What is What We Eat in America, NHANES, and when did it begin?
How often are WWEIA, NHANES data released?
How many days of dietary intake data per respondent are available in WWEIA, NHANES?
What nutrients are included in the WWEIA, NHANES data?
How are the WWEIA data released?
Is it possible to combine data from different release cycles?
There are some individuals who have a record in the Total Nutrients File but no records in the Individual Foods File. Why?

Q What is What We Eat in America, NHANES, and when did it begin?
A 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.

Q How often are WWEIA, NHANES data released?
A 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 2005-2006.

Q How many days of dietary intake data per respondent are available in WWEIA, NHANES?
A 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.

Q What nutrients are included in the WWEIA, NHANES data?
A WWEIA 2001-2002 includes food energy and 60 nutrients/food components (see list). 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 (see list). WWEIA 2005-2006 includes food energy and 63 nutrients/food components, due to the addition of Total Choline (see list).

Q How are the WWEIA data released?
A 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.

Q Is it possible to combine WWEIA data from different release cycles?
A 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:

• Sampling 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 2005-2006 using FNDDS 3.0, 2003-2004 using FNDDS 2.0 and in 2001-2002 using FNDDS 1.0. 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.

Q There are some individuals who have a record in the Total Nutrients File but no records in the Individual Foods File. Why?
A 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. (The number of foods variable name in 2001-2002 is DRXTNUMF and in 2003-2004 is DR1NUMF for Day 1 and DR2NUMF for Day 2.) 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. There was 1 faster in 2001-2002 and 3 in 2003-2004.