Task 2: Key Concepts About NHANES Dietary Data Collection


NHANES Data Collection

NHANES collects data using interviews, physical examinations, and questionnaires:


NHANES Dietary Data Collection

Three major types of dietary data are collected in NHANES:

Dietary Behavior

During the household interview, information is obtained on dietary behavior including topics such as dietary modifications due to health conditions, and dietary supplement use.  Demographic, socioeconomic and other health-related questions are also administered. 


24-hour Recalls

During the MEC exam, a 24-hour dietary recall is administered in addition to medical and dental examinations, physiological measurements and laboratory tests.  The 24-hour recalls are conducted in English or Spanish.  These dietary interviews are conducted by dietary interviewers. Survey participants 12 years and older complete the dietary interview on their own. Proxy respondents report for children who are 5 years and younger and for other persons who cannot self-report.  Proxy-assisted interviews are conducted with children 6-11 years of age. Beginning in 2002, all participants were asked to complete a second 24-hour dietary recall (Day 2) interview.  The NHANES Day 2 dietary recalls are collected by telephone approximately 3 to 10 days after the MEC exam. Before NHANES 2002, a second 24-hour recall was collected on a small subset of participants.


The following table shows the data that are collected for the two 24-hour recalls.


Food and Participant Data Collected During the Two 24-Hour Recall
Link Description

Information specific to each food and beverage consumed on a recall day:

  • Detailed description (type, form, brand name)
  • Additions to the food
  • Amount consumed
  • What foods were eaten in combination
  • Time eating occasion began
  • Name of eating occasion
  • Food source (where obtained)
  • Whether food was eaten at home
  • Amounts of food energy and more than 60 nutrients/food components provided by the amount of food (calculated)

Information specific to the recall day:

  • Day of the week (recall day)
  • Amount and type of water consumed, including total plain water, tap water, and plain carbonated water
  • Recall day's consumption amount compared to typical diet
  • Daily total intakes of food energy and more than 60 nutrients/food components (calculated)

Information specific to a participant's overall diet:

  • Source of tap water
  • Added salt: Frequency and type of salt added at the table and when preparing food
  • Whether on a special diet and type of diet
  • Frequency of fish and shellfish consumption (past 30 days)


Interviewers administer the 24-hour recall using USDA’s Automated Multiple-Pass Method (AMPM). This figure shows how the data are collected in 5 standardized steps:


USDA Automated Multiple-Pass Method (AMPM)

diagram showing 5 step interview process


Food Frequency Questionnaire

The Food Frequency Questionnaire (FFQ) was mailed to respondents following completion of the second 24-hour recall in NHANES 2003-2006.  The FFQ collects information on the frequency of consumption of foods and food groups during the previous 12 months. Additional information on types of foods consumed, such as sugar-free soft drinks; whole grain foods; and light, low-fat, or fat-free foods, was also included.  The National Cancer Institute (NCI) developed the FFQ based on its Diet History Questionnaire (DHQ), a food frequency instrument that is widely used in nutritional epidemiology research.  The DHQ food item list was compiled using data from the 1994-1996 CSFII. The "Related References" page includes several research articles on the development and validation of the DHQ and NHANES FFQ instruments and the uses of FFQ data in research. NHANES participants who completed both 24-hour recalls were mailed the FFQ component. English and Spanish versions of the FFQ instrument were used. Unlike the DHQ, portion size information was not collected.  The FFQ results are not intended to be used for nutrient intake estimation, but rather to assess usual dietary intake.

As with the 24-hour recall, survey participants 12 years and older provide their own responses for the food frequency questionnaire. Proxy respondents report for children who are 5 years and younger and for other persons who cannot self-report; and proxy respondents assist children 6-11 years of age.



For more information about the history of Dietary Data collection by USDA and NHANES and the integrated system, see the "Related References" page.

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