Dietary Assessment Primer

Food Frequency Questionnaire at a Glance

Purpose

To obtain frequency and, in some cases, portion size information about food and beverage consumption over a specified period of time, typically the past month or year.

Description

A food frequency questionnaire (FFQ) consists of a finite list of foods and beverages with response categories to indicate usual frequency of consumption over the time period queried. To assess the total diet, the number of foods and beverages queried typically ranges from 80 to 120.

Usual portion size can be asked separately for each food and beverage. Alternatively, portion size can be combined with frequency information by asking respondents to translate usual consumption amount to number of specified units (e.g., How often do you eat a ½ cup of rice?). Some questionnaires include portion size images in an attempt to enhance reporting [glossary term:] accuracy.

In addition to foods and beverages, FFQs often ask about the frequency of intake and dosages of commonly consumed [glossary term:] dietary supplements.

FFQs are usually self-administered; interviewer-administration is done occasionally, for example, when literacy is low.

Completing a questionnaire aimed at capturing the total dietary intake usually requires 30 to 60 minutes.

An FFQ is sometimes loosely referred to as a [glossary term:] diet history. However, the term diet history can refer generally to any instrument that asks about diet in the past (Learn More about Diet History). It also is used to refer specifically to a meal-based FFQ or the Burke diet history, which includes a food frequency cross-check component, and its various adaptations.

To learn more about brief frequency questionnaires aimed at capturing particular aspects of the diet, see Screener Profile.

Commonly-used FFQs include the National Cancer Institute's Diet History Questionnaires (DHQ), the Block FFQsExternal Web Site Policy, the Harvard University/Willett FFQsExternal Web Site Policy, and the Fred Hutchinson Cancer Research Center FFQExternal Web Site Policy.

Utility of Data

Limitations of Data

  • Contains systematic error (see Key Concept about Measurement Error). This error can be at least partially mitigated through appropriate statistical modeling, using a less biased dietary assessment method as a [glossary term:] reference instrument, and through [glossary term:] energy adjustment.
  • Detailed information about food preparation, specific food and beverages consumed, and brands, and contextual information about intake (e.g., which foods and beverages are consumed at the same meal) is lacking.
  • Because an FFQ is composed of a pre-specified food list, any single FFQ may not reflect the eating patterns of a given population. Thus, the performance of a particular FFQ in a particular population may not reflect its performance in a different population.

Salient Features Compared to Other Self-Report Instruments

For an at-a-glance comparison of the major features of self-report instruments for assessing diet, including FFQs, see the Comparing Dietary Assessment Instruments table.