What We Eat in America (WWEIA) is the dietary intake interview component of the National Health and Nutrition Examination Survey (NHANES). WWEIA is conducted as a partnership between the U.S. Department of Agriculture (USDA) and the U.S. Department of Health and Human Services (DHHS). DHHS is responsible for the sample design and data collection, and USDA is responsible for the survey’s dietary data collection methodology, maintenance of the databases used to code and process the data, and data review and processing. USDA also funds the collection and processing of Day 2 dietary intake data, which are used to develop variance estimates and calculate usual nutrient intakes.

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). After completion of the in-person interview, an appointment is set for the Day 2 interview. The Day 2 interview is collected by telephone 3 to 10 days following the MEC interview, but not on the same day of the week as the MEC interview.

WWEIA data are collected using USDA’s dietary data collection instrument, the Automated Multiple-Pass Method (AMPM). The AMPM is a fully computerized method for collecting 24-hour dietary recalls either in person or by telephone. In this multiple-pass method, information is collected by 5 standardized steps. The AMPM is a research-based approach designed to enhance efficient collection of complete and accurate food intake data in large-scale national surveys and reduce respondent burden. The AMPM is updated yearly to reflect the changing food supply. Read more about the AMPM.

At the MEC dietary interview, a set of three-dimensional food models are available for the participant to use when reporting amounts of foods. After the Day 1 interview, participants are given USDA’s Food Model Booklet and a limited number of three-dimensional models (measuring cups and spoons, a ruler, and two household spoons) to be used for estimating food amounts during the telephone interview. The Food Model Booklet includes two-dimensional drawings of various sizes of glasses, mugs, bowls, mounds, circles, and other measures.

USDA's Food and Nutrient Database for Dietary Studies (FNDDS) is used for processing the WWEIA dietary intakes. The FNDDS includes comprehensive information that can be used to code individual foods and portion sizes reported by WWEIA participants and also includes nutrient values for calculating nutrient intakes. FNDDS values are updated for every 2-year WWEIA, NHANES release cycle. The FNDDS is available for free download from the USDA's Food Surveys Research Group (FSRG) website. It can be used to enhance analysis of the WWEIA dietary intake data, as well as in coding and analyzing data collected in other studies. Read more about the FNDDS.

Data are released at 2-year intervals. All NHANES files are available for free download from the NHANES website.

All data files are in SAS® transport format (.xpt) and can be used with any package that supports that file format. For general information on downloading the data, consult the frequently asked questions page for the data cycle in question.

Each data release file is accompanied by three additional components:

• Documentation - Includes information about data collection, quality control, data processing, and analytical procedures.
• Codebook - Includes names assigned to each data item, question text, response categories, valid values, and other information. 
• Frequencies - Includes raw frequency counts for all variables in the data file.

To receive an e-mail notice from FSRG when new WWEIA data are released, you may join the FSRG listserv.

For each 2-year data release cycle, the following dietary intake data files are available:

• Individual Foods File - Contains one record per food for each survey participant. Foods are identified by USDA food codes. Each record contains information about when and where the food was consumed, whether the food was eaten in combination with other foods, amount eaten, and amounts of nutrients provided by the food.
  
  
• Total Nutrient Intakes File - Contains one record per day for each survey participant. 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 diet to lose weight or for other health-related reason and type of diet; and frequency of fish and shellfish consumption (examinees one year or older, Day 1 file only).
  

This tutorial walks you through the steps of conducting an analytical project from beginning to end, with examples of many common analytic procedures. Click here to open up a new window at the NCHS website.

What We Eat in America (WWEIA), NHANES is a national food survey conducted as a partnership between the U.S. Department of Health and Human Services (DHHS) and the U.S. Department of Agriculture (USDA). WWEIA represents the integration of two nationwide surveys - USDA's Continuing Survey of Food Intakes by Individuals (CSFII) and HHS' NHANES. Under the integrated framework, DHHS is responsible for the sample design and data collection. USDA is responsible for the survey's dietary data collection methodology, development and maintenance of the food and nutrient databases used to code and process the data, and data review and processing. The two surveys were integrated in 2002.

Data are released every two years as one dataset. The first WWEIA, NHANES data release was for 2001-2002. The most recent data release is 2009-2010.

Beginning with the 2003-2004 data release, two days of dietary intake data are available per respondent. The 2001-2002 release includes one day of dietary intake data. Data collection for 2002 included a second dietary recall (Day 2). Because of confidentiality reasons concerning release of single-year data, dietary data for Day 2 were not publicly released.

• WWEIA 2001-2002 includes food energy and 60 nutrients/food components.
• WWEIA 2003-2004 includes food energy and 62 nutrients/food components, due to the addition of values for added vitamin B12 and added vitamin E.
• WWEIA 2005-2006 includes food energy and 63 nutrients/food components, due to the addition of total Choline.
• WWEIA 2007-2008 includes food energy and 64 nutrients/food components, due to the addition of Vitamin D (D2 + D3) (see list).
• WWEIA 2009-2010 includes food energy and 64 nutrients/food components.

WWEIA data are posted on the NHANES Examination File web pages for the respective survey year. There are two types of WWEIA data files, the Dietary Interview Individual Foods File and the Dietary Interview Total Nutrients File. The data are in SAS® transport format with a .xpt filename extension. Accompanying the data files are additional files containing codebooks, documentation, and frequencies.

Yes, the sample design for NHANES makes it possible to combine data cycles in order to increase the sample size and analytic options. However, in order to combine cycles appropriately, researchers must pay attention to variations between data cycles, including the following:

• Sample weights - As a general rule, consult the version(s) of the NHANES analytic guidelines that correspond to the data cycles in question. To combine data from different cycles, it is necessary to use the same type of sampling weight from both cycles. For example, when combining dietary data from WWEIA 2003-2004 with WWEIA 2001-2002, use the special dietary intake data weights from both cycles and follow the specific instructions given in the analytic guidelines (e.g., on p. 12 of the Sept. 2006 revision of the Dec. 2005 update). Dietary intake data weights for 2001-2002 are slated for release in late 2006. Researchers wishing to analyze data before those weights are released will have to use the 2-year MEC weights (WTMEC2YR, provided in the Demographics File) from both cycles and follow the instructions given in the analytic guidelines.
• Number of days - The same number of days from each data cycle should be used. This is of particular importance in combining dietary data from WWEIA 2003-2004 with WWEIA 2001-2002, because only Day 1 data were publicly released for 2001-2002.
• Food and nutrient database - Data collected during each WWEIA cycle are coded using the most up-to-date food composition values available for the time frame. Nutrient intakes were calculated in 2007-2008 using FNDDS 4.1, 2005-2006 using FNDDS 3.0, 2003-2004 using FNDDS 2.0 and in 2001-2002 using FNDDS 1.0. Values for Vitamin D (D2+D3) were included in FNDDS 4.1 and were used for WWEIA, NHANES 2007-2008. Values for total Choline were included in FNDDS 3.0 and were used for WWEIA, NHANES 2005-2006. Values for added vitamin B12 and added vitamin E were included in FNDDS 2.0 and were used for WWEIA, NHANES 2003-2004. Since added vitamins B12 and E were not available in FNDDS 1.0, they are not present in the WWEIA, NHANES 2001-2002 data. Other changes that occurred in FNDDS between versions 1.0 and 2.0 are discussed in the version 3.0 documentation. Other changes that occurred between the two release cycles are discussed in the documentation for the 2003-2004 Individual Foods Files.

A small number of WWEIA respondents ate no food on the survey day. They are referred to as "fasters." They can be identified by searching for records in the Total Nutrients File with the number of foods equal to zero. Fasters' intake records are considered to be complete, even though they did not report any foods or beverages. For all nutrients, they have a value of zero.