A 24-h dietary recall is a structured interview in which detailed questions are asked about all foods and beverages consumed over the previous 24 h. Dietary recall interviews can be conducted in person or by telephone and typically last 20-30 min. Data from 24-h recalls have been used to characterize large populations in the United States via the survey, "What We
Eat in America" (Conway et al, 2004; Dwyer et al, 2003a). When conducted in large population groups, recalls provide a general "snapshot" of population dietary intake.
Regardless of whether 24-h dietary recalls are done in-person or over the telephone, the protocols work best when interviewer scripts are standardized on a computer screen with direct data entry into a software program. It is very important that the interviewer be well trained since tone of voice, body posture (when inperson), and reactions to participant descriptions of foods consumed can influence the quality of the data, including omissions or phantom food additions (Conway et al, 2004). Sometimes interviewers need to redirect the conversation back to the structured questions, should the respondent deviate off-topic, which can be a problem when assessing specific population subgroups, such as the elderly. As with food records, the use of portion size estimate aides, such as life-size food models, photographs, or dimensional aides including rulers and measuring cups, increases the ability to estimate portion size thereby improving the reliability of the recall data (Pietinen et al, 1988; Williamson et al, 2003).
Regarding the actual process of conducting the 24-h recall interviews, the currently most widely accepted methods follow the protocol established by the United States Department of Agriculture (USDA) and used in the "What We Eat in America" survey (Conway et al, 2003; Dwyer et al, 2003a, b). This five-step method includes the following sequence of queries:
1) Quick list - trained interviewers first ask participants to list all foods and beverages consumed during the previous 24 h.
2) Forgotten food list - interviewer asks detailed probes about foods or additions to foods that are frequently forgotten. Examples of foods that are often added to this list are milk on cereal, sugar in coffee, and between-meal snacks and beverages.
3) Time and place - the interviewer asks the participant to recall the time of day and the location (e.g., home, school, restaurant) of the food consumption. This time and place memory probe frequently helps participants to better recall the foods consumed.
4) Detail cycle - the interviewer probes for details about each food named in the quick list and forgotten list, including cooking methods, portion size, brand names, type, and amount of fat added during cooking and at the table. The detail cycle includes the collection of information on mixed dishes and recipes. The questions in the detail cycle are highly standardized with computerized prompts to ensure uniform data collection.
5) Final review - the interviewer does a final review of the foods and beverages consumed and queries participants about any additional items that may have been omitted.
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