REPORT OF THE WORKING GROUP ON MONITORING SCOTTISH DIETARY TARGETS
Appendix 5: Briefing Paper on Dietary Assessment Methods
A.5.1 The Working Group on Monitoring Scottish Dietary Targets commissioned a review of the methodologies used in diet research surveys. The report was complied by Dr Wendy Wrieden (University of Dundee), Mrs Heather Peace (University of Aberdeen), Mrs Julie Armstrong (Glasgow Caledonian University) and Ms. Karen Barton (University of Dundee). The relevant sections are included here and the full report is available from the FSA library, Aviation House, London.
A Short Review of Dietary Assessment Methods Used in National and Scottish Research Studies
The appropriate tool for dietary assessment will depend on the purpose for which it is needed. The purpose may be to measure nutrients, foods or eating habits. To monitor the Scottish Dietary Targets it is necessary to measure both nutrient and food intake although exploration of eating habits may be helpful to understand the process of achieving dietary change. Many different methods have been developed for the purpose of assessing dietary intake. These range from detailed individual weighed records collected over a period of 7 days or more to food frequency questionnaires, household survey methods and simple food lists. Each has merits, associated errors and practical difficulties to be considered when choosing one method above another. Several of the dietary assessment tools described do not collect sufficient detail to assess nutrient intake (and thus progress towards nutrient based targets) but may be capable of assessing and estimating intake of specific foods (and thus some of the food-based targets).
1. Methods designed to measure food and/or nutrient intakes
In general the procedure for measuring energy and nutrient intake involves:
I. A report of all food consumed by an individual
II. Identification of the foods such that an appropriate item can be chosen from standard food tables. In detailed studies a duplicate portion of the food may be chemically analysed to find out the nutrient content
III. Quantification of the portion size of each food item
IV. Determination of the frequency with which each food is eaten
V. Calculation of the nutrient intake (portion size (g) x frequency x the nutrient content per g).
(Rutishauser and Black, 2002)
To measure food intake alone it is possible to miss out steps (II) and (V). Indeed if we are only interested in the intake of certain foods it may not be necessary to have a report of all food consumed. However quantification of the amounts eaten is necessary if comparison with a food based target or recommendation is required e.g. the 400g of fruit and vegetables in the Scottish Diet Action Plan Targets.
1.1 Weighed Food Records
This involves an individual or an investigator weighing each and every item of food and drink prior to consumption. A detailed description of the food and its weight is recorded in a specially designed booklet. Usually a space is left to record any leftovers so that the precise weight of food eaten can be calculated. Weighed records can be kept for 3,4,5 or 7 days. The 7 day weighed record has often been taken as the 'gold standard' against which less detailed and demanding methods can be compared. It is now recognised that the method also has limitations and it is necessary to use physiological and biochemical methods (e.g. the use of doubly labelled water which measures energy expenditure- energy intakes less than the energy expenditure are likely to be invalid) to check that any method of measuring food intake is measuring what it is supposed to measure. Weighed food records of 7 days or 4 days were used in the NDNS programme.
1.2 Estimated Food Records
This is similar to the weighed food record method except that the quantification of the foods and drink is estimated rather than weighed. This estimation is carried out using
The investigator converts these estimates into weights that can then be used to calculate food and nutrient intake. The EPIC study used a 7 day estimated food diary with portion sizes being recorded using household measures and colour photographs.
1.3 24 Hour Recall
This method requires a trained interviewer to ask the respondent to remember in detail all the food and drink they consumed during a period of time in the recent past (often the previous 24 hours). As a retrospective method it relies on an accurate memory of intake, reliability of the respondent not to under / misreport, and an ability to estimate portion size. This may be helped by the interviewer prompting the respondent to remember eating and drinking episodes by time periods (e.g. starting on awakening), or linking to day time activities (e.g. arriving at work). In addition the interviewer may use prompts to assist the respondent to estimate portion sizes of the items consumed. The interviewer records the dietary information which at the end is checked for omission / errors and is then coded for analysis. The primary limitation of this method is that recording consumption for a single day is seldom representative of a person's usual intake due to day-to-day variation. An extended and more accurate version of this method is the Multiple Pass 24-hour recall.
Estimation of portion sizes
Single observation provides poor measure of individual intake
Bias in recording "good/bad" foods
1.4 Multiple Pass Recall
This method was developed in the United States of America (USA) to assess diet and nutrition in large population studies; 1999-2000 National Health and Nutrition Examination Study (NHANES) and the Continuing Survey of Food Intakes by Individuals (CSFII). In the USA it has been used to assess the diets of children and adults. The diet is assessed over a period of three to five days during which the respondent is asked to recall and describe all food and drinks consumed in the 24 hour prior to the interview. Interviews can be a combination of face to face and telephone. The multiple pass refers to the steps involved during interview to allow revisiting and checking of dietary information: in the first pass, a quick list of foods consumed is obtained; in the second pass, information about the meal / snacks consumed (including time and place) are recorded. The third pass prompts for foods that may have been forgotten. Finally a review of the record and further details of foods consumed and portion sizes is completed. The method has been modified over the past five year with the specific aim to minimise under-reporting and the burden on respondents.
The method was adapted and validated for measuring energy intake in a Scottish sample of pre-school children. In the validation study (Reilly et al., 2001) of 41 pre-school children aged 3-4 years (23 boys, 18 girls) recall interviews with parents were used to assess diet over 3 consecutive days (two weekdays, one weekend) using both face to face and telephone interviews. For the first recall interview (face to face) the time averaged 15 - 20 minutes. For the second and third recall interview (telephone) it was < 10 minutes. Portion sizes were estimates from household measures and published food portions. The group estimate of energy intake was significantly (p <0.01) greater than energy expenditure (measured using doubly-labelled water) by 11%. The method was found to be quick for investigators and respondents and well tolerated. The bias in estimating energy intake may be reduced by using children's portion sizes to estimate food weights.
Data entry can be labour intensive. The multiple pass methodology is currently being used in the UK wide LIDNS.
Improved precision compared with 24 hour recall
Low respondent burden
Suitable for large scale surveys
Can be administered by telephone
1.5 FFQs and semi-quantitative FFQs
At its simplest, the FFQ consists of a list of foods and a selection of options relating to the frequency of consumption of each of the foods listed (e.g. times per day, daily, weekly, monthly). FFQs are designed to collect dietary information from large numbers of individuals (100 individuals or more) and are normally self-administered, though interviewer administered and telephone interview are possible modifications (Haraldsdottir et al., 2001). FFQs normally ask about intake within a given time frame (e.g. in the past 2-3 months, 1 year or longer) and therefore aim to capture habitual intake. The length of the food list can vary depending on the nutrients or foods of interest. If a range of different nutrients and energy values are required, the list of foods may be upwards of 150 foods whereas the Ca/VitDFFQ described below contains just 11 food items since the major sources of the nutrients of interest are found in relatively few food types.
Many FFQs also attempt to collect information about portion size in addition to frequency of consumption. These may be referred to as semi-quantitative FFQs. Where portion size information is not obtained standard food portion sizes (MAFF, 1993) are often used to calculate nutrient intakes as is done for many of the FFQs based on the Caerphilly questionnaire (Yarnell et al., 1983). Although there are difficulties implicit in calculating the absolute nutrient intake of individuals from food frequency questionnaires, they are useful in gathering information on groups of individuals as well as for looking at habitual intake of a range of foods.
Food lists are a type of FFQ used in the SHS and the various Health and Lifestyle Surveys carried out by individual health boards. These are brief questionnaires designed to measure specific dietary behaviours (Cade et al., 2002). It is not possible to measure nutrient intake from these questionnaires and depending on the foods and frequencies specified it may be difficult to look at adherence to specific dietary targets. However, Lean et al., (2003) described how the dietary questions from the SHS could be used for limited monitoring of the Scottish Dietary Targets. They measured relative validity using the MONICA FFQ and found that the there was a bias to underreporting fruit and vegetables and starchy foods, but not fish using the SHS questionnaire.
Estimation of portion sizes (though use of food photographs may improve precision)
Possible over-reporting of 'healthy' foods (e.g. fruit and vegetables)
Requires to be validated in relation to reference method
1.6 Household Food Surveys
A number of surveys aim to collect information about dietary intake at the household level. The most notable of these, in terms of monitoring long term UK dietary intake, is the EFS and its predecessor the NFS, which together provide information on UK food expenditure and food and nutrient intake trends over a period of more than 40 years. Some market research surveys relating to food purchases trends are conducted at the household level.
Recently, a feasibility study has highlighted the potential of utilising large quantities of readily available data generated from supermarket checkouts in dietary surveys (Ransley et al., 2001). The association between fat and energy measured by supermarket till receipts and 4 day weighed records was found to be strong. Till receipts are also collected as part of the new EFS.
1.7 Methods measuring nutritional status (non biological)
Nutritional assessment tools are frequently used in clinical practice but few have been developed scientifically for use in public health studies. The Nutrition Assessment Questionnaire was developed to identify individuals at risk of marginal and poor micronutrient status (as opposed to dietary intake) living within the community.
References for Extract from A Short Review of Dietary Assessment Methods Used in National and Scottish Research Studies
Cade J, Thompson R, Burley V, Warm D (2002) Development, validation and utilization of food-frequency questionnaires - review. Public Health Nutrition5 (4), 567-587
Haraldsottir J, Holm L, Astrup AV, Halkjoer J, Stender S (2001) Monitoring of dietary changes by telephone interviews: results from Denmark. Public Health Nutrition; 4(6),1287-1295.
Lean, MEJ, Anderson,AS, Morrison,C. Currall,J (2003) Evaluation of a Dietary Targets Monitor. European Journal of Clinical Nutrition: 57 (5), 667-673
MAFF (1993), Food Portion Sizes . Second Edition. London. HMSO.
Ransley JK, Donneley JK, Khara TN, Botham H, Arnot H, Greenwood DC, Cade JE (2001): The use of supermarket till receipts to determine the fat and energy intake in a UK population. Public Health Nutrition;4 (6), 1279-1286.
Reilly, J, Montgomery C, Jackson D, MacRitchie & Armstrong J (2001) Energy intake by multiple pass 24 h recall and total energy expenditure a comparison in a representative sample of 3-4 year olds. Br. J. Nutr. 86, 601-605.
Rutishauser IHE and Black AE (2002) Chapter 10, p 225-248 of Introduction to Human Nutrition, edited by Gibney M,Vorster H and Kok FJ. The Nutrition Society Textbook Series, Blackwell Publishing.Oxford.
Yarnell JWG, Fehily AM, Milbank JE, Sweetnam PM, Walker CL (1983) A short dietary questionnaire for use in an epidemiological survey: Comparison with weighed dietary records. Human Nutrition: Applied Nutrition 1983;37A:103-112.
Copies can be obtained from:
The Food Standards Agency Scotland
6 th Floor
St Magnus House
25 Guild Street
Tel: 01224 285100
Fax: 01224 285110
Website: www.food.gov.uk/scotland or www.scotland.gov.uk/topics/health/health