Lecture 10: Measurement Error in Dietary Intake Assessment and Special Topics

Question 1

What are the methods of assessing dietary intake and the type of measurement?

Answer 1

• 24h recall (recent intake)
• food record (recent intake)
• FFQ (usual intake)

Question 2

What is it type of bias called when the responder is concerned if they are going to be negatively judged?

Answer 2

social desirability bias

Question 3

How many days accurately measure diet?

Answer 3

It really varies, some things you need a lot of days for example, for vitamin A you need 40 days.

Question 4

What are the differences in data when you have 1 dietary recall, 2 day dietary recall and 2+?

Answer 4

• If we collect 1 dietary recall, we know that it is not a very accurate way getting a picture of what somebody is eating. So one day is the weakest level of estimation and it is inaccurate data.
• Once you take a second day like NHANES, CCHS, you will have a better estimate of the intake of your population.
• If you survey more and more, then you will get more accurate estimates.
• There are statistical ways of correcting for measurement errors.

Question 5

What are the components of dietary intake measurement error?

Answer 5

• Between-person variation
• Within-person variation
• Random error
• Systematic error

Question 6

Between vs. Within-Person Variation

Answer 6

Person A vs Person B. everyone has different diet and there will be a lot of variability between people. There is also variation within person. How I eat today vs how I eat tomorrow how I will eat next week. So, there is natural and true variability in dietary intake.

Question 7

Random Within-person error (unbiased) vs Systematic within-person error (biased)

Answer 7

Random error is unbiased. This means that some days you are going to overestimate and some days you are going to underestimate the intakes. When we take the averages of true intake and measured intake, they are pretty similar. So, this is not a bad thing and there are tools that can be applied to correct the error.

Systematic error is not something that we can correct for, it can severely impact the accuracy of our results. If you knew the true intake of this individual and average out what their caloric intake is. The lighter circles are showing what the estimate of the dietary measurement too and you can see that we are always underestimating it. So, we can say that the tool we are using is not accurate if we knew the true dietary intake was. We call this systematic error and it is biased bc it will affect your results.

Question 8

When can systematic error happen?

Answer 8

Let’s say if I wanted to reporting eating a salad. I would have to report the veggies and the dressing. If your tool doesn’t cue someone to report the dressing or doesn’t actually have a dressing reporting section. Or another example is coffee, cream and sugar, they say they had coffee, but they don’t report the cream and sugar which contribute to their energy intake.

Question 9

Why is misreporting of energy is a problem?

Answer 9

• Energy intake is a component of the diet that is substantially impacted by measurement error.

Cascade effect, if you have measurement error in the energy intake, we know that energy is tightly related to other
macronutrients and possibly micronutrient (sodium) intakes.

Question 10

Who are misreporters of energy intake?

Answer 10

• Underreporters: Dietary intake assessment yields energy intake estimates that are too low to realistically sustain a person’s energy requirements.
• Overreporters: Dietary intake assessment yields energy intake estimates that are too high to realistically reflect a person’s energy requirements.

Question 11

What is energy balance?

Answer 11

Energy balance means that you are matching the energy intake to energy balance.

Question 12

What is negative energy balance?

Answer 12

Being in negative energy balance means that you are expending more than you are taking in

Question 13

What does energy intake depend on?

Answer 13

Energy intake only depends on the intake of the person

Question 14

What does energy expenditure depend on?

Answer 14

energy expenditure has many components to it: PA, thermic effect of food, rest is also a components of physical activity and people tend to neglect that one.

Question 15

What is the basal metabolic rate?

Answer 15

• BMR represents the number of calories that a human body needs to perform basic, life-sustaining functions
o E.g. breathing, pulse, circulation, cell division, metabolism

Question 16

How to measure BMR?

Answer 16

• Experimentally can be determined using indirect calorimetry
o Assesses the amount of heat generated indirectly according to the amount of O2 consumed and CO2 released.

• Weir Equation: BMR (kcal/day) = ([VO2×3.941] + [VCO2×1.11]) ×1440

Question 17

Indirect calorimetry vs direct calorimetry

Answer 17

Direct calorimetry measurement of the amount of heat
produced by a subject enclosed within a small chamber called the isolation chamber.

Indirect calorimetry measurement of the amount of heat
produced by a subject by determination of the amount of
oxygen consumed and the amount of carbon dioxide
eliminated.

Question 18

When somebody loses weight, where does the fat go?

Answer 18

When you are losing fat, you are using your adipocytes which is an organic molecule. People talk about this as burning calories. This is an oxidation reaction, so you need oxygen for this to happen. But the end product, you have your adipose cell and, in the end, it gets converted to carbon dioxide and water. The content of that fat cell goes in the lungs and gets out as air as CO2 and O2.

Question 19

What are the prevalences in energy misreporting in dietary assessment tools?

Answer 19

• FFQs: Misreporting prevalence ~30% (underreporting specifically ~20%)
• 24-hour recalls: Can vary widely, e.g. 3 - 26% in different studies (mostly due to underreporting as well)
• Food records: if participant records accurately, little likelihood of energy misreporting

** 24-hour recall it varies but might depend on the interviewer, their skills, how well they were trained. Food record: if it is reported by your participant then you shouldn’t be missing anything but that is a big if bc sometimes the participants are not as accurate bc of the social desirability bias, memory, time limit, etc. food records, in theory, shouldn’t be affected by misreporting but in reality they are.

Question 20

How to identify misreporters?

Answer 20

• Goldberg method: Based on the principle that, when a healthy individual is in energy balance: o Energy Intake (EI) = BMR*Physical Activity Level (PAL)
• Rearranging the equation yields: o EI/BMR = PAL

Question 21

Explain the Goldberg method

Answer 21

• Evaluates plausibility of EI by constructing a confidence interval:
• E.g. If Goldberg method produced a plausible CI of (975 kcal, 2,845 kcal) a person consuming ≤975 kcal/d would be considered under-
reporter, ≥2,845 kcal/d would be considered over-reporter.

Question 22

How to estimate the components of Goldberg method

Answer 22

• Energy intake estimated from dietary assessment tool
• BMR estimated by equations that have been validated against indirect calorimetry studies (e.g. Mifflin)
• It important to calculate Goldberg cut-offs for men and women separately
• Physical activity level: use standard cut-offs
o These values have been obtained from studies measuring energy expenditure using doubly labelled water
• Value S: use predetermined values noted in Goldberg method (Goldberg et al. Eur J Clin Nutr. 1991 Dec;45 (12):569-81.)
• Std Dev: use +/-2 to achieve a 95% CI

Question 23

Explain the doubly labelled water

Answer 23

Subject will drink this doubly labelled water. It is called that because there is two of the isotopes of hydrogen in this water which is called deuterium. Somebody drinks this water dose, and it equilibrates which means that it will combine and mix with the regular water in someone’s body but bc it is different from regular water, when you excrete it the two H2 is eliminated separately from the oxygen. So, you measure the urine excretion. You can recover the hydrogen isotopes in the water from the urine and subtract them, you eliminate the water component, so you are left with CO2 which is the by-product of energy expenditure. So, it is a good estimate of how much calories have been used by this individual (PAL)

Question 24

What are the consequences of energy misreporting?

Answer 24

• Under-or over-estimation of nutrient intakes-> problematic when assessing diet-health relationships
• Particularly an issue for nutrients that are strongly correlated to caloric intake

Question 25

Explain how energy misreporting dampens statistical associations?

Answer 25

The black line shows that if we had really nice dietary data this would be the slope of the line. The blue dashed line shows what would happen if you had weak dietary data. You can see that this relationship is weakened. This is a regression model, why is the blue line is weaker than black line? Which one of these scenarios have a bigger beta value? The black line. If the slope gets closer to zero you have a weaker relationship bc the null hypothesis is beta = 0 in linear regression tests.

How close the points are to the line is correlation? Even if you have all
the points lined up exactly on the line which is perfect correlation of
100% but that doesn’t mean that you have a statistically significant relationship bc correlation is not the same thing as slope.

Question 26

How to mitigate misreporting?

Answer 26

• Use a validated dietary assessment tool

• Obtain weight, height, and physical activity data in nutrition studies
o In order to assess misreporting prevalence

• Obtain information on weight loss intention
o In order to assess assumption of energy balance

• Investigate dietary patterns
o Role of energy intake less relevant

• Statistical methods to reduce measurement error
o (correct for random within-person variation)

Question 27

What are the types of genetic information? Give example.

Answer 27

• Disease associations
o Alzheimer’s disease: 1 APOE gene mutation
o Breast cancer: 3 BRCA gene mutations
o T2D: mutations in 1000s of genes

• Traits (some referred to as “Wellness”)
o Bitter taste perception: 1 TAS2R38 gene mutation
o Caffeine metabolism: 1 CYP1A2 gene mutations
o Body mass index: mutations in 100s of genes

Question 28

Where does the evidence come from? Disease Associations

Answer 28

• American College of Medical Genetics and Genomics (ACMG)
• ClinVar
• SNPedia

Question 29

American College of Medical Genetics and Genomics (ACMG)

Answer 29

o ACMG 59: list of 59 medically actionable genetic variants
that are known/expected to cause monogenic diseases
o 5-point classification system:
- Known Pathogenic,
- Expected Pathogenic,
- Variant of Unknown Significance (VUS),
- Expected Benign,
- Known Benign

Question 30

ClinVar

Answer 30

“Freely accessible, public archive of reports of the relationships among human variations and phenotypes hosted by the National Center for Biotechnology Information (NCBI) and funded by intramural National Institutes of Health (NIH) funding.”

Question 31

SNPedia

Answer 31

“…a wiki investigating human genetics. We share information about the effects of variations in DNA, citing
peer-reviewed scientific publications. It is used by Promethease to create a personal report linking your DNA variations to the information published about them.”’

Question 32

Where does the evidence come from? Traits/Wellness

Answer 32

• Published Literature

* SNPedia

Question 33

Why is understanding genomic associations: a moving target?

Answer 33

• Variant reclassification
o CMG 59 list will likely change over time
o ACMG 56 in 2013: 1 variant reclassified to VUS, 4 new variants added as Known or Expected Pathogenic

• Third party genomic reinterpretation websites
o promethease.com
o “literature retrieval system that creates a personal DNA report based on your DNA data, taking into account all the scientific and medical literature cited in SNPedia. Customers of DNA testing services use Promethease to learn more about their DNA variants, independent of whichever company produced the raw DNA data.”