Lecture 18: Dietary Assessment Challenges

Question 1

What is low energy reporting?

Answer 1

When people report very low energy intakes
- May be under-reporting or under-eating

Question 2

What is under-reporting?

Answer 2

Deliberate or unintentional omission or underestimation of foods

Question 3

What is under-eating?

Answer 3

Process of diet reporting can make people change their eating habits

Question 4

What are mean adult energy intakes (Adult Nutrition Survey 2008)?

Answer 4

Males (19-30y) = 11.9 MJ
Females (19-30y) = 8.4 MJ

Question 5

How can we identify low energy reporters?

Answer 5

Doubly Labeled water (DLW) or Goldberg Equation

Question 6

What is DLW error?

Answer 6

Very accurate (only 1-2% error)

Question 7

What is energy balance?

Answer 7

Energy in = Energy out

Question 8

What is energy in?

Answer 8

Reported energy intake

Question 9

What is energy out?

Answer 9

Energy expenditure

Question 10

How are carbohydrates metabolised?

Answer 10

Use 6 oxygen -> produce 6 carbon dioxide

Question 11

How is fat metabolised?

Answer 11

Use 23 oxygen -> produce 16 carbon dioxide

Question 12

What are both CHO and Fat equations the basis of?

Answer 12

Indirect calorimetry

Question 13

What is indirect calorimetry?

Answer 13

Measuring oxygen going in and carbon dioxide coming out to figure out how much energy was expended and metabolised

Question 14

What are stable isotopes used for doubly labelled water?

Answer 14

Deuterium and oxygen-18

Question 15

What is deuterium?

Answer 15

Stable isotope of hydrogen (added neutron)

Question 16

What is oxygen-18?

Answer 16

Stable isotope of oxygen (2 added neutrons)

Question 17

What does double labelled water estimate?

Answer 17

CO2 production without needed breathing apparatus

Question 18

How does doubly labelled water work?

Answer 18

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

Question 19

What does deuterium attach to?

Answer 19

onto H2

Question 20

What does oxygen-18 attach onto?

Answer 20

Oxygen (O)

Question 21

What are advantages of DLW?

Answer 21

• 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

Question 22

What are disadvantages of DLW?

Answer 22

• Very expensive
• Only get average total energy expenditure (not for ind days)
• Assumes energy balance

Question 23

How do we use DLW to identify LER?

Answer 23

1. Collect dietary data
2. Measure energy expenditure by DLW at the same time
3. Calculate difference

Question 24

How can we identify low energy reporters when DLW is inconvenient or too expensive?

Answer 24

Equations can be used based on estimated basic energy requirements e.g. Goldberg Equation

Question 25

How does the Goldberg equation allow you to determine?

Answer 25

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

Question 26

Why is cutoff to determine plausible intake lower than it would need to be?

Answer 26

To determine whether intake represents habitual intake - varied intake from day to day

Question 27

What are advantages to the Goldberg equation?

Answer 27

- Quick, easy, cheap - Can be done retrospectively if have age, sex and weight - Non-invasive

Question 28

What are disadvantages of the Goldberg equation?

Answer 28

- Not as accurate as DLW (misses some LERs) - Assumes participants are in energy balance - Assumes sedentary level PA

Question 29

What are options for dealing with low energy reporting data?

Answer 29

- Delete participants - Keep participants but report prevalence - Collect data to quantify LER

Question 30

What are biomarkers?

Answer 30

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

Question 31

Why use biomarkers?

Answer 31

They are independent of many errors associated with dietary methods

Question 32

Biomarkers can be used to...

Answer 32

- Assess measurement error - Calibrate measurement error in dietary data

Question 33

Why not use biomarkers instead of dietary assessment?

Answer 33

- Only available for some nutrients - Often expensive - Invasive - Transport and storage issues

Question 34

How are biomarkers invasive?

Answer 34

- Biological specimens - Complete collection required - Multiple collections may be required

Question 35

What are disadvantages to using biomarkers?

Answer 35

- Many assumptions - Don't necessarily capture total intake - Generally reflect recent intake only - May be affected by disease status

Question 36

How don't biomarkers capture total intake?

Answer 36

- LER's are often under-collectors of biological samples - Urine nitrogen will only. show approx. 80% of intake

Question 37

What methods can be used to identify LERs?

Answer 37

Doubly labelled water or the Goldberg equation

Question 38

Biomarkers are useful adjuncts to dietary assessment but...

Answer 38

Do not replace them

Question 39

LER is not necessarily...

Answer 39

Intentional