The influence of survey duration on estimates of food intakes--relevance for food-based dietary guidelines.

Development of food-based dietary guidelines relies on correct identification and interpretation of current dietary intake patterns. The process involves assessing which foods discriminate between those with desirable and undesirable intakes of particular nutrients. It is therefore important that those involved in this task are aware of any source of variability in the underlying food consumption data that cannot be attributed to true differences between individuals. A short survey duration can introduce a high degree of within-person variation and not reflect usual or more long-term food or nutrient intakes. As survey duration increases, the % consumers identified by a survey increases and the intakes among consumers only decrease while the total population intakes do not change. A short survey duration may also lead to misclassification of individuals into high and low consumers. Survey duration is therefore an issue that should be considered in the interpretation of dietary data when developing food-based dietary guidelines.