Dietary Assessment Primer

Learn More about Direct Observation and Feeding Studies

By design, both [glossary term:] observation studies and [glossary term:] feeding studies occur in specific settings. Institutional meal settings, such as in schools, cafeterias or nursing homes, provide the optimal opportunities for unobtrusively observing study participants in natural eating environments. Trained research staff observe individuals during a meal, noting all foods and portions consumed. The observer may have access to a planned menu, weighed portions given to participants, and/or plate waste. Feeding studies are typically conducted in more controlled research environments and always include unobtrusive recording of pre- and post- meal weights of known foods. In many studies, two research staff are assigned to monitor participants' intakes. Quality control procedures for individual observers and across observers should be developed and followed. For both direct observation and controlled feeding studies, standardized recording forms should be used.

Direct observation and controlled feeding studies of dietary intakes are arduous tasks, but can be useful for assessing true intakes over short periods of time. These methods are often used in [glossary term:] validation studies to obtain reference intake estimates. For example, studies comparing direct observation of intakes to intakes reported by participants have been used to assess [glossary term:] accuracy of dietary intake reporting among children and adults. Agreement between observed and reported intakes can be examined for both foods and nutrients consumed. Direct observation and feeding studies allow for the assessment of accuracy in terms of exact matches of reported to known intakes, as well as intrusions and exclusions. Intrusions are foods reported that were not consumed, and exclusions are foods consumed and not reported.

Although observation and feeding studies are often used to collect reference data for self-reported intakes, opportunities for measurement error still exist (see Key Concepts about Measurement Error). Portions consumed may be estimated visually rather than weighed, and some foods consumed may be missed. Accurate estimation of condiments and other additions is particularly challenging.

For More Information

Baxter SD, Thompson WO, Litaker MS, Guinn CH, Frye FH, Baglio ML, Shaffer NM. Accuracy of fourth-graders' dietary recalls of school breakfast and school lunch validated with observations: in-person versus telephone interviews. J Nutr Educ Behav 2003 May-Jun;35(3):124-34. [View Abstract]

Kirkpatrick SI, Subar AF, Douglass D, Zimmerman TP, Thompson FE, Kahle LL, George SM, Dodd KW, Potischman N. Performance of the Automated Self-Administered 24-hour Recall relative to a measure of true intakes and to an interviewer-administered 24-h recall. Am J Clin Nutr 2014 Apr 30;100(1):233-240. [Epub ahead of print] [View Abstract]