Usual Dietary Intakes: Background

Proper assessment of dietary intakes is critical in both dietary surveillance research that examines intakes relative to recommendations, and epidemiologic research that examines the relationships between diet and disease risk. Among the most frequently used methods of assessing dietary intake are the 24-hour recall and the food frequency questionnaire (FFQ). These two methods have key differences:

• 24-hour recalls ask people to report everything eaten and drunk during the previous 24 hours. They are rich in details regarding every item consumed (when, how, how much, with what), but they are expensive to administer and, if left unadjusted, represent only a "snapshot in time." That is, a single recall does not reflect a person's long-term average daily intake.
• FFQs ask about intake over an extended period. They are relatively inexpensive to administer and can capture the majority of a person's diet, but they are limited to foods on the instrument. Because of this and cognitive difficulties in recalling typical intake over a long period, FFQ reports also fail to truly reflect a person's long-term average daily intake.

The concept of long-term average daily intake, or "usual intake," is important because dietary recommendations are intended to be met over time and diet-health hypotheses are based on dietary intakes over the long term. However, until recently, sophisticated efforts to capture this concept have been limited at best.

With these facts as a starting point, we developed an improved method of assessing long-term average, or "usual," dietary intake that builds on the strengths of 24-hour recalls and can employ FFQs when applicable. This research has the potential for advancing our methodological work, and has implications for our work in food guidance and policy. An improved sense of what people really are eating will help in formulating targeted recommendations and evaluating progress toward national health objectives.