Acceptability
The validity and feasibility of self-reported dietary intake are influenced by the ways participants respond to the dietary assessment methods. In the present study, participants preferred the 7 d FD because they perceived it as more flexible allowing them to report whenever they had time. The covering of a whole week was seen as giving a more accurate picture of the dietary habits, despite participant was aware of simplifying their food intake, eating less than usual and healthier. Participants felt that the 24 h DR was unfair because it was based on fewer reporting days, days that may not represent ‘normal’ days, due to, for example, attending a party, conference, etc. – even if participants stated that with the 24 h DR they were able to report their intake more precisely and that the assessment method most likely prompted them to report more of the food and beverages they forgot in the 7 d FD. In an American study evaluating participants’ experiences with FD in focus groups, it was also found that participants experienced they simplified their diet. Participants reported consuming simpler foods, foods in predefined portion sizes, ate less frequently, ate fewer snacks and were not eating at restaurants because of the hassle of recording every itemThus, previous research supports the findings in the present study that the 7 d FD leads to more simplified dietary habits and consuming less and probably more healthful foods. This was also reflected in the proportion of UER. For the 24 h DR, it is the memory of previous days’ intake and especially the portion size estimation that is the main reason for misreporting. Even if participants knew the time for the telephone interviews and did some recapturing of the previous 24 h food intake, it was evaluated as difficult. The awareness of the telephone interview and the recapturing of intake could also affect the reported intake in a healthier direction. However, it would be unrealistic with unscheduled interviews, because of the need of participants time for the lengthy 24 h DR and the requirement to cover all weekdays equally.