There are many methods that can be used to assess dietary intake – for example, using a 24hr recall or a food diary. (In a previous article we discussed the strengths and limitations of a food diary). Choosing the correct dietary assessment method can be difficult. That’s why, we’ve created a series of articles, that discuss different dietary assessment methods that will hopefully help you choose the right dietary analysis tool for you. In this article, we explain what food frequency questionnaires (FFQs) are and their strengths and limitations in practice.
What is a food frequency questionnaire?
Food frequency questionnaires are a retrospective method that allow researchers to obtain information on an individual’s food intake over a specific period of time. FFQs contain a list of foods or food groups and the participant is asked to report on how often each of the items on the list is eaten, i.e. the frequency of consumption. Typically the format for an FFQ would be some form of tick box questionnaire, where the food item is down the left side and time period of consumption would be along the top.
An example of a question displayed in a FFQ could be:
‘How often, on average in the past month have you had chicken or other poultry? The answer options could be: Never or less than once a month/1-3 per month/once a week/2-4 per week etc.’
This information can then be coded into nutritional analysis software, like myfood24, to determine an estimation of nutrients.
When creating an FFQ it’s important to consider the list of foods/food groups included to ensure accuracy and that habitual intake is captured. Researchers can include between 20-200 food items and should include:
- all foods that are a major source of the nutrient of interest
- foods that capture variations in dietary patterns e.g. vegetarian/vegan
- foods that are commonly consumed and appropriate for the population e.g. foods included for a baby would be very different to an adult
Why are FFQs useful?
Research in large-scale populations
Food frequency questionnaires can be easily administered, particularly for a large-scale population. They can either be delivered face to face or given virtually via an online questionnaire meaning they don’t require a trained interviewer – all of which helps to keep the research costs low.
Given the nature of an FFQ they are reasonably quick for the participant to complete – reducing the participant burden compared to some other dietary assessment methods, this also helps to increase response rates.
It’s for these reasons, among others, that FFQs are most commonly used when researching a large-scale population, in particular when examining the relationship between dietary intake and disease risk. An example could be, measuring the consumption of fruit & vegetables on a weekly basis in a given population. Some of the well-known, large cohort studies that have used FFQs include The European Prospective Investigation into Cancer and Nutrition (EPIC) and The Whitehall II study.
Capturing habitual intake or specific nutrients of interest
Given that the list of food items on an FFQ can be tailored for each research study, they can help researchers investigate specific nutrients of interest by only asking about foods containing that nutrient. On the other hand, they can also contain a vast range of food items to capture habitual intake, particularly items which may not be consumed on a daily basis which could be missed using other forms of dietary assessments looking at intake on specific days.
Strengths and limitations of food frequency questionnaires
There are many strengths to using an FFQ. For example –
- FFQs capture dietary intake consumed over a long period of time (usually up to one year), this way, the researcher is obtaining long-term and habitual intake from the participant.
- A large food list can be included. This allows researchers to capture a wide variety of information on dietary intake, whilst reducing the chance of participants forgetting food items.
- The response rate of FFQs are high as it can be quick and easy for the participant to fill out and trained interviewers are not required.
- FFQs can be done online or in person. This gives the researcher flexibility when conducting research.
On the other hand, there are also some limitations to FFQs that must be mentioned.
- As FFQs usually correspond to foods consumed in the previous year, this can be difficult for the participant, as they may forget what or how often they have consumed a certain food.
- As there is a set list of foods/food groups named in a FFQ, not all foods may be captured if not presented on list. More specifically, in regards to the growing interest in pre-prepared meals and takeaways, it may be difficult for the participant to report as only basic foods are typically mentioned.
- Some FFQs ask for a portion size (small, medium or large) but it may be difficult for the participant to determine the correct portion size.
- Little detail is collected on the characteristics of foods, for example the cooking method or combinations of food in meals.
In order to carry out a FFQs, resources required include a trained coder and nutritional analysis software. A review of 227 studies using an FFQ found that steps to be taken to improve design include having a interviewer administered and a larger number of food items included may help results.
Are you interested in using myfood24?
A practical, accurate and efficient way of assessing dietary intake can be achieved using myfood24. When using myfood24, participants can self-complete their food diary using their phone, computer or tablet. myfood24 automatically calculates the nutritional value of the food diary completed by the participant, allowing the researcher to interpret the results when needed.
Get in touch to find out more or to arrange a free demonstration!
Still unsure which is the right dietary assessment method for you?
You can also visit Nutritools – a resource developed to support dietary assessment – who have released ‘Best Practice Guidelines’ to help researchers decide the most appropriate dietary assessment tool for their research.