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Nutrition lecture 4

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winniesmith2's version from 2017-10-26 14:55

Section 1

Question Answer
Why collect dietary intake data?1. National food and nutrition planning. 2. Toxicological aspects of food supply. 3. Studies with a nutritional focus
1. National food and nutrition planning-Assess adequacy of food supply -Improve nutritional quality of food supply -Set targets for food production -Monitor progress towards production targets -Assess how food is distributed within population -Use as a basis for developing food regulations -Develop guidelines for use in nutrition education
2. Toxicological aspects of food supply-Intake of food additives and contaminants -Intake of fortified foods
3. Studies with a nutritional focus-Assess dietary adequacy of groups or individuals -Evaluate nutritional impact of an intervention -Assess relationship between diet and disease
Choice of methodology- what do you need to consider1) The study (objective, level of precision required (i.e. quantitative vs. qualitative measures), what needs to be measured (past or current consumption) 2) The group(s) in question (individuals or populations) 3) The characteristics of the subjects (age, sex, level of literacy/education, socio-economic status, high income vs. low-and middle income countries) 4) The sample size 5) The resources available (money, time, staff)
What are the 3 types of food intake data 1) At national level: Availability to meet nutritional needs 2) At household level: Studies of food related expenditure 3) At household or individual level: Dietary surveys
What is food availability?the amount of food that is physically present in a country or area through all forms of domestic production, stocks, commercial imports and food aid.
What is a food balance sheet?is a key tool used to look at food availability at a national level. It describes all the factors that constitute total availability of food in a country in 12 months: -Published each year by FAO since 1961 -Data routinely collected in 176 countries -Data on 95 food products -Does not entail conducting special surveys. Not all the available food in a country is available for human consumption. Sheet incorporates estimates of 'losses' into the supple estimate to get availability of food for human consumption's.
food balance sheet equation Total production + imports + adjustment for storage levels – Exports – animal use – seeds – losses (storage, transport & processing)
What is the food gap is the difference between the estimated food available for human consumption and the consumption requirements. The estimate of a gap is an average across the population.
what is consumption requirements The food available for human consumption is compared to the food needed for that consumption (consumption requirements) over the selected period
FBS positives -Provide estimates of the quantity available for human consumption, for a country in a given time period - Give nutrient data expressed by food per capita and per year in energy (kcal) & macronutrients (proteins & lipids) -- Assess long-term trends -- Compare data across countries - -Provide global information on dietary patterns
FBS negatives - Does not account for seasonality - Does not account for local differences Does not measure actual energy intake Inaccuracy of data Assume that available food will be equally distributed to all people in a population (no distinction between food available to men and women, to adults and children, or to rich and poor)
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Section 2

Question Answer
What is the household budget survey -Surveys on family household food expenditure -Measures all food purchased and grown and received as gifts for the household -Provides an estimate of food and drink availability at household level
Advantages of household budget survey-Easy to set up -Allows an estimation of family’s consumption -Important source of info about the socio-economic factors that influence food choice
Disadvantages of household budget survey -Does not account for food waste (application of 10% coefficient in some countries). -Does not always account for food purchased and consumed outside home. -Does not give information on distribution within the family (except if data available to adjust for age & gender).
Retrospective methods Diet history -FFQ -24hr recall
prospective methods -Estimated intake -Weighed intake
What is weighted intake method-This method is widely used and gives an idea of actual intake. -Subjects (or investigator) weigh and record all foods and beverages immediately before consumption, and all plate waste (edible and inedible) at the end of the meal. -This method of recording is limited to subjects who are literate and numerate
Prospective methods; role of the interviewer (weighted)-Instructing the subject in how to use the scales and how to record food properly. -Checking that the subject is weighing/recording accurately. It should be emphasised that subjects should stick to their usual diet. -Motivating the subject to ensure correct weighing procedures and to give as much descriptive detail as possible.
What is estimated intake method -This method is widely used and gives an idea of actual intake. -The participant (or investigator) is asked to record in detail the foods and drinks consumed over a period of time usually prior to consumption. -Quantities consumed are estimated using household measures, food drawings and/or food models. -Assumes a certain literacy level.
Direct methods (quantifying intake)weighing, measuring volume
indirect methods (quantifying intake)Household measures: utensils and containers. andStandard food portion sizes: small, medium, large and, photo book, number of handfuls, food models
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Section 3

Question Answer
RECORDS COMBINED WITH DIRECT CHEMICAL ANALYSISFoods eaten are actually analysed for nutrient content. Chemical analysis is necessary when food composition tables are not available, or the food composition tables contain missing values for a particular nutrient.
1. Equivalent composite technique -Subject keeps a weighed food diary -For each day, the investigator will recreate the foods consumed and combine all the foods/beverages together (to create a food composite) -The investigator then takes samples (aliquots) for chemical analysis -All food is then analysed chemically in order to estimate the intake of nutrients.
2. Duplicate diet method -This technique is regarded as the most accurate -The subject is asked to make two of everything he eats and drinks (this method involves a lot of work for the subject!) -The subject then gives one to the researcher and eats the other one! -This process is usually combined with a weighed record
3. Aliquot method -This method involves the subject taking an aliquot of each food consumed immediately before consumption. -For example, the subject will weigh each food and then put 10% of the weight into a labelled container (which contains preservatives). -Subsequently, the combined aliquots are analysed for nutrient content.
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Section 4

Question Answer
Food records summary-Food records, or diaries, administered to subjects for completion in their own time. -Subjects keep records for extended periods of time (usually 3–7 days): +Record all foods and beverages consumed at the time they are consumed +Longer records may be desirable for some micronutrients -Portion sizes can be recorded in a number of different ways: +Estimated intake in simple household measures (e.g., 2 tablespoons of rice, 1 cup of sugar) +Estimated intake through comparison to a pictorial atlas of portion sizes +Weighing food on standardized scales, taking into account any wastage (a weighed food record)
Inaccuracies in food records Inaccuracies in estimates of portion sizes are a major problem associated with food record methods- approach should be chosen to best serve the purpose of the dietary survey: -Surveys of small groups of well-motivated people in a metabolic unit- weighed record method -Larger survey of free-living individuals – estimated food record
Positives and negatives of food records.Subject records as they eat removing effects of recall. Act of recording can make something simple like making a sandwich into a chore. If recipes are not provided then the accuracy of data will be undermined. Subject may only record what he/she wants the researcher to see…
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Section 5

Question Answer
24HR recall -Ideal method for examining individual nutrient intakes in a clinical setting. -This method is the most widely used to obtain quantitative recall data. -Trained interviewer to interview patient or research subject to elicit detailed information on all food and drink consumed over a recent period of time
What needs to be recorded in 24hr recall -All food and beverages consumed during that period -Descriptions of recipes, cooking methods, portion sizes, use of condiments -Intakes over the preceding 24 h, but in some cases may look at 48-h or 72-h periods.
24 hr recall - how -Information coded for detailed analysis of energy and nutrient intakes using appropriate nutritional analysis software or food tables. -Quantities consumed are estimated using household measures, food drawings and/or food models. -Use of photographic food atlases showing portion sizes for commonly consumed foods can enhance the quality of data. -This method is appropriate for large scale surveys. -High response rate when using this method in comparison to prospective methods
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Section 6

Question Answer
Food frequency questionnaire -A FFQ estimates habitual intake of foods, or groups of foods. -A FFQ collects information on the frequency and amount of consumption of specific items of food and drink. -Participants are given a list of items with a selection of options for reporting the frequency of consumption of each food item (daily, weekly, monthly, per year or never). -Mostly generate data on foods rather than nutrients. Also include info on the quantity consumed, which enables nutrient estimation using food analysis software- appropriate for large scale surveys
Semi-quantitative FFQs will estimate quantities using standard portion sizes (small, medium or large).
Quantitative FFQs will estimate quantities using household measures, food drawings and/or food models.
FFQ can vary in length and complexity -Longer FFQ give comprehensive coverage of the dietary patterns of a subject . -Shorter FFQ may be focused upon a particular food group or the main sources of a specific type of nutrient.
What does FFQ do Provides an estimate of habitual intake over a period of months or years, as opposed to the snapshot obtained by looking at a food record
What does FFQ need to be -Must be valid for the population to be studiedRange of foods consumed varies with age, ethnicity, religious beliefs -New FFQ undergo extensive validation ; Compare food frequency data with dietary recalls and/or weighed food records in the same individuals
Diet history -This method attempts to estimate the usual food intake and meal pattern of individuals over a relatively long period of time. It provides qualitative information on usual food intake. -Three components: +Interview about the usual overall eating pattern of the subject at mealtimes and between meals +Cross check: questionnaire on the frequency of consumption of specific items +Subjects record their food intake at home for three days
diet history pros: provides good picture of usual intake
diet history cons expensive, labour intensive and depends on skill of interviewer
watch learn recording /use watsapp photoswrite down strengths and weaknesses for each dietary assessment method
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Section 7

Question Answer
what are the 4 Dietary errors1. Error terminology 2. Reproducibility in dietary assessment methods 3. Validity in dietary assessment methods 4. Sources of measurement error
What is an errorthe difference between the true value of a parameter such as intake and the value obtained from a measure such as reported intake.
What are the 2 types of errorrandom and systematic errors
What is a random error It is an unpredictable source of error that contributes to variability. These random errors may be for various reasons, e.g. food omitted, coding errors etc. On average, they cancel each other out, but they affect the precision of the estimated intake.
What is a systematic error: A source of error in which measurements consistently depart from the true value in the same direction (i.e. the tendency of a measurement to produce an over- or under-estimation of what the method is intended to measure). Such a systematic error causes a bias in the estimation.
What is reproducibility the extent to which a method produces the same results when repeatedly applied in the same situation. The smaller the within-person variability (i.e. the variability in nutrient intake from day to day), the greater the reproducibility. Synonyms for reproducibility are: repeatability, reliability, replicability and precision Reproducibility is affected by random error
What is validity/accuracythe extent to which the method measures what it is intended to measure. Both systematic and random error detract from the accuracy of the measurement.
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Section 8

Question Answer
Non response bias Random sample of subjects not representative of the studied population
Respondent bias Systematic over-reporting or under-reporting of foods consumed; social desirability and approval biases
Interviewer biases When different interviewers probe for information to varying degrees, omit questions or record responses of subjects incorrectly. Biases could also be associated with the interview setting (distractions, confidentiality, relationship between the interviewer and interviewee)
Respondent memory lapses Unintentional omission or addition of foods in recall methods
Incorrect estimation of portion sizeRespondents failing to quantify accurately the amount of food consumed or from misconceptions of an average portion size
Coding errors Can arise when portion size estimates are converted from household measures into grams and when food items are assigned codes
Food composition tables Errors inherent in food composition tables
more info on each slide 51-58
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