Lecture 5 Measures of dietary exposure in individuals

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  • Measuring food intake is one of the most difficult tasks undertaken by health professionals because:Food supply is extremely variedIndividuals eat widely varying amounts and combinations from day to dayVariations exist in recipes and nutrient content of different versions of the same foodTask of recording foods in detail is time consuming and requires a lot of co-operation from respondents
  • potential to provide quantitatively accurate information on food consumed during recording period. historically viewed as the ‘gold standard’.omission of foods eaten less likely than recall methodsmore accurate information on portion sizes as most not estimatedgives information re meal patterns and specific type so foods eaten
  • respondents need to be motivated, numerate and literate respondent burden high, especially for 7 day record? change intake to simplify the weighing procedure or to impress investigatorsbias in representativeness of respondents who successfully undertake the rigours of the 7 day record
  • Gold standard’ status now questioned; serious systematic under reporting has been documented.
  • respondent burden small and compliance generally highmethod quick, relatively inexpensive, useful for subjects with low literacy? greater representativeness as burden is small and suitable for wider cross section of populationdoes not change dietary habits as consumption has already occurredcoding easier due to standardisation and certain amount of precoding can be done, ? direct entry into computersome information on meal patterns and intake of specific foods eg fruit and vegetables
  • Widely used in large scale epidemiological studiesGenerally not adequate to estimate absolute intake, better suited to comparisons and ranking
  • Assessment of usual intake over a specific time period not widely used although some increased interest latelyuseful for assessing energy and macronutrient intake of groups and to rank individualsmainly clinical use
  • dependant on memory and ability to give historybias towards those with regular meal intake and patternmay exaggerate the regularity of meals and underestimate intake of snack foodsno indication of day to day variability in intakerequires highly trained and skilled staff - high risk of interviewer biasmore likely to recall immediate past than period of interest
  • Variation in diet - natural phenomenon not error, but must be accounted for in design and choice of methodsinter-subject: between persons intra-subject: within subjects over time ie from day to day, season to season, year to year. degree of variation depends on the nutrient. Nutrients found in wide range of foods have lower variation than nutrients concentrated in a few specific foods eg carotene/Vitamin A.some nutrients within-person >>between person - difficult to detect difference between groups/individuals
  • Validity: For the study subjects; internal validityfor the relevant others outside the study - external validity
  • Lecture 5 Measures of dietary exposure in individuals

    1. 1. XNN001 Population nutrition and physical activity assessment
    2. 2.  Usual intake more important than one day snapshot  Methods of measuring dietary intake include ◦ Diet History ◦ 24hr recall ◦ Food frequency questionnaire ◦ Food diaries ◦ Duplicate meals  Used to investigate quality of diet (core-foods) and energy intake
    3. 3.  Present/prospective ◦ Diaries  Household measures  package weights  numbers of items  size of items  Weights ◦ Chemical analysis  Duplicate meals  Past/retrospective ◦ Actual  24-hour recall  Food Frequency Questionnaires ◦ Usual  Dietary Histories
    4. 4. Prospective (current) Retrospective(past) • Actual • 24-hour recall • Food Frequency Questionnaires • Usual • Dietary Histories •Food diaries • Household measures or weighed •Chemical analysis •Duplicate meals
    5. 5.  Current diet: Heisenberg uncertainty principle: as soon as you stop something to measure it you change the behaviour  Past diet: relies on memory, conceptual and cognitive ability and honesty on part of respondents  No direct measure of what people eat will provide a true picture of their dietary habits  Task is to understand and define the errors, try to minimise, manage statistically and incorporate in interpretation of results. 5
    6. 6.  Is information needed about foods, nutrients, other food constituents, dietary behaviours (eg eating meals)?  Is the average intake of a group required? eg. do Australian Vietnamese babies have lower iron intakes than Caucasian Australian babies  Is the average intake of each individual needed ? eg is iron intake of Australian Vietnamese babies related to the prevalence of anaemia in this group. 6
    7. 7.  Using household measures ◦ Set time period for recording (minimum 3 days) ◦ Record all food consumed & drink over there days in diary ◦ Include a non-working day  Using weights ◦ Similar recording to above but use a set procedure for weighing using scales & measuring utensils
    8. 8.  Requires the participant to record food and drink eaten and estimate the amount
    9. 9.  supplement use recorded  number of days varies, traditionally 7, 3 or 4 consecutive days, including a weekend day for 3/4 day records  number of days required can be determined statistically and depends on the nutrient of interest, objective of the study etc 9
    10. 10.  Potential to provide quantitatively accurate information on food consumed during recording period  ‘Gold-standard’  Less likely for foods to be omitted  Accuracy of portion sizes  Information RE meal patterns and specific foods 10
    11. 11.  Motivation and high levels of literacy required  High respondent burden  Change in intake (result of monitoring)  Bias in representativeness of respondents 11
    12. 12.  Gold standard’ status now questioned (systematic under reporting)  major issue is how representative the recording period is of ‘usual’ diet, apart from the issues of reporting errors. ie natural variation in diet.  high coding burden, especially in large studies 12
    13. 13.  Observed or plate waste method ◦ respondent researcher burden ◦ under reporting  Estimated portions ◦ hh measures, plate pictures, food models, photos – mobile phones 13
    14. 14.  Collection of an identical meal/food from client for analysis ◦ useful for analysing food composition  Limitations ◦ expensive & time consuming ◦ impractical outside confined setting
    15. 15.  Ask individual to remember what food & drinks they have consumed in previous 24 hours or day ◦ usually performed by trained interviewer Let’s try a 24-hour recall 1. Write down on a piece of paper what you have eaten in the last 24 hours 2. Do you think there is sufficient detail for you to analyse it in detail? 3. Do you think you have been completely honest? 4. Could you remember exactly? 5. Could you estimate quantities accurately? 6. Do you think this record is typical for you?
    16. 16.  Low respondent burden  Quick, inexpensive  Low levels of literacy required  Potential for greater representativeness  Does not change dietary habits as retrospective  Coding easier  Provide some information on meal patterns/ intake of specific foods 16
    17. 17.  relies on memory  portion estimation  relies on interviewer skill, potential for observer bias  can only provide group means, assess proportion of population with adequate/inadequate intakes  does not provide data on usual intake of individual, no day to day variation – repeat recall 10%  multiple 24h recalls have been used to provide usual intake of individuals. Criteria used to decide no of days of records apply non-consecutive days, no subject notice 17
    18. 18.  Qualitative & semi-quantitative survey of: ◦ how often foods are eaten +/- how much ◦ usually self administered, can be interview ◦ general or specific FFQ  Developed to be used for large groups Information about usual food consumption patterns
    19. 19.  3 sections: (i) food list (ii) frequency of use categories (iii) estimates of quantities usually consumed  May be administered by self (post), interviewer and now often optically scannable 20
    20. 20.  Estimates usual intake of foods  Rank individuals according to their usual intake of foods or groups of foods (and nutrient intake if portion sizes included)  Widely used  Generally not adequate to estimate absolute intake  Can behave unpredictably in subpopulations, must be validated for study population 21
    21. 21.  Easy and cheap to self administer  Avoids observer bias  Suitable for geographically widespread sample as can be done by telephone or post  Small burden for respondent 22
    22. 22.  Cannot use FFQ designed in US here, even UK to here difficult, adult FFQ cannot be used for children or adolescents  No information on food intake and meal patterns;? use supplementary questions 23
    23. 23.  Amount of work required to develop and validate  Quantification of intake not as accurate as recalls/records.  Errors  incomplete listing of foods  errors in frequency estimation  errors in portion size estimation  Memory and period of recall required has major issues eg 12 months, three months etc. 24
    24. 24.  Seasonal variation difficult to capture eg mangoes  Tend to overestimate, particularly fruit and vegetable intake  Cognitive difficulties with reporting foods eaten alone and in combination, risk of double counting 25
    25. 25.  Foods grouped (eg beefburgers, steak, steak pie) - assumptions made on contribution each food makes to the overall reported frequency and portion size  FFQ designed for one ethnic group are unlikely to be suitable to others due to major differences in food types, recipes, food combinations & frequency 26
    26. 26.  Requires nutritionist to interview participant and to record detail and estimate the quantities of usual/ typical intake Original adaptation - 3 components 1. a usual 24-hour recall usual takes away atypical errors food amounts enhanced by using food models 2. a checklist 3. a short (3 days) diary
    27. 27.  Original methodology more commonly now adapted - Multiple variations  An investigation of habitual intake over a specified period of time – usually 1 mo to 1 yr  24 hour recall + variations  Details on types (e.g. low fat), quantities, brands)  Indicates patterns of eating  Able to estimate energy, macro & micro nutrients  Able to estimate food groups  Can be targeted to particular nutrients e.g. carbohydrate in diabetes  Administered by a trained health professional
    28. 28.  a usual 24-hour recall ◦ would you normally consume breakfast? ◦ what would you normally have? ◦ what type of bread would that usually be? ◦ etc
    29. 29. CHECKLIST  bread, cereal, rice, pasta, biscuits, crackers  vegies, fruit, juices  meat, offal, poultry, fish, seafood, eggs, legumes  milk, cheese, yoghurt, ice cream, milk drinks  butter, marg, oils, dressings Miscellaneous:  soups, gravies, sauces, pickles, sugar, jam, honey, p/butter, vegemite  cakes, desserts, lollies, chocolates  snack foods, nuts, chips, munchies  soft drinks, cordials, water  alcohol  weekends, take-away, eating out  salt  supplements (vit/min/fibre)  cooking methods etc
    30. 30. DietHistoryExample
    31. 31.  honesty, memory & frankness of client  need highly skilled interviewer  expensive & time consuming  may underestimate intake Most useful information for assessment
    32. 32.  Depends on memory  Bias towards those with regular meal intake and pattern  Exaggeration of meal regularity  Underestimation of snacks  No indication of day to day variability  Requires highly trained and skilled staff - high risk of interviewer bias  More likely to recall immediate past than period of interest 33
    33. 33.  Single interview gives detailed information on meal patterns, food consumption, usual nutrient intake  Information on usual intake over long periods can theoretically be obtained  Particular attention can be given to nutrients of interest and goods/ drinks that are often under reported eg alcohol, confectionary  Detailed food preparation can be obtained  Seasonal variation can be assessed 34
    34. 34.  duplicate portion methods  PETRA (Portable Electronic Tape Recorded Automatic) Scales - linked scales & tape recorder  photographic methods - atlas of photographed food potions  video recording of meals – use of mobile phones  computer assisted automated diet histories/ 24 hour recalls 35
    35. 35. 39
    36. 36. Respondent bias  inaccurately report income and age  over report consumption of ‘good foods’  under report ‘bad’ foods - alcohol, snack foods, confectionary etc  overweight respondents may under report total food intake 40
    37. 37.  Respondent memory lapses  Incorrect estimation of portion size ◦ concept of ‘average’ serving size differs ◦ weighed vs estimated does not seem to introduce bias  Daily variation in one respect not an error but does introduce misclassification 41
    38. 38. Supplement usage  fail to record gives underestimation of nutrient intake Frequency food consumption  FFQ tend to overestimate intake, especially fruit and veges  No. of food items can have an effect, shorter list tends to increase bias associated with estimation of single food items 42
    39. 39.  Certain groups, eg overweight, systematically under report their habitual food intake; diabetics tend to report prescribed diet  Recently identified problem that has called into question the ‘gold standard status’ of the 7 day weighed food record.  Must demonstrate if present/not  Must identify under-reporters for analysis  ? Exclude, depends on aims 43
    40. 40. Day of the week affect  significant week/weekend day differences for some foods and nutrients  likely to be culturally and economically significant and change over time  need to proportionately represent weekend days in design 44
    41. 41. Seasonal effects  can be very specific especially in developing countries and poor communities  variation tends to be greater for foods than nutrients  some micronutrients significantly effected by fruit and vegetable consumption  survey across seasons if possible 45
    42. 42.  Essential to help understand the relationship between what we have measured and the ‘truth’  Describe and quantify error as far as possible to enable consideration in analysis interpretation of results  To ensure the tool will allow us to detect the diet disease relationship should it exist  Inadequate attention to validation results in wasted resources and failure to detect true relationships between diet and disease` 46
    43. 43. Reliability  reproducibility; repeatability  if we did it again would we get the same answer  measure reliable but not valid; if valid must be reliable Validity: are our findings true?  requires a true external reference measure or standard 47
    44. 44.  Not possible to have absolute direct measure of dietary intake, ie errors in all methods  aim to establish ‘relative validity’  compare test method with reference method  does not necessarily indicate method valid, may indicate both methods have the same errors  Relative validity major issue in nutritional epi 48
    45. 45.  validity and reproducibility of reference method should be high  7 day record has been the classical reference method - not error free  errors should be independent eg recall method validated by prospective method eg FFQ against Diet history -can reflect same exposure period but both rely on portion size and frequency estimations and recall skills 49

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