Stephen Daniells, Ph.D., the food science reporter for NutraIngredients.com, wrote an excellent article today entitled Time to Ditch the FFQ that should be read by all scientists doing nutritional research (and all readers of this blog).
The premise of his piece is that the FFQ (Food Frequency Questionnaire) should be abandoned in favor of the 24 hour dietary recall or the three day food diary as a means for compiling nutritional research.
As Dr. Daniells points out, a food frequency questionnaire, a set of forms that
may contain up to 100 questions, and ask people to remember what they ate up to a year before.
And he asks the question:
Pause for a moment to reflect on what you ate last Tuesday, and on Monday 12th December.
Did you drink a small quantity of fizzy drink, a medium quantity or a large one? My small is half-a-glass. How small is your small?
So was that a small amount of fizzy drink you drank in December, or a large amount?
See the problem?
In some cases, in what are called case-controlled studies, people may be asked what they ate 10 or even 20 years before.
If they are inherently inaccurate, why are FFQs even used at all?
Because they are cheap compared to the other alternatives.
It has been estimated that a basic assessment of diet for 160 000 women would cost $1.2m using an FFQ, but over $23m for either of the two alternatives.
But, as the old saying goes, you get what you pay for. If you want to publish a paper and not spend a lot of money, then the FFQ is your tool. If you’re striving for accuracy and producing meaningful research, then you need to choose another method.
As Dr. Daniells points out
It is better to spend $20m on a study that shows something real, than $1.2m on a study that will mislead and may even harm.
I’ve always distrusted studies using FFQ’s as their means of accumulating data: now, after reading Dr. Daniells’ article, I distrust them just a little more.