Wednesday, February 05, 2014

Yet Another Good Reason to Question Observational Diet Studies

Change in self-reported intake of fruits, vegetables, sweets and soft drinks by month
Or at the very least those that utilize food frequency questionnaires (FFQs) to account for dietary intakes (which is almost all of them).

I can't say I'm an ardent fan of research done with FFQs, and nor are many others (remember this letter to the editor begging journals to stop published research that utilizes FFQs?), but supporters will tell you that the errors of FFQs can be accounted for with fudge factor style statistics. While admittedly I'm no stats maven, I did find a study published yesterday in the Journal of Nutrition Education and Behaviour to lend support to my belief these studies aren't as useful as we might hope.

The study highlighted an obvious, and yet important issue that would further undermine FFQ utility - the month the data was collected matters. While the researchers looked at FFQ outcomes collected from adolescent residents of 36 countries, there were 3 - Canada, England and Norway - where data collections took place almost all months of the year. In all 3 researchers found that there were significantly lower reported levels of daily consumption of foods in January and February. In the remaining 36 countries, where FFQs were administered for shorter periods, researchers found lower reported consumption of fruit and sugared soda in the spring vs. the fall and the winter.

Now admittedly, the effect they found here was small, and in part may be explicable on the basis of seasonal food availability, though that wouldn't serve to explain the sugared soda or sweets results. Regardless of affect size or cause however, one thing's definitely clear, FFQs need to go, and I'm praying, in this day and age of smart phone ubiquity, that someone somewhere validates an app that combines daily recall with real-time photography, to help reduce error and markedly amp up the power of observational diet-related study conclusions.

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