Lecture 18: Dietary Assessment Challenges Flashcards
What is low energy reporting?
When people report very low energy intakes
- May be under-reporting or under-eating
What is under-reporting?
Deliberate or unintentional omission or underestimation of foods
What is under-eating?
Process of diet reporting can make people change their eating habits
What are mean adult energy intakes (Adult Nutrition Survey 2008)?
Males (19-30y) = 11.9 MJ
Females (19-30y) = 8.4 MJ
How can we identify low energy reporters?
Doubly Labeled water (DLW) or Goldberg Equation
What is DLW error?
Very accurate (only 1-2% error)
What is energy balance?
Energy in = Energy out
What is energy in?
Reported energy intake
What is energy out?
Energy expenditure
How are carbohydrates metabolised?
Use 6 oxygen -> produce 6 carbon dioxide
How is fat metabolised?
Use 23 oxygen -> produce 16 carbon dioxide
What are both CHO and Fat equations the basis of?
Indirect calorimetry
What is indirect calorimetry?
Measuring oxygen going in and carbon dioxide coming out to figure out how much energy was expended and metabolised
What are stable isotopes used for doubly labelled water?
Deuterium and oxygen-18
What is deuterium?
Stable isotope of hydrogen (added neutron)
What is oxygen-18?
Stable isotope of oxygen (2 added neutrons)
What does double labelled water estimate?
CO2 production without needed breathing apparatus
How does doubly labelled water work?
Drink a small amount of labelled water with both isotopes on them and collect urine samples to determine how quickly isotopes disappear from the body
- Isotopes weigh a different amount so you can measure them
What does deuterium attach to?
onto H2
What does oxygen-18 attach onto?
Oxygen (O)
What are advantages of DLW?
- Once 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
What are disadvantages of DLW?
- Very expensive
- Only get average total energy expenditure (not for ind days)
- Assumes energy balance
How do we use DLW to identify LER?
- Collect dietary data
- Measure energy expenditure by DLW at the same time
- Calculate difference
How can we identify low energy reporters when DLW is inconvenient or too expensive?
Equations can be used based on estimated basic energy requirements e.g. Goldberg Equation
How does the Goldberg equation allow you to determine?
Whether reported intake is high enough to represent the plausible intake for the time period measured
Why is cutoff to determine plausible intake lower than it would need to be?
To determine whether intake represents habitual intake - varied intake from day to day
What are advantages to the Goldberg equation?
- Quick, easy, cheap
- Can be done retrospectively if have age, sex and weight
- Non-invasive
What are disadvantages of the Goldberg equation?
- Not as accurate as DLW (misses some LERs)
- Assumes participants are in energy balance
- Assumes sedentary level PA
What are options for dealing with low energy reporting data?
- Delete participants
- Keep participants but report prevalence
- Collect data to quantify LER
What are biomarkers?
Substances in biological specimens such as blood, urine or hair which reflect intake sufficiently closely to act as objective indices of true intake
Why use biomarkers?
They are independent of many errors associated with dietary methods
Biomarkers can be used to…
- Assess measurement error
- Calibrate measurement error in dietary data
Why not use biomarkers instead of dietary assessment?
- Only available for some nutrients
- Often expensive
- Invasive
- Transport and storage issues
How are biomarkers invasive?
- Biological specimens
- Complete collection required
- Multiple collections may be required
What are disadvantages to using biomarkers?
- Many assumptions
- Don’t necessarily capture total intake
- Generally reflect recent intake only
- May be affected by disease status
How don’t biomarkers capture total intake?
- LER’s are often under-collectors of biological samples
- Urine nitrogen will only. show approx. 80% of intake
What methods can be used to identify LERs?
Doubly labelled water or the Goldberg equation
Biomarkers are useful adjuncts to dietary assessment but…
Do not replace them
LER is not necessarily…
Intentional
