Food Frequency Questionnaire
Food Frequency Questionnaire — A food frequency questionnaire (FFQ) is a structured dietary assessment instrument that asks respondents how often they consumed each of a defined list of foods over a specified period (typically the past month or year). FFQs are designed to estimate usual long-term intake patterns and are widely used in nutritional epidemiology, but carry known portion estimation and recall biases.
What is a food frequency questionnaire?
A food frequency questionnaire (FFQ) is a self-administered or interviewer-administered instrument in which respondents indicate how frequently they consume each item on a predefined food list. Frequency response options typically include categories like:
- Never or less than once per month
- 1-3 times per month
- Once per week
- 2-4 times per week
- 5-6 times per week
- Once per day
- 2-3 times per day
- 4-5 times per day
- 6+ times per day
Many FFQs also collect typical portion size for each food (small / medium / large). The Block FFQ, Willett FFQ (Harvard), and NHANES Diet History Questionnaire are widely used research instruments.
How does an FFQ work?
The respondent’s chosen frequency × portion is multiplied by the average nutrient content of each food (drawn from a food database) to estimate average daily nutrient intake over the recall period. A typical FFQ takes 30-60 minutes to complete and includes 100-200 food items.
FFQs are most useful when the research question concerns usual intake over months or years (nutritional epidemiology, chronic disease risk research). They are less useful for short-term changes or precise daily accounting.
Why FFQs matter
The major published associations between dietary patterns and disease — Mediterranean diet and cardiovascular disease, fiber and colorectal cancer, processed meat and mortality — are largely built on FFQ data. The instrument is therefore foundational to nutritional epidemiology despite its known limitations.
Reported limitations include:
- Portion estimation error — most respondents are poor at estimating typical serving sizes
- Recall bias — respondents systematically misreport based on social desirability and recent salient meals
- Closed list constraint — foods not on the list are missed or imputed to “other”
- Calibration drift — many widely used FFQs were validated decades ago and may not reflect current food supplies
See dietary assessment for a comparison with other methods, and 24-hour recall for an alternative approach.