Dietary assessment - Estimated food diary
Estimated food diaries or records are a prospective dietary assessment method which provide detailed data on food and nutrient intakes. Individuals record details of foods and beverages consumed at the time of consumption. Brand names, cooking and preparation methods should be provided by respondents. Portion sizes should be estimated and photographs, household measures or natural unit sizes (e.g. slices of bread) are commonly used for this. Foods can also be weighed and recorded if an individual chooses, but the main purpose of using this method is to avoid the burden of weighing. Traditionally the method is pen and paper based but the food diary may also be completed either by digital recording or electronically. Although not as complex as the weighed diary, the method requires a detailed explanation of how to carryout the recording of diet that is best done face-to-face. At the end of the assessment period, ideally a trained interviewer should go through the record with the individual to clarify details – this could be done by telephone. A short questionnaire can be included to aid interpretation of the record and provide details of core foods regularly eaten e.g. type of milk and to inquire about non-food items such as dietary supplements. Parents/carers can complete diaries for young children or in addition to children in older age groups. Individuals may record the time, location and whether the respondent was alone or with others for each eating occasion, thus providing information on eating patterns and the social context of eating.
Carrying out a prospective food record can create considerable individual burden (Dwyer, 1999) and there is the risk it may be completed after the food is consumed from memory instead of at the time of intake (Gillman 1994). Another concern is that the process of completing the food record may change eating behaviour (Buzzard 1998, Rockett 2003). The method has been used successfully in many large-scale studies and is an ‘open ended’, flexible method which is not curtailed by a food list and is not subject to interviewer bias. A comparison of methods in the UK arm of EPIC showed that a 7-day diary (estimated record), was in closest agreement to 16 days of weighed intake and next highest correlation with biomarkers compared to a FFQ and a 24 hour recall (Bingham et al, 1997). A study in toddlers also indicated no difference in energy intakes when an estimated diary was compared to a weighed diary (Lannigan et al, 2001).