Dietary assessment Flashcards
What are the four main methods of dietary assessment?
- 24 hour recalls
- Diet record
- FFQ
- Diet history
Why use dietary assessment?
- Examine nutrient intake
- Look at specific foods/ food groups
- Examine dietary patterns
___ in ____ toddlers are iron deficient
1 in 3
How much can fortified milk increase toddler’s iron status by?
~122% (though subconsciously reduced red meat)
How do you carry out a dietary assessment recall?
- Develop a quick list
- Probe for forgotten foods
- Obtain food details (cooking method, time, brand)
- Obtain portion size (familiar measures)
- Final review (last chance to collect info on food not remembered)
What is the goal of a 24 hour diet recall?
Capture actual intake over a pre-specified time
What different types of diet recalls are there?
+ paper or online
+ can use interviewer or self-administered
What are the limitations of a diet record?
- have to carry measuring equipment & diet record
- have to ask about contents of food
- may change way someone eats
What is a food frequency questionnaire used for?
To measure usual or habitual intake (assess the frequency of intake of certain foods & look at specific dietary sources of nutrients)
What is one important consideration to take into account when when carrying out FFQ’s?
Must be validated for population it is going to be used in.
What is a diet history?
A fact to face interview (similar to a diet recall) that asks about variations over a week to help gain understanding of someone’s usual intake.
What is a diet history usually evaluated against
Recommended servings (i.e. of alcohol & salt)
What are key things to consider when conducting a dietary assessment?
- All responses are confidential
- Be non-judgemental
- Do not ask leading questions (portion sizes, breakfast etc..)
- Accuracy of information is very important
What are sources of error in a dietary assessment?
+ Change what you report (interviewer judgemental)
+ forgot what you ate
+ hard to estimate portions
+ raw/cooked weight?
+ ignoring drinks
+ people not volunteering cause not interested (bias)
+ unsocially acceptable cause misrepresentations
What are food composition databases?
+ average nutrient content of wide ray of foods
+ NZ Foodfiles
What is validity?
The extent to which a method gives you the “correct” answer
What is the difference between relative & absolute validity?
Absolute requires precise measurement of intake, whilst relative validity is indirect.
What is Reliability/ Repeatability?
The extent which a method gives you a reproducible answer
What is accuracy?
Accuracy is the e extent to which the measurement is close to the true value
What is measurement error?
Difference between measured & true value
What is observed intake?
True intake + measurement error
What are the 2 types of measurement error?
Random & systematic error
What does measurement error lead too?
Attenuation of relationships & Bias
What is random error?
Error due to chance/ normal variation which leads to increased variability around the mean & decreased variability
(Doesn’t change Mean)
What are some sources of s error?
a) Non-response bias
b) Respondent bias
c) Interviewer bias
d) Respondent memory lapses
e) Incorrect estimation portion size
f) Omission of supplements
g) [Coding and computation errors]
h) [Errors in handling mixed dishes]
i) [Errors in food composition database]
What is non-response bias?
When a specific sub-set of people don’t volunteer to participate, adhere to the intervention or drop out.
What does non-response bias cause?
A non-representative sample (under/ over estimates effect)
What are some strategies to minimise non-response Bias?
- Minimize respondent burden
- Mail or phone reminders
- Offer material rewards
- Train interviewers so warm and trusted
- Identify non-responders and characterize
- Over-sample groups at risk of non-responding
What is Respondent Bias & the three main types?
Bias introduced by the Respondent
- Low energy Reporting
- Over reporting
- Social desirability
What are some strategies to minimise respondent bias?
• Pre-test methods (cognitive interviewing?)
• Interviewer training
• Private interviews
• Identify flawed data (e.g. Goldberg equations)
• Identify participants at risk:
Ø Social desirability scale
Ø Dietary restraint scale (e.g. Eating Inventory)
What is interviewer bias & the 3 main causes?
Bias introduced by the interviewer Caused by: \+ Incorrect recording \+ intentional omissions \+ poor cultural sensitivity
What are some strategies to minimise interviewer bias?
Strategies: • Standardized computer interviews • Train interviewers: Ø Avoid value judgments Ø Culturally safe Ø Pace • Identify problem interviewers: Ø Multiple interviewers same interviewees Ø Mean energy intake per interviewer
What are respondent memory lapses?
- Errors of Omission
2. Errors of Commission
Who is respondent memory lapses more likely in?
- Longer time period to be recalled
- Men
- Age extremes
- distracting environment
What are strategies to minimise respondent memory lapses?
Multiple-pass interviewing techniques
Ø Free uninterrupted recall
Ø Probe questions
• Minimize time between intake and recall
• Work with information retrieval, e.g., <8yrs of age:
Ø Visual imagery
Ø Usual practice
What is incorrect portion estimation?
Failure to accurately quantify amount eaten
What is the largest source of systematic error?
Incorrect portion estimation
What are strategies to minimise incorrect portion estimation?
- Measurement aids:
- Train interviewers
- Train respondents
What does supplement omission lead too?
Systematic underestimation of nutrient intake
Ø Overestimation of prevalence inadequacy
What are strategies to minimise supplement omission?
• Structured questionnaire on long-term intake • Close-ended questions on: Ø Brand Ø Amount per pill Ø Frequency of use Ø Duration of use Ø Chemical form of supplement • Interviewer sights supplement
What is sensitivity?
How good the test/method is
at correctly identifying people who have the
disease/low status
What is specificity?
How good the test/method is
at correctly identifying people who are
well/have adequate status
What are sources of error in portion estimation?
- Memory/recall • Incorrect use of portion size tools (Interviewer)
- Quantification skills of respondent
- Density factors
What cognitive processed effect portion size estimation?
- Perception- amount in relation to aid
- Conceptualization- amount not present
- Memory
PLUS
• Social desirability
What are some portion size estimation tools?
- Household measures
- Standard measurement units: g, kg, ml, ounces, pounds
- Known packaging size
- Visual aids e.g. diagrams, photos, food atlas
- Categorical size estimations: small, medium or large
- Food models
- Hands
- Beans, water- measuring cylinders
What are different ways diet recall can be administered?
+ in home; clinic; school; or workplace
+ Interviewer administered/ self-administered
+ Computer based self- administered recalls
What factors influence portion size estimation?
- dietary assessment method
- Type of Food
- Respondent characteristics
What is the recipe dilemma?
- Ingredients
- Quantities • Before cooking
- Yield after cooking
- % consumed by participant
- Only Part eaten?
What is the flat slope phenomenon?
Large portions are underestimation & small portions are underestimated
_______ food is more difficult to estimate than single unit food
Amorphous
consumers estimate ______ portion size if the packet is larger
Larger
What respondent characteristics influence portion estimation?
Ethnicity/ culture (shared dishes; different utensils; eat with hands)
Literacy & numeracy
Age (memory & cognitive development)
How does literacy effect serving size?
High literacy increases accuracy 2.5 x
Why does food not always = nutrients?
Personal & broader meanings to food that we are often not aware of
What do the meanings we associate food impact?
What, how & when we eat
What are the implications behind food meanings?
May impact accuracy
+ food composition data may be unreflective
+ habitual or regular intake?
+ may provide substantial amounts of nutrients
+ focus on people during events so poorer recall
+ weighed food record = intrusive
Respect
+ need to be aware of occasions & only obtain essential data
What is bioavailability?
The proportion of a nutrient
in a food that is digested,
absorbed and utilised
How much non-haem iron is absorbed?
5-15%
How much iron is lost daily?
1mg/day (men)
2mg/day (women)
What are men & women’s iron requirements respectively?
~ 8mg/day; 18mg/day
Where is iron lost?
Epithelial cells: – Skin (~0.2mg) – Intestinal mucosal cells (~0.1mg) – Urinary tract cells (~0.1mg) • Fluids: – Blood (gut (~0.4mg), menstruation) – Bile (~0.2mg)
What is bioavailability influenced by?
- Chemical form of nutrient
- Food composition
- Meal composition
- person’s nutrient status
- Physiological status of person
- Amount consumed
Why do we measure bioavailability?
- Nutrient Reference Values set using %
absorption from typical diet - Identify & quantify new “enhancers” and
“inhibitors” of nutrient absorption - Compare efficacy of new supplements
- Develop algorithms to estimate absorption
What are isotopes?
same number of protons
different number of neutrons/ mass
What are radioisotopes?
Atoms with an unstable nucleus that emit alpha particles, beta particles & gamma rays during radioactive decay.
What are emissions of radioactive decay responsible for?
Ionising radiation –> removal of electrons from atoms, which damages tissues
What is the difference between alpha, beta and gamma particles?
Alpha particles (α) - Low penetrating power - Cause high ionisation Beta particles (β) - More penetrating than alpha - Not as ionising as alpha Gamma particles (γ) - High penetrating power - Causes least ionisation
What are radioisotopes used for?
• Balance studies admin dose – faecal (+ urine) losses • Whole body counting • Plasma appearance • Hb incorporation (for Fe)
What are advantages of radio isotopes?
- True tracers
- Often cheaper than stable isotopes
- Minimal sample preparation needed
What are the disadvantages of radio isotopes?
• Radiation dose (research doses ~ X-ray exam, or long-distance flight)
• Cannot be used with pregnant or lactating women, infants
or children
• Ethical approval only possible in certain countries
What are stable isotopes?
Naturally occurring isotopes that do not emit radiation
How are stable isotopes used?
• Balance studies
admin dose – faecal (+ urine) losses
• Plasma appearance
• Haemoglobin incorporation (for Fe)
What are the advantages of using stable isotopes?
+ No known health effects
• Can be used in any population
• Multiple isotopes (for Fe)
What are the disadvantages of using stable isotopes?
- Expensive – isotopes, equipment, time
- More sample preparation
- Need larger doses
- Only 1 stable isotope for iodine so can’t study absorption
What is the chemical balance equation to measure bioavailability?
Apparent Fe absorption = Fe intake – Faecal Fe
What are the advantages of using chemical balance equation?
- Whole diet not single meals
- No radiation
- Several nutrients at once
What are the disadvantages of using chemical balance equation?
• Large margin of error (can use faecal marker) • Nutrient retention may depend on status (some nutrients) • No correction for endogenous excretion (e.g. Zn)
What are algorithms?
Mathematical equations that Use intakes of selected enhancers and inhibitors to
estimate % of nutrient absorbed & assume a specific nutrient status
What are the advantages of using algorithms?
Quick + inexpensive
What are the disadvantages of using algorithms?
Underestimate absorption (Beard et al, 2007)
• Need food comp data for components not in FOODfiles
• Don’t account for interactions between abn modifiers
• Effects based on single meal not whole diet studies
Define EAR?
Estimate adequate requirements: meets the requirements of half the healthy population
Define RDI?
Recommended dietary intake: sufficient to meet 97-98% of the healthy population’s requirements
What is AI?
Adequate intake: assumed adequate intake of healthy population from observations
What is UL?
Upper limit: highest intake with no adverse heath effects
What are the uses of nutrient reference values?
Assessment and surveillance – Individuals and groups (L11-L12) • Planning diets – Individuals and groups • Inform policy • Education • Food labeling and marketing • Emergency food aid
What are the 3 main sets of recommendations?
• Nutrient Reference Values (NRVs) = Australia and New Zealand • Dietary Reference Intakes (DRIs) = United States and Canada • Dietary Reference Values (DRVs) = Europe
What is a physiological requirement?
The quantity of a nutrient needed by the
body to maintain a particular level of
function.
How do you determine physiological requirements?
+ Factorial estimation
• Depletion/repletion study
• Animal studies
What are physiological requirements influenced by?
• Physiological factors • Lifestyle factors • Biological & genetic factors • Environmental factors
How are EAR’s established?
- determine distribution + average physiological requirements (+ SD)
- Adjust for bioavailability & bioconversion
How is an RDI set?
RDI = EaR + 2SD
IF UNKNOWN ASSUME SD = 10
If there is no-observed-adverse effect level to determine a UL, what is used?
Lowest-observed-adverse-effect level with uncertainty factor
When is a larger uncertainty factor?
To animal data & when over-consumption has serious effects
Why is an uncertainty factory applied to UL or nutrient value?
• Limited data on distribution of physiological
requirements
• Data are mainly for young adult males
• Limited absorption data for different diet types
• Limited data on usual food intakes
• Limited data on interactions between nutrients
• Limited data on influence of host-related factors
What is the underlying assumptions when setting a nutrient reference value?
• Population is healthy • Nutrient intake is usual intake • Requirements for energy and other nutrients are being met • Nutrient requirements and intake are not correlated
What are 4 forms are nutritional assessment?
- Anthropometric assessment
- Dietary Assessment (nutrients & Dietary Practices)
- Biochemical Assessment
- Clinical assessment
What are appropriate uses of NRV’s?
Ear: used to examine probability adequeate
RDI: if this is usual intake -> level has low probability of inadequacy (qualitative)
AI: above AI = low probability of adequacy
UL: If above have high probability adverse effects
What is apparent adequacy?
estimate of one’s confidence is above or below own requirement
What is the quantitative approach to determining nutrient adequacy?
Calculate mean intake & find estimation of day-to-day variation
What reference standard should you use when determining nutrient adequacy?
EAR
How do you determine difference in intake vs requirements?
Difference = mean observed intake – median requirement
How do you determine SD of nutrient inadequacy?
SD of difference = (variance of distribution of reqs in groups + average variance in day-to-day intakes of nutrient/ no of days of intake))
How do you determine nutrient adequacy?
Difference/ Standard deviation of Difference
What is required to determine nutrient adequacy?
- Mean observed intake
- EAR
- Standard deviation of requirements
- Variance of requirements
- Standard deviation of day-to-day intakes
- Variance of day-to-day intakes
- No of days of observed intake
A value below the ___ cannot tell us anything the nutrient adequacy (only can determine adequacy above AI)
Adequate Intake
What is a qualitative approach to determining nutrient adequacy?
Assumes requirements & intakes are normally distributed
What is the qualitative approach to using EAR to determine nutrient adequacy?
+ Observed intake is less than EAR (50% probability need to increase)
+ If RDA is long term more than observed intake probs need to increase
+ If long term intake > RDA Probs adequate
What is the qualitative approach to using AI to determine nutrient adequacy?
If long term intake > AI = probably adequate (less cannot determine)
What is the qualitative approach to using UL to determine nutrient adequacy?
Observed intake > UL = risk over a large number of days (safe if not)
What are the limitations of determining nutrient adequacy using a qualitative approach?
+ Don’t have actual usual intake or actual requirements
+ Assume coefficient of variation = 10% for SD(requirement)
+ Assume SD (intake) is similar to pooled data
+ Assume no low energy reporting
+ Don’t have EAR for all nutrients