NHANES III Dietary Interview Component Dietary interviews were administered to all examinees by a trained dietary interviewer in the mobile examination center (MEC). Respondents reported all foods and beverages consumed except plain drinking water (i.e., not bottled) for the previous 24-hour time period (midnight to midnight). An automated, microcomputer-based dietary interview and coding system known as the NHANES III Dietary Data Collection (DDC) System was used to collect all NHANES III dietary recall data. The DDC system was developed for use in the survey by the University of Minnesota's Nutrition Coordinating Center (NCC). The dietary interviews were conducted in English and Spanish by bilingual dietary interviewers in a private room to ensure confidentiality. Proxy respondents were permitted for infants and children aged two months through five years and for other respondents who were unable to report on their own. Children aged six to 11 years were permitted to report their own intake if the interviewer deemed it acceptable and appropriate, but many interviewers for respondents in this age category were completed by proxy or with the child and a proxy. The dietary interviewers contacted other information sources such as care providers and schools to obtain complete dietary intake data for respondents. The primary source of food composition data for NHANES III is the U.S. Department of Agriculture (USDA) Survey Nutrient Database; two nutrient files were provided by USDA for use in NHANES III (USDA 1993, 1995). Each USDA file contained food composition values that were appropriate for the time period during which the NHANES III data were collected. Additionally, food composition data for a small number of herbs and spices were obtained from NCC (NCC, 1996). The DDC system's foods database was designed specifically to handle time-related changes in food descriptions, food amounts, and recipes; updated information was applied retrospectively to data collected in the early part of NHANES III. As was mentioned earlier, two USDA food composition databases were used to assign nutrient values to the NHANES III dietary recalls (USDA 1993; USDA, 1995). In addition to data changes that occurred in the nutrient values of foods due to food product reformulations, recipe changes, and so forth, the U.S. marketplace underwent tremendous growth and change as new food product lines were introduced and new food components were added to the food supply (e.g., fat substitutes and artificial sweeteners). The impact of these and other changes may require additional analysis. Dietary recall interviews were edited by the interviewers to ensure that they were as complete as possible. NCHS completed all final editing and determinations regarding the completeness and reliability of the dietary recalls. Analysts should note that the data reported are self-reported data. Extreme values were verified. Information pertaining to the use of nutritional supplements and antacids was reported separately during the Household Adult and Household Youth Interviews. A number of quality-control monitoring techniques were employed during the survey. The techniques for monitoring the Dietary Interview component included observations of actual dietary interviews and reviews of audiotape interviews by NCHS and contractor staff. In addition, the dietary interviewers worked in two-person teams; there was one team in each MEC. The dietary interviewers performed 10-percent cross-check reviews of their partners' work using printed recall reports. Finally, newsletters, field memoranda, telephone calls, and staff retraining sessions were other methods used to maintain quality control during the survey. Refer to the NHANES III Dietary Interviewer's Training Manual for the dietary interview protocol (U.S. DHHS, 1996b). Analysts are encouraged to use six years of survey data in their analyses. The reliability of estimates is improved when larger sample sizes are used. For more detailed information, see the Analytic and Reporting Guidelines for NHANES III (U.S. DHHS, 1996b). In addition, MEC final examination weights (WTPFEX6) should be used when analyzing the total nutrient intake data and related questionnaire data in this file. For more information on the use of sample weights in NHANES III data analysis, refer to the NHANES III Analytic and Reporting Guidelines (U.S. DHHS, 1996b). NHANES III Total Nutrient Intakes and Foods Data Files NCHS prepared 4 datasets that are based on the 24-hr dietary recall interview. Total nutrient intakes were reported in the NHANES III Examination Data file (Catalog 76200). Three foods files were prepared; three files are found in Catalog 76700: NHANES III Individual Foods Data File from the Dietary Recall; NHANES III Combination Foods Data File from the Dietary Recall; NHANES III (Variable) Ingredients Data File from the Dietary Recall. Documentation was prepared for each of the foods data files. Data users are encouraged to review all of the documentation prior to using the data files. Look-up Tables for the NHANES III Foods Data Files Textual descriptions for several NHANES III Foods Data File numeric code variables are located in an Appendix section that accompanies the Foods Data Files. The Appendix files are referred to as "look-up" tables throughout the data file documentation for the Foods Data Files. Computer code is provided so that data users can merge the foods data files with the information in the Appendix/look-up tables. Variable Ingredients File Ingredient Information The approach used to classify elemental foods and recipe foods was described in the NHANES III Individuals Foods File documentation. The Individual Foods File provides information about the component foods that were reported during the dietary interview. Many component foods were recipe foods. Recipe foods have ingredient records, some of which were variable ingredients. Variable ingredients were ingredients that the respondent could specify during the interview. Many types of ingredients were variable; the DDC System targeted sources of fat and sodium in food. Information about variable ingredients is reported in the NHANES III Variable Ingredients File (VIF). An important concept to understand when using the NHANES III foods files is that many foods can be component foods as well as ingredients of component foods, depending on their use. For example, margarine is included in the Individual Foods File as a component food. Two examples of margarine as a component food were margarine spread on bread and margarine added to mashed potatoes at the table; in both examples, margarine is a component food and has a food gram weight, USDA food code, possibly a brand name, nutrients, and so forth. The SAME margarine product may also be used as an ingredient in a recipe food such as homemade cookies. If a respondent reported eating homemade cookies, a probe as to the type of fat used in the recipe was asked during the interview. The Individual Foods File record for this food would report the type of cookie, the amount eaten, and nutrients for the cookie. The Variable Ingredients File (VIF) reports information about the margarine ingredient that was used to prepare the cookies; the VIF record includes a USDA food code for the margarine and possibly a brand name. The VIF reports information pertaining to the variable ingredients for many recipe foods in the Individual Foods File. Only ingredients that the survey respondents were asked to specify are included in the VIF; other recipe ingredients that were not presented to respondents are excluded from the VIF. For example, if a respondent reported eating tuna salad, the variable ingredient probes included a probe as to the type of tuna fish, a probe as to whether the tuna was rinsed or drained, and a probe as to the type of mayonnaise or salad dressing used. The VIF provides information about these variable ingredients. On the other hand, the tuna salad may also have celery, pickles, and onion ingredients, but these ingredients were not variable ingredients. Again, the DDC System variable ingredient probes targeted sources of fat and sodium in the diet. Notes to Data Users: 1. Atypical Recipes and Modified Recipes If a respondent reported that a food was prepared using what might be considered to be atypical or unusual ingredients, the dietary interviewers noted this. For example, some respondents used yogurt instead of mayonnaise to prepare salads. Additionally, respondents added unusual components to foods. The interviewers were instructed to note information about the ingredients that were used to prepare foods. NCHS evaluated the interviewers' notes and finalized the entries for all foods reported during the survey. Respondents also modified recipes by omitting fat, substituting lower fat ingredients, using egg substitute products instead of whole eggs, etc. The recipe information that was recorded during the dietary interview was used to modify a standard recipe or locate another suitable recipe so that the food could be entered into the DDC System as a multi-component/combination food. Modified recipe food components included ingredient-type items such as flour and salt. The Individual Foods File reports the component level information. The multi-component foods have descriptive data in the Combination Foods File. 2. Default Ingredients in the VIF Respondent-specified variable ingredients are reported in the VIF. If the respondent did not know anything about the ingredients that were used to prepare a food, the DDC System assigned a default ingredient automatically. There are default ingredients for home-prepared and commercially-prepared foods. For example, if a respondent reported eating brownies that were purchased at a bakery, and the fat ingredient information was unknown, the DDC System default for commercial brownies, purchased at a bakery would be assigned to the food. Similarly, ingredients that were used to prepare home-prepared foods also had default ingredient options. If a respondent ate a homemade meatloaf and could not specify the type of meat used, the DDC System assigned a default ingredient to the ingredient probes for the food. The variable ingredient default code (DRPVIDC) denotes when default variable ingredients were assigned to foods; the DRPVIDC codes have a descriptive text with them. For example, the type of fat used to fry a commercial food might be unknown so the DRPVIDC description might read: "fat used in frying unknown-commercially prepared". 3. No Ingredients Added If the respondent stated that variable ingredients were not used to prepare a particular food, the VIF will include an ingredient record for the omitted ingredient(s), but the ingredient food code (DRPICODE) field is blank for each omitted ingredient. The ingredient identification code (DRPINGID) links to a look-up table called IDCODE that provides text descriptions for the omitted ingredients. For example, cooked vegetables have fat and salt ingredient probes. If the respondent stated that no fat or salt was added in preparation, the VIF ingredient identification code (DRPINGID) descriptions for each variable ingredient will link to text information stating that no fat or salt was added in preparation. Note: The same look-up table called "IDCODE" is used for Food Identification Code (DRPFID) and Ingredient Identification Code (DRPINGID) text descriptions. DRPFID provides component level information as described in the Individual Foods File documentation; DRPINGID provides ingredient level information found in the VIF. Summary The VIF provides information about respondent-specified variable ingredients, including default variable ingredients. The VIF variables are sorted by case, meal number (DRPMN), food number (DRPFN), component number (DRPCN) and ingredient number (DRPIN). All variable ingredients that were added to a recipe food have a food code (DRPICODE); ingredient food codes link to food code descriptions in the look-up table "Codebook". If a variable ingredient was reported by brand name, this information was included in the VIF; the brand name code (DRPCOMM) is linked to a brand name description in a look-up table called "BRANDS". The ingredient identification code (DRPINGID) for all variable ingredients provides descriptive information about variable ingredients; DRPINGID is linked to the look-up table "IDCODE".