Estimated food diaries are detailed assessment methods that provide accurate estimates of energy intake and most nutrients, foods, and food groups. A comparison of methods in the UK arm of EPIC showed that a 7-day diary (estimated record) was in the closest agreement to 16 days of weighed intake and had the next highest correlation with biomarkers compared to a food frequency questionnaire and a 24-hour recall .
Individuals can record the time, location, and whether they consumed meals alone or with others for each eating occasion, providing information on eating patterns and the eating environment. The dietary outcomes which can be assessed by estimated food diaries are summarised in Table D.7.1. Recommendations are based upon multiple days of food diary entries rather than a single day in order to account for within-individual variation in diet over time.
Table D.7.1 Dietary outcomes assessed by estimated food diaries over multiple days.
|Possible to assess?
|Energy and nutrient intake of total diet
|Intake of specific nutrients or food
|Infrequently consumed foods
|Frequency of eating/meal occasions
|Adult report of diet at younger age
* possible when repeated measures were collected over time.
Estimated food diaries or records are a prospective dietary assessment method; an example is displayed in Figure D.7.1.
Figure D.7.1 Example of an estimated food diary used in a child population (enlarge).
Source: MRC Epidemiology Unit.
Estimated food diaries have been used successfully in many large-scale studies because of the quality and detail of the data obtained. They are suitable for studies where detailed food and nutrient intakes are required at an individual level. Due to its open ended nature, this method is useful to capture the diversity and complexity of diets. Estimated diaries have been used in:
However, the data entry requires substantial amounts of time, expertise in dietetics, as well as knowledge of a local food market, food culture, and possible dietary preferences. Without sufficient human resources, collecting food diaries would be risky to implement.
As a food diary has an open-ended format, its outputs can be diverse, including consumption of specific food groups, cooking at home, eating meals with family members or alone, use of table salt or dietary supplements, and whether breakfast, takeaway foods, or snacks between meals, were consumed. See characteristics of the outputs in the page of weighed food diaries.
Estimates of nutrient intakes follow a general procedure common with 24-hour recalls and food-frequency questionnaires. The following steps to estimate nutrient intakes are undertaken:
Nutrition experts may ask the question, “How much of vitamin A intake come from vegetable consumption in the population?” This can be easily calculated as the ratio of the total vitamin A intake from vegetables across all individuals to the total vitamin A intake from all foods across all individuals. This calculation is important to identify major food sources for a particular nutrient in a population.
Key characteristics are summarised in Table D.7.1.
Table D.7.1 Characteristics of estimated food diaries.
|Number of participants
|Up to ~5000
|Cost of development
|Cost of use
|Researcher burden of data collection
|Researcher burden of coding and data analysis
|Risk of reactivity bias
|Risk of recall bias
|Minimised if diary completed at time of consumption
|Risk of social desirability bias
|Risk of observer bias
|Participant literacy required
|Suitable for use in free living
|Requires individual portion size estimation
Considerations relating to the use of estimated food diaries for assessing diet in specific populations are described in Table D.7.2.
Table D.7.2 Diet assessment by estimated food diaries in different populations.
|Infancy and lactation
|Toddlers and young children
|May require proxy or adult assistance. A study in toddlers indicated no difference in energy intakes when an estimated diary was compared to a weighed diary .
|May require proxy depending on cognitive function. Larger-size diaries can be created for those who do not see well.
|Requires language/cultural specificity.
A method specific instrument library is being developed for this section. In the meantime, please refer to the overall instrument library page by clicking here to open in a new page.
In recording, taking photos of meals and voice-recording are useful. Photos taken can be digitalised into a volume and then to a weight with information on a density (gram/volume). Estimation of portion sizes can be aided by providing electronic photos that are readily searchable. The advantages include displaying portion sizes and reducing participants’ burden of documenting foods. Technology assistance is appealing, but computer literacy among participants should be sufficiently high and consistent in a study population.
The application of such technology assistance is under investigation. Ideally, the advanced approach should be compared to objective measures of dietary exposure.
Similarly to weighed food diaries, estimated food diaries are resource-intensive, requiring time and human resources to complete data entry and data standardization. Thus, food diaries (estimated or weighed) are practical and feasible to implement in a subset of a study population, although this still requires expert knowledge on data entry and further processing. Food diary data in a subset can then to be combined with dietary data from the entire study population derived using another dietary assessment method (e.g. multiple 24-h recalls, food frequency questionnaires). Unique statistical approaches are required to accurately merge multiple dietary datasets obtained from different methods .