Week 5: LEC 8&9 Flashcards
(10 cards)
Assessing the intakes of groups using the DRIs
LEC 8
** NOTE on slide 5 **
WHY would you want to know about the diet of a group? ->
Adjusting the intake distribution
-> Typically, group intake data is collected thru…
-> Usually, the nutrient intakes of a group from a normal distribution (bell-shaped) = AKA =
-> Variability within the intake distribution has…
-
-
* see visual graph slide 9 *
-> removing within-person variability (‘adjusting’) you get:
-> To create guidelines/ to understand if population is vulnerable or at risk / to create intervention or know how to target an intervention or education
-> … thru 24 recalls or food records
ie. in the CCHS
= intake distribution
…has 2 sources:
- within-person (intra-individual) variability
- between person (inter-individual) variability
: you get less variation affecting the curve / not adjusted = wide variation - may over or under assume intakes
Adjusting the intake distribution
> Day-to-day variation gets in the way of examining usual intake
> Adjusting the intake distribution by removing within-person variability does not change the mean but it decreases the SD
> If the intake distribution is not adjusted to reflect usual intakes, the prevalence of inadequate intakes may be overestimated
HOW is the intake distribution adjusted?
-> To remove within-person variability (to more closely reflect usual intakes) you need…
- this tells you how much:
-> multiple days of data from at least a representative subsample of the group
: day-to-day variation there is in your population (how much needs to be adjusted for)
Assessing prevalence of inadequacy
-> To assess the prevalence of inadequacy in groups, we need to use:
-
-
-> 2 methods can be used to determine the prevalence of inadequacy:
1
2
The EAR cut-point method
-> Simply calculate…
-> The percentage of intakes below the EAR is…
EXAMPLE - slide 18
[How does it work] - slide 18
- The adjusted intake distribution that reflects usual intake of groups
- The requirement distribution used to set the EAR
1 The EAR cut-point method
- this is commonly used shortcut
2 The full probability method
- just like what we did with individuals last class
-> … the proportion (or %) of the group with intakes less than the EAR
-> … a good estimate of the percentage of the group with intakes below their requirements
Points to keep in mind:
-> Assumptions of the EAR cut-point method
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-
-
> When using the EAR cut-point method, we can’t determine the specific individuals whose intakes are inadequate… WHY?
1
2
[these 2 groups are expected to cancel eachother out]
- the prevalence of inadequacy in the group can thus be approximated by the proportion with usual intakes below the EAR
- Intakes and requirements must be independent (not be correlated)
- this is not true for energy
- The distribution of requirements must be symmetrical
- this is not true of iron
- The distribution of intakes must be more variable than the distribution of requirements
- thought to be true among groups of free-living indiv
- this may not be true for groups who have very similar diets (ie. residents in LTC, prison inmates)
? 1 some ppl with intakes below the EAR have lower than avg requirements
2 some people with intakes above the EAR have higher than avg requirements
The Full Probability Method for groups
1
2
The Full Probability Approach method depends on 2 key assumptions:
->
->
EXAMPLE - slide 24 ***
READ ** What about Iron - SLIDES 26-27 & 30 **
EXAMPLE slide 28/29 ***
1 - Calculate the probability of inadequacy of the usual intake level for each person in the group
- if you have 200 participants, that means 200 z-score calculations
-> Intakes and requirements are independent, and thus no correlation exists between usual intakes and requirements
- this is thought to be true for most nutrients, although it is not known to be true for energy
-> The distribution of requirements for the nutrient in questions is known
[this method uses statistical eqns to estimate the prevalence of inadequacy]
2 - Calculate the avg of these individual probabilities across the group
- this avg is a good estimate of the % of people who would have inadequate intakes
Do not use the RDA for groups
-> It is not appropriate to use…
-> Comparing the mean intake of the group…
What about nutrients with an AI?
-> If a nutrient has an AI…
-> You can…
interpretations [ ]
NOTE: in this case you don’t need to adjust the distribution of intakes for day-to-day variability
- removing variability doesn’t alter the mean but decreases the standard deviation
-> … use the RDA as a cut-point for groups b/c it overestimates the requirements of 97-98% of the population
- many indiv have requirements below the RDA and therefore cannot be assumed to be deficient if intake is below the RDA
-> … to the RDA is also inappropriate
-> AI … you cannot estimate prevalence of inadequacy b/c the distribution of requirements is not known
- do not use the AI as a cut-point like the EAR
-> you can… compare the mean intake of the group to the AI and make a qualitative interpretation
[ mean intake < AI = nothing can be concluded about inadequacy /// mean intake >/= AI = prevalence of inadequacy is likely low]
What about nutrients with a UL?
-> Calculate the…
-> Remember that the UL for some nutrients doesn’t apply to intake from all food sources: __, ___, ___, __
EXAMPLE - slide 35 ***
What about nutrients with an AMDR?
> You can calculate the proportions of the group that fall below, within and above the AMDR
> If lg proportion of the population has usual intakes outside the AMDR range, there is increased concern about possible adverse health effects - chronic diseases
-> … proportion (or %) of the group with intakes above the UL
- the proportion of the group with usual intakes exceeding the UL may be at risk for adverse health effects
-> Mg, Vit E, Niacin, Folate
Assessing energy adequacy
-> The EAR cut-point method and full probability approach cannot be used to assess energy intakes
- Reason:
-> BMI is preferred for assessing the adequacy of energy of a group
- calc proportions of the group with BMIs below, within and above the desirable range
General Reminder…
[DRIs and nutrient intake estimates have limitations]
- Findings of inadequacy or excess need to be confirmed with other measures or nutrition status (ie. anthropometrics, biochemical tests)
Planning nutrient intakes for groups
> Menu planning for groups is important in many settings: Prisons / Hospitals / LTC / Child nutr and food assistance programs
Planning Menus
> Simply comparing mean intake of the group to the RDA is inappropriate
- The GOAL is to…
- : energy intakes and energy requirements are correlated (not independent)
- … is to have low prevalence of inadequate or excessive intakes
- usually aim for 2-3% of intakes < EAR and 2-3% of intakes > UL
Step 1: Determining the current intake distribution
-> This may mean:
-> If you cannot do a dietary assessment - you can -
-> Look at the intake distribution and determine how many people have intakes below the EAR : ex on graph - slide 42
Step 2: Setting a target distribution
->
- EX
(GRAPH slides 44-45 explaining)
-> : doing a dietary assessment to determine what your population is currently eating
EX: in LTC - record intake of residents for # of days and analyse intakes
- you can use population data for your age group of interest (CCHS, NHANES)
-> Determine how much you would have to move the distribution so that only 2-3% of your population would have intakes below the EAR
- EX - if we increased everyone’s intake by 5mg only, 2-3% of the pop would have intakes below the EAR
Step 3: Planning your menu
> You can use the new median of the target distribution as a goal when planning menus
- continuing the ex above, if the new target median was 20mg - you would plan a menu where avg portion sizes would result in…
EXAMPLE - slide 47
What if intakes are too high?
-> If there is a high prevalence of intakes above the UL, use the…
Other criteria for menu planning
-> For nutrients with an AI…
-> For energy intake…
-> Aim for group to stay within the…
Menu planning is an ongoing process…
Set goals for usual intake / implement the plan / evaluate whether goals were achieved / modify the plan
- … in an intake of 20mg per day
-> … same approach to create a target distribution with only 2-3 % of the group having intakes above the UL
-> AI… set a goal for median intake to equal the AI
-> … set a goal to provide the mean EER for the group
-> AMDRs
