
Q

what should we do with low energy reporters

A

collect data to quantify LER

minimise risk of low energy reporters

30
Q

what are biomarkers

A

substances in biological specimens such as blood, urine of hair which reflect intake sufficiently closely to act as objective indices of true intake

31
Q

examples of biomarkers and their use

A

doubly labelled water = energy

24hr urine nitrogen = protein

adipose fatty acids = some fatty acids

32
Q

biomarkers are independent of

A

many errors associated with dietary methods

33
Q

biomarkers can be used to

A
  • assess measurement error (how well the dietary assessment is working)
  • calibrate measurement error in dietary data
34
Q

why not use biomarkers instead of dietary assessment ?

A
  • only available for some nutrients
  • often expensive
  • invasive
  • transport and storage issues
  • assumptions
  • dont necessarily capture total intake
  • generally reflect recent intake only
  • may be affected by disease status
35
Q

why are biomarkers invasive

A
  • biological specimens
  • complete collection required
  • multiple collections may be required
36
Q

what are some assumptions of biomarkers

A
  • doubly labelled water assumes energy balance
  • 24hr urine nitrogen assumes nitrogen balance
37
Q

what is meant by biomarkers don’t necessarily capture total intake

A
  • low energy reporters are often under collectors
  • urine nitrogen ~80% intake

HUNT242 (15 decks)

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