A Food Frequency Questionnaire (FFQ) is a standard tool used to measure food frequency by assessing an individual's usual dietary patterns over a defined period, typically a month or a year. Unlike a food diary, which captures current intake, an FFQ is retrospective. This makes FFQs valuable for large-scale studies where daily logs are impractical.
The Anatomy of a Food Frequency Questionnaire
An FFQ primarily consists of a list of foods or food groups and options to indicate consumption frequency. They can be self-administered or interviewer-led. Key components include food items, frequency categories, and sometimes portion sizes.
Food Items and Groups
FFQs use a fixed list of foods tailored to the target population, ranging from dozens to hundreds of items.
Frequency Categories
Respondents select from categories like "daily," "weekly," "monthly," or "rarely/never" for each food item to describe their usual intake frequency.
Portion Size
Some FFQs are semi-quantitative, including questions about portion size to improve nutrient intake estimates, often using standard sizes or visual aids. Others are non-quantitative, focusing only on frequency.
Example: An FFQ in Practice
A semi-quantitative FFQ might ask about the frequency of consuming different types of fish over the past year, as seen in studies like EPIC. A table could present fish types with frequency options:
| Food Item | Never/Rarely | 1-3 per month | 1-2 per week | 3-4 per week | 5+ per week |
|---|---|---|---|---|---|
| Oily fish (salmon, mackerel) | ☐ | ☐ | ☐ | ☐ | ☐ |
| White fish (cod, haddock) | ☐ | ☐ | ☐ | ☐ | ☐ |
| Shellfish (prawns, mussels) | ☐ | ☐ | ☐ | ☐ | ☐ |
| Fried fish in batter | ☐ | ☐ | ☐ | ☐ | ☐ |
By selecting the appropriate box, respondents provide data that researchers can link to nutritional databases to estimate nutrient intake, such as omega-3 fatty acids, within the study population.
Advantages and Limitations of FFQs
FFQs offer benefits but also have limitations.
Advantages
- Cost-Effective for Large Groups: They are less expensive and time-consuming for large populations compared to methods like 24-hour recalls.
- Captures Habitual Intake: Designed to assess long-term dietary patterns.
- Good for Infrequent Foods: Effective at capturing foods eaten occasionally.
Limitations
- Fixed Food List Issues: May not capture all dietary items or evolving eating habits.
- Recall and Social Desirability Bias: Relies on memory, which can lead to errors, and participants may alter responses.
- Inaccurate Portion Size: Estimating portion sizes can be challenging and inaccurate.
Food Frequency vs. Food Diaries
Comparing FFQs to food diaries helps clarify their roles. Food diaries record intake in real-time over a few days, reducing recall bias but increasing participant burden.
| Feature | Food Frequency Questionnaire (FFQ) | Food Diary |
|---|---|---|
| Recall Period | Retrospective (e.g., last month or year) | Prospective (real-time recording) |
| Best For | Assessing long-term, habitual diet patterns | Capturing detailed, short-term intake |
| Participant Burden | Low | High |
| Cost | Low (especially self-administered) | Higher (requires more data processing) |
| Portion Size Accuracy | Often estimated and can be inaccurate | Potentially more accurate (can be weighed) |
| Major Bias | Recall bias, social desirability bias | Changes in eating habits due to recording |
The Role of FFQs in Research
Despite limitations, FFQs are crucial in nutritional epidemiology for studying the link between diet and disease. They allow researchers to rank individuals by intake levels, aiding in understanding health outcomes. Valid FFQs are vital, often validated against more detailed methods. The National Cancer Institute offers resources like the Diet History Questionnaire (DHQ).
Conclusion
An example of food frequency is exemplified by the Food Frequency Questionnaire (FFQ), a tool providing valuable insights into typical dietary intake. By recording consumption frequency for specific foods over time, FFQs offer a practical method to study diet-health relationships in large groups. Despite limitations in precision and recall, the FFQ's ability to capture long-term patterns makes it a vital tool in nutritional research and public health.
