Dietary assessment tools (DATs)

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In epidemiological research, diet is often assessed using dietary assessment tools (DATs). The aims of most DATs are to collect an accurate record of habitual food and nutrient intake for a group of individuals. This can be extremely difficult, particularly due to the significant variation in dietary intake within individuals. There has been extensive work in developing DATs. There are two online resources, both supported by the Medical Research Council, which give a comprehensive overview of DATs:

Nutritools (opens new tab) developed by the DIET@NET partnership
DAPA Measurement Toolkit (opens new tab) developed by the University of Cambridge (also supported by the NHS, European Union and InterConnect Project)

Each DAT has specific strengths and weakness and the one used should be suitable for the research question, overall study design and population of interest. The reliability and validity of these tools have been discussed in Willett 2013 [6] and guidance on use of DATs is given in the online resources listed above. The tables below (information adapted from Willett and Nutritools.org [6, 15]) give a brief overview of the main DATs used in the original CLOSER partner studies.

Click below for an introduction to each of these DATs:

24-hour recall
Food frequency questionnaires (FFQ)
Diet diaries

24-hour recall

Retrospective in-depth interview capturing everything the participant had to eat or drink over the past 24-hour period. This can be administered in person over the phone or online. There is opportunity to probe for additional foods and food preparation methods and to use prompts and aids for portion size estimation.

Strengths	Weaknesses
Can provide detailed information as it is open ended. This provides good estimates of short-term intake of absolute intakes (good for when comparing when specific dietary recommendations)	Does not capture irregularly consumed foods
Provides data that can be analysed in different ways	Relies on good participant episodic memory
Can provide some contextual information depending on design e.g. who else was present when eating	Relies on recalled and estimated portion sizes
Useful for capturing intake in culturally diverse contexts	A single day is not representative of usual individual intake due to day-to-day variability (use of multiple 24-hour recalls over a sufficient number of non-consecutive days and seasons can overcome this)
Moderate participant burden and high compliance (depending on number of days)	A single day can under/over-estimate habitual intakes of certain nutrients from irregularly consumed foods
	When used in epidemiological associations, estimates may be attenuated as day-to-day variation is not accounted for
	Moderate to high researcher burden due to coding
	Can be expensive and time-consuming to code
	Forgotten items are common (exclusions) and intrusions (items included but were not consumed) also occur

Food frequency questionnaires (FFQ)

Retrospective method where the participant reports frequency of usual consumption of a specific food/food group over a pre-defined period of time. Questions on quantity can also be included (semi-quantitative FFQ or fully-quantitative FFQ). The number of food/drink items included in the FFQ vary and can be long (comprehensive FFQ) or short. It can be administered in person or over the phone or self-completed on paper or online.

Strengths	Weaknesses
Can capture usual intake retrospectively	Precision of intake estimates is reduced
Can capture foods consumed irregularly	Information is limited to the food/food groups included in the food list; this can decrease cross-cohort comparison especially when diverse cultures are being compared
Can rank participants into intake levels	Short FFQs may not be reliable for total diet/nutrient intakes
If a long FFQ is used and portion size estimated, usual dietary intake and total nutrient intake can be estimated	Relies on good participant generic memory and literacy and numerical skills
Low participant burden so useful in large population studies	Needs careful design and validation in the population of interest as prone to misreporting
Low researcher burden as coding is less intensive than recall or diet diaries

Diet diaries

Prospective methods in which the participant records everything consumed over a number of days. It is best when these days include a mixture of weekend and weekdays. The amount of food/drink consumed can be estimated using household measures or weighed in the home. These diaries can include prompts and photographs to aid description of portion sizes and can be completed in paper format or online.

Strengths	Weaknesses
Provides detailed information on short-term intake leading to good estimates of total dietary/nutrient intake	Not suitable for retrospective study
Provides data that can be analysed in different ways	Does not capture irregularly consumed foods
Can provide some contextual information depending on design e.g. who else was present when eating	Potential for reactivity (changes of usual food choice) as number of days increases
Limits reliance on memory	Good literacy and numeracy skills needed
	Relies on participants to estimate portion sizes
	High participant burden, particularly as the number of days increases
	High researcher burden as coding can be complicated

Explore additional background detail:

Learn more about the individual studies covered by this guide and their dietary measurements:

Learn about harmonisation in the context of dietary data:

Discussion & illustration of dietary data harmonisation

Further information:

This page is part of the CLOSER resource: ‘A guide to the dietary data in eight CLOSER studies’.