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REPORT OF THE WORKING GROUP ON MONITORING SCOTTISH DIETARY TARGETS

3. KEY METHODOLOGICAL ISSUES

3.1 Timescale

3.1.1 There is no single survey currently taking place in Scotland capable of measuring progress towards all the Scottish Dietary Targets. Therefore, use will be made of data available from several different surveys for monitoring progress towards the targets in 2005. Where robust data is unavailable, as is the case for the targets for sodium and for NME sugars in children, interim studies may need to be set up. The use of a more comprehensive dietary assessment tool should be considered for monitoring progress towards the Scottish Dietary Targets beyond 2005.

3.2 Sampling

3.2.1 The Scottish Dietary Targets are for the whole Scottish population (with the exception of the NME sugars target for children) and the targets will therefore be monitored at population level.

3.2.2 Recent policy has focused on inequalities and the Scottish Executive document 'Improving Health in Scotland: The Challenge' (Scottish Executive, 2003) sets out a commitment to tackling health inequalities. It is therefore envisaged that a monitoring tool should be capable of relating progress towards the targets to specific sub-groups of the population e.g. lower socio-economic groups, the elderly and minority ethnic groups.

3.2.3 The Scottish samples contained within existing UK nutritional surveys, such as the National Diet and Nutrition Surveys (NDNS) and the Expenditure and Food Survey (EFS), are currently too small to be representative of the Scottish population.

3.3 Survey Response Rates

3.3.1 The general decrease in response rates to surveys in the UK over recent years is problematic given that a high response rate is required to ensure a sample which is representative of the population. One potential way to improve response rates is to offer financial or other incentives, although it was recognised by the Working Group that there are possible ethical concerns regarding this approach.

3.3.2 Existing surveys that offer incentives to participants include the Low Income Diet and Nutrition Survey (LIDNS), where respondents are given 40, and the Expenditure and Food Survey (EFS) which pays adults 10 for completed record books and children 5. The incentive does not need to be high; Taylor Nelson Sofres (TNS) offers participants points for buying items from a brochure or record vouchers for taking part in market research, while respondents who complete the Survey for Lifestyles Attitude and Nutrition (SLAN) are entered into a prize draw. For more details of these surveys see Sections 4 and 5.

3.4 Dietary Survey Methodology

3.4.1 There are various methodologies available for assessing dietary intake including detailed individual weighed records collected over seven days or more, food frequency questionnaires (FFQ), multiple pass 24 hour recall, household survey methods and simple food lists. Each is designed for a different purpose and each has its specific advantages and disadvantages that need to be taken into account when choosing a methodology to monitor progress towards the Scottish Dietary Targets. The Working Group commissioned a review of these methodologies and this resulted in a briefing paper entitled 'A Short Review of Dietary Assessment Methods used in National and Scottish Research Studies'. Relevant sections from this review can be found in Appendix 5 and the full document is available from the FSA library, Aviation House, London or www.food.gov.uk.

3.4.2 Several of the dietary methodologies reviewed were considered to be insufficiently detailed to monitor progress towards the nutrient based targets but could, however, potentially be used for monitoring certain food based targets.

3.4.3 When measuring nutrient intake it is essential to collect information about food type and quantity in sufficient detail to translate food intake into nutrients using food composition tables.

3.4.4 In most dietary methodologies, with the exception of weighed intake, the quantity of food eaten is not directly measured. Portion sizes may be estimated in a number of ways including by the use of photographic atlases showing portion sizes of commonly eaten foods (e.g. Nelson M. et al., 1997), data from manufacturers, portion sizes collected from previous weighed food records and household measures. However, none of these are as accurate as a weighed intake measure.

3.4.5 Almost all dietary methodologies, including weighed intake, are prone to mis-reporting which occurs when the participants of a study change their eating behaviour as a consequence of being asked to record their dietary intake. This may take the form of under reporting food intake due to social bias, forgetting / being unaware of what has been eaten or substituting easier foods to record. Individuals may also over-report consumption of certain foods e.g. fruit and vegetables because they know they should eat them as part of a healthy balanced diet. A recent FSA funded study (Stubbs J et.al, 2003) has reported, in detail, the issues surrounding mis-reporting and its implications for dietary studies.

3.4.6 When measuring sodium intake, the conversion of foods to nutrients using food composition tables is deemed to be unacceptable due to the widely varying sodium content of convenience foods in particular. Instead, the preferred method is to estimate dietary intake indirectly by measuring the urinary output of sodium.

3.4.7 The Scottish Dietary Targets for total fat, saturated fat and NME sugars in children are expressed as percentage of total energy. Measurement of total dietary energy requires measuring the entire dietary intake. This is important to understand when choosing a methodology for monitoring progress towards these targets.

3.4.8 In short, there is no perfect way of assessing food and nutrient intake.

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