Introduction
New nationwide dietary intake data for the years 2001-2002 are now available for public use. The year 2002 was the first year of full integration of two nationwide dietary intake surveys – the Continuing Survey of Food Intakes by Individuals (CSFII) conducted by the U.S. Department of Agriculture (USDA) and the National Health and Nutrition Examination Survey (NHANES) conducted by the U.S. Department of Health and Human Services (HHS). The new integrated survey is called What We Eat in America and is collected as part of NHANES. Data collection for What We Eat in America will be on a continuous yearly basis. Two days of data will be collected for all respondents, and the Day 2 interview will be conducted by telephone. What We Eat in America food intake data can be linked to health status data from other NHANES components, allowing researchers to explore relationships between dietary intakes and health status.
Under the integrated framework, HHS 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.1 USDA is also funding the collection and processing of Day 2 data. Because NHANES is on a two-year data release cycle, the 2001-2002 dataset includes NHANES data collected in 2001 along with What We Eat in America data collected in 2002. Collection and processing procedures for the two years were similar.
Sample design and sample size
NHANES is a multistage, stratified area sample that is representative of the civilian noninstitutionalized population of the U.S. Certain groups were oversampled to allow for more precise estimates. Oversampled groups include adolescents 12-19 years, persons 60+ years, African Americans, Mexican Americans, low-income persons, and pregnant women. Each annual sample is nationally representative, but the 2-year sample should be used to provide adequate sample sizes for subgroup analyses. Of the 13,156 persons eligible for the survey in 2001-2002, 80 percent (n=10,477) participated in a physical examination at the mobile exam center, and 74 percent (n=9,701) had complete and reliable Day 1 dietary interview data. Read more about NHANES.
Food and nutrient intake data files
The 2001-2002 data files are available for free download from the NHANES 2001-2002 data release page. Two files are available – one that includes information about each food a survey participant consumed in a 24-hour period and another containing a summary of daily nutrient intakes for each participant. These files contain raw, unanalyzed data. Summary data tables containing estimates of usual nutrient intakes and a comparison of those intakes to the Dietary Reference Intakes will be available on the FSRG website later this year. The estimates will be based on 2001-2002 data and will include only nutrients obtained from foods, not supplements. To receive an e-mail notice when the estimates are made public, join the FSRG listserv.
The data files are available in SAS transport format and can be used with any package that supports that file format. The two dietary intake data files are named DRXIFF_B and DRXTOT_B. For general information on downloading the data, review the answer to
question 4 in the NHANES 2001-2002 Data Release Frequently Asked Questions.
- DRXIFF_B contains one record per food for each survey participant. Each record identifies the day of the week on which the interview was conducted and the time and name of the eating occasion at which the food was eaten, as well as the following food-specific data:
- Food code
- Amount eaten (in grams)
- Amounts of energy and 60 nutrients/food components
 in units appropriate to the nutrient
- If the food was eaten as part of a combination, the combination type (e.g., salad ingredients coded separately, milk added to cereal) and a variable linking the items within the combination
- DRXTOT_B contains daily aggregates of total energy and nutrient intakes and intake of water for each respondent; and frequency of fish and shellfish consumption for each child 1 to 5 years and each woman 16 to 49 years.
- Related files – Each data file is accompanied by 3 additional PDF files:
- Codebook – includes names assigned to each data item, question text, response categories, valid values, and other information
- Documentation – includes information about data collection, quality control, data processing, and analytical procedures
- Frequencies – includes raw frequency counts for all items in the data file
- Demographic variables for NHANES 2001-2002 are contained in the demographic file. Variables include age, gender, race/ethnicity, education, country of birth, Poverty Income Ratio, income, marital status, and pregnancy status. The 2001-2002 dietary files can be linked to these demographic variables by the survey participant identification number (variable name SEQN), which is found in all NHANES files.
The NHANES 2001-2002 demographic file also includes survey design variables such as sample weights. To learn more about using the sample weights and analyzing the NHANES data, review the NHANES analytic guidelines. Instructions on
how to merge selected demographic variables with data files are available from NHANES.
- Restricted data – As a precaution to protect the confidentiality of survey participants, single-year data from NHANES are not released for public use. For that reason, only Day 1 interview data are included in the present release. Neither the data collected on Day 2 in What We Eat in America 2002 nor Day 1 information that was only collected in 2002 (e.g., the place where each food was obtained) will be publicly released. Restricted data, such as those just mentioned, may be made available at the Research Data Center located at the National Center for Health Statistics (NCHS) headquarters in Hyattsville, MD. A research proposal for using the restricted data must be submitted to NCHS for review and approval. Instructions for requesting use of these data are available from the NCHS Research Data Center. Beginning with the 2003-2004 release, two days of data will be publicly available, as well as information on where each reported food was obtained.
Food and Nutrient Database for Dietary Studies
The USDA Food and Nutrient Database for Dietary Studies (FNDDS), 1.0, was used to process the 2001-2002 dietary intake data. The FNDDS includes comprehensive information that can be used to code individual foods and portion sizes and contains nutrient values for calculating nutrient intakes. It can be used to enhance analysis of the 2001-2002 dietary intake data, as well as in coding and analyzing data collected in other studies. Read more about FNDDS.
Pyramid Servings Database
The Food Guide Pyramid is a general guide for choosing foods to eat each day. The Pyramid specifies numbers of servings to eat from five major food groups (grain, vegetable, fruit, dairy, and meat) and includes advice about intakes of fat and sugar. USDA's Pyramid Servings Database provides the means for assessing the adequacy of the U.S. population's food intakes in terms of Pyramid servings. Now updated with FNDDS data for 2001-2002, the Pyramid Servings Database is available for free download from the website of USDA's Community Nutrition Research Group.
References
- Dwyer J, Ellwood K, Moshfegh AJ, and Johnson CL. (2001). Integration of the Continuing Survey of Food Intakes by Individuals and the National Health and Nutrition Examination Survey. J Am Diet Assoc 101(10):1142-3.
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