Two days of 24-hour dietary recall data are collected in WWEIA, NHANES. The Day 1 interview is conducted in person in the Mobile Examination Center (MEC). The Day 2 interview is collected by telephone 3 to 10 days later, but not on the same day of the week as the Day 1 interview.
Trained interviewers using the 5-step USDA Automated Multiple-Pass Method (AMPM) collect dietary intakes. The AMPM includes an extensive compilation of standardized food-specific questions and possible response options. Routing of questions is based on previous response. The AMPM is revised for each 2-year collection of WWEIA to reflect the changing food supply. Read more about the AMPM.
During the 24-hour recall, respondents estimate the amount of food and beverages consumed using 3-dimentional models on Day 1 and the USDA’s Food Model Booklet on Day 2.
|For each food and beverage consumed during previous 24-hour period||Detailed description|
|Additions to the food/beverage|
|What foods/beverages were eaten in combination|
|Time eating occasion began|
|Name of eating occasion|
|Food/beverage source (where obtained)|
|Whether food/beverage was eaten at home|
|Amounts of energy and 60+ nutrients/food components provided by the amount of food/beverage|
|For each respondent on each day||Day of the week|
|Amount and type of water consumed: total plain water, total tap water, and total bottled water|
|Source of tap water|
|Daily intake usual, much more or much less than usual|
|Use and type of salt at table and in preparation (Day 1 only)|
|Whether on a special diet and type of diet (Day 1 only)|
|Frequency of fish and shellfish consumption (respondents 1 year of age and older, Day 1 only)|
|Daily total intakes of energy and 60+ nutrients/food components|
The WWEIA, NHANES data includes food energy and 64 nutrients/food components. The number of nutrients has increased over the years. Click on List of Nutrients to see the full list and the years added.
USDA's Food and Nutrient Database for Dietary Studies (FNDDS) converts food and beverages consumed in WWEIA into gram amounts and determines their nutrient values. Because the FNDDS generates the nutrient intake data files, researchers do not need to use the FNDDS to estimate the nutrient intake for the survey respondents. The FNDDS is revised for each 2-year cycle of WWEIA and available for download from the USDA's Food Surveys Research Group (FSRG) website. Read more about the FNDDS.
WWEIA data are released every two years on the NHANES Dietary File. The first WWEIA, NHANES data release was for 2001-2002. The most recent data release is 2017-2018. Beginning with the 2003-2004 data release, two days of intake are available per respondent. There are two types of WWEIA data files for Day 1 and for Day 2:
- Individual Foods File - Contains one record for each food or beverage consumed, identified by USDA food codes, for each survey respondent. Each record contains gram amount consumed; food energy and nutrient intake; whether the food was eaten in combination with other foods; time and eating occasion; source of food (where obtained) and if eaten at home.
- Total Nutrient Intakes File - Contains one record per day for each survey respondent. Each record contains daily totals of food energy and nutrient intakes, daily intake of water, intake day of week, total number foods reported, and whether intake was usual, much more than usual or much less than usual. The Day 1 file also includes salt use in cooking and at the table; whether on a special diet and type of diet; and frequency of fish and shellfish consumption (respondents one year or older).
Accompanying the data files are additional components:
- Documentation - Includes information about data collection and processing, quality control, and analytical procedures.
- Codebook and Frequencies - Includes variable name and label, question text, and frequency count by code/value description for each variable.
Yes, for combining release cycles, please refer to the NHANES Analytic Guidelines. For dietary data, it is also important to consider changes in foods and beverages, including nutrient values, between survey time periods. FNDDS, the database used to determine the nutrient values in WWEIA, is revised for each 2-year cycle of WWEIA. Read more about the FNDDS on the FSRG website.
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