There’s no single ideal method for assessing diet in research studies. The National Cancer Institute provides some helpful guidance on the pros and cons of different dietary assessment methods.
Let’s start with the Food Frequency Questionnaire — a questionnaire aimed at understanding the frequency and amount of consumption of different foods and beverages over a specified period of time. Usually, the questions are worded to assess consumption over the last month or year. So it’s a tool for getting at general diet characteristics for an individual or population group.
Next, there’s the 24-hour recall. In contrast to the FFQ, which aims to get at general characteristics, the 24HR tries to get at detailed and specific information, usually through a structured interview with a trained researcher to elicit every single food and beverage consumed in the last 24 hours. Researchers are usually trained to ask very specific questions, e.g., if coffee is consumed, they would probably ask “did you add cream and sugar?”, “how much cream?”, and “how much sugar?”.
A third type of tool is the screener. Screeners are usually designed to be short questionnaires (self-administered or given by an interviewer) that focus on a relatively small number of key food or beverage items, or food practices. The example that NCI provides as a question in a food screener is: “Do you generally butter your bread?”. They also suggest that screeners be limited, so that they take no more than 15 minutes to complete.
Fourth, is the food diary or food record. A diary is typically a self-report tool, in which the study participant keeps a record of the foods and beverages they consume. Usually, this type of tool is adminstered over a period of consecutive days (e.g., the 3-day food diary). Rather than providing a list of specific questions about specific food and beverage items, usually the diary is open-ended, allowing study participants to list whatever it is they consume.
In deciding which tool is more appropriate for a study, there are many factors to consider. Accuracy and precision of the dietary assessment is certainly important. But feasibility and practicality are also very important because some of the assessments can be very time consuming for study participants — and the more time-consuming a method is, the greater the chance that people won’t comply with the method, mis-report, or alter their diets. However, methods that rely on trained interviewers can be logistically difficult due to time and cost or needed research staff, and participant burden in scheduling and conducting interviews.
There’s much more to consider, and NCI offers a “dietary assessment primer”, which is very useful for planning appropriate assessment methods for a new study.
Read more on NCI website.