Food supply data for a country, such as food balance sheets (FBSs) or food disappearance data provide annual estimates of the national availability of food commodities. These data may also be used to calculate the average per capita availability proteins and other nutrients. The major limitation of national food supply data is that they reflect food availability rather than food consumption. Losses due to cooking or processing, spoilage, and other sources of waste as well as additions from subsistence practices cannot easily be assessed. According to the World Health Organization (WHO), FBS consumption estimates tend to be about 15% above the consumption estimates derived from household surveys or national dietary surveys.
FBS data are useful for tracking trends in the food supply and for determining availability of foods that are potentially important sources of nutrients or chemicals, and for monitoring of food groups targeted for control.
Information regarding food availability or consumption at the household level may be collected by determining the foodstuffs purchased by a household, or by surveying the household to determine what foods were consumed by the household. Such data are useful for comparing food availability among different communities, geographic areas, and socioeconomic groups, and for tracking dietary changes in the total population and within population subgroups. However, these data do not provide information on the distribution of food consumption among individual members of the household.
Food diary/food record surveys. The food diary (sometimes called food record) surveys ask the subject or a surveyor to report all foods consumed during a specified period. These surveys generally collect information not only about the types of food consumed but also about the source of the foods (e.g., store-bought, home-cooked), the time of day, and place that foods are consumed. Amounts of each food item consumed may or may not be recorded, depending on the study objectives. However, in order to calculate nutrient intakes it is highly desirable to quantify the intakes and to record the amounts consumed as accurately as possible.
Dietary recall survey. The dietary recall consists of listing foods and beverages (including drinking water and sometimes dietary supplements) consumed during some previous period, usually the previous day or during the 24 hours prior to the recall interview. These surveys generally collect information not only about the types and amounts of food consumed but also about the source of the foods (e.g., store-bought, home-cooked), the time of day, and place that foods are consumed. Foods and drinks are recalled from memory. The interview may be conducted in person, by telephone, or increasingly via the Internet.
Food frequency questionnaire. The food frequency questionnaire (FFQ), sometimes referred to as a list-based diet history, consists of a listing of individual foods or food groups. For each item on the food list, the respondent is asked to estimate the number of times the food is usually consumed per day, week, month, or year. The number or types of food items may vary, as well as the number and types of frequency categories. FFQs may be unquantified, semiquantified, or completely quantified. The unquantified questionnaire does not specify serving sizes, whereas the semiquantified tool provides a typical serving size. A completely quantified FFQ allows the respondent to indicate any amount of food typically consumed. Some FFQs include questions regarding the usual food preparation methods, trimming of meats, use of dietary supplements, and identification of the most common brand of certain types of foods consumed.
The validity of dietary patterns assessed with FFQ depends on the representativeness of the foods listed in the questionnaire and the ability of a respondent to accurately complete the questionnaire. FFQs are commonly used to rank individuals by consumption of selected foods and/or nutrients. Although FFQs are not designed to be used to quantitatively measure food consumption, the method may be more accurate than other methods for characterizing long-term consumption practices. FFQs may focus on one or several specific nutrients or food chemicals and may include a limited number of food items. In addition, FFQs can be used in the identification of absolute nonconsumers of certain foods.
Diet history survey. The meal-based diet history is designed to assess usual individual food consumption. It consists of a detailed listing of the types of foods and beverages commonly used at each eating occasion over a defined time period, which is often a "typical week." A trained interviewer probes for the respondent's customary pattern of food consumption on each day of the typical week. The reference time frame is often over the past month or the past several months, or may reflect seasonal differences if the reference time frame is the past year.
Food habit questionnaire. The food habit questionnaire may be designed to collect either general or specific types of information, such as food perceptions and beliefs, food likes and dislikes, methods of preparing foods, use of dietary supplements, and social settings surrounding eating occasions. These types of information are frequently included along with the other four methods, but may also be used as the sole basis for data collection. These approaches are commonly used in rapid assessment procedures. The questionnaire may be open-ended or structured, self- or interviewer-administered, and may include any number of questions depending on the information desired.
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