Indication
Estimated diaries are suitable for large-scale prospective studies, and for studies where detailed food and nutrient intakes are required at an individual level.
There is currently a debate on the relative merits of diet records versus FFQs for large-scale prospective studies investigating diet and disease relationships; an increasing school of thought suggests FFQs may not be sensitive enough to detect relationships between diet and disease (Thiebaut et al, 2008). The case for using diet diaries in longitudinal studies has recently been provided (Stephen 2007); the ever-increasing diversity and complexity of diets was one of the arguments for this position. Research investigating the link between breast cancer and dietary fat have shown mixed results (Knelt, 1990; Velie, 2000; Kim, 2006; Prentice, 2006; Sieri, 2008). It has been suggested that the differing findings may be due to the methods employed (Thiebaut et al, 2008). Two large cohorts have found a link between dietary fat and breast cancer using data from diet records; this link was not present using dietary data obtained from FFQs (Bingham et al, 2003; Freedman et al, 2006). However, the utility of FFQs is fiercely defended by other researchers, and in particular Walter Willett (Willett, 2001).
Estimated food diaries are a relatively expensive dietary assessment method, not in terms of administration to respondents but because of the extensive data processing required to translate the dietary intake information obtained into nutrient intakes. In spite of this, they are used in large population studies because of the quality of the data obtained. In 2007, a comparison study was undertaken in the UK comparing 4 day estimated diaries with four repeat 24- hour recalls in order to decide which method would replace the weighed seven-day diary previously used in the National Diet and Nutrition Survey. The estimated food diary was chosen on the basis of quantitative and qualitative outcomes; response rate, extent of misreporting and nutrient intakes were comparable between methods (Stephen et al, 2009). The diary does not require costly interview time compared to repeat 24- hour recalls. Estimated diaries have been used in the MRC National Survey of Health and Development (the 1946 British birth cohort), the EPIC Norfolk Cohort (Bingham 2001), the UK Woman’s Cohort Study which was undertaken in over 35,000 women (Cade et al, 2004) and in over 200,000 men in the ProtecT study (ProtecT Study website). The method has also been used in children in the Avon Longitudinal Study of Parents and Children (ALSPAC).