For this method a dietitian or a trained interviewer asks an individual to recall all foods consumed in the past 24 hours. The interviewer prompts the individual for information on brand names, portion sizes, recipe ingredients, cooking methods, condiments, and beverages. If the interview is conducted in person, food models and household measuring instruments may be used to increase the accuracy of portion sizes. The interviewer must be highly trained to capture detailed information and to conduct the interview in a non-judgmental manner. People are often reluctant to divulge poor dietary habits, especially if the interviewer exhibits any reaction to what the person is saying. Those who consume high quantities of foods often underreport their intake; individuals with low intakes often exaggerate their reports.
The 24-hour recall method is more appropriate for assessing the intake of large populations than of individuals. Usual intake of an individual cannot be captured by a one-day recall. If applying the method to a large population, the sample population should be representative of the population that is being studied and interviews should take place on different days of the week in order to reflect both weekday and weekend eating patterns.
In this method of assessment, individuals are asked to record food intake over a specified period of time. They are instructed to record details such as brand names, portion sizes, recipe ingredients, cooking methods, condiments, and beverages. The individual may be given measuring instruments or food models if possible to ensure accurate reporting of portion sizes. It is best to review the food record afterwards as well, and query the individual for details that are omitted. Food records may be collected for any length of time but are usually collected for three to seven days. It is recommended to include weekend days in the recording period.
In compiling these records, the subject is instructed to weigh all recipe ingredients and foods consumed. The same details required of food records are recorded. The weighed-food record is the most accurate record of individual food intake, though it does require the subject to be motivated and able to weigh and record accurately.
The dietary history method of assessment is used to evaluate usual intake in an individual over a long period of time. The subject is asked questions about his or her usual eating patterns. Test administrators may ask such questions as "What do you usually eat first in the day?" or "How often do you eat [certain food]?" This method may also include a 24-hour recall and/or food record to supplement the information obtained. Note that the dietary history is rather labor intensive and the information obtained is more qualitative than quantitative.
A food frequency questionnaire (FFQ) is used to determine the frequency of consumption of certain foods. It contains a list of foods and a series of frequencies such as "daily," "three times a week," "monthly," etc. Respondents check off the frequency in which they eat each food on the supplied list. The food frequency provides qualitative data on types and frequency of foods or food groups. A semi-quantitative food frequency questionnaire provides a ranking classification of individuals into low, medium, and high intakes of specific nutrients and is used to examine associations between nutrients and disease. The questionnaire must contain enough foods that are good sources of the nutrient of interest in order to discriminate between low and high consumers. The FFQ can examine current diet or diet in the recent or remote past.
Newer methods of dietary assessment include the use of videotaping or photographing foods that are eaten. The photographing can be done either by the individual wwhose data is being collected, or by the study team. Videotaping can be quite accurate if the camera remains at a standardized distance from the food and at a specific angle. This method would not be feasible for large surveys. Having individuals photograph their own food can result in pictures in which portion sizes may be difficult to ascertain, or foods difficult to identify. However, standardized photographs of foods of known weight and volume can be used as standards by which to estimate portion sizes.