TABLE 1.

Comparison of diet assessment methods

	Several day/week diet records	Multiple 24-h recalls	A single 24-h recall	Validated FFQ	Biomarkers
Advantages	Provides accurate, detailed, open-ended data on dietary intake, with no reliance on memory, and direct computation of portion sizes.	Provides fairly accurate, detailed, open-ended data on dietary intake, without reliance on long-term memory.	Provides detailed, open-ended data on dietary intake, without reliance on long-term memory.	Provides time-integrated data that represents usual long-term intake. Can assess past dietary intake.	Provides an objective assessment of intake. Represents bioavailable dose, which is relevant when it is used in etiologic analyses.
	Errors from omission, portion size estimation, and recall are least likely.	Has lower respondent burden and is less expensive than diet records, and works well in low-literacy contexts.	Has lower respondent burden and is less expensive than diet records and multiple recalls; works in low-literacy contexts.	The least expensive and most easily administered diet assessment method, with the lowest respondent burden.	May be available in retrospect (analysis of stored specimens).
Disadvantages	Needs literate, motivated participants; participant burden is very high when done over several days. Could also alter usual eating habits.	There is scope for short-term recall error, omissions, and errors in portion size estimation.	There is scope for short-term recall error, omissions, and errors in portion size estimation. Has high random within-person error.	There is scope for long-term recall error. Omissions possible because of fixed-food list. FFQs need to be culture- and population-specific.	Biomarker may not be sensitive to intake, may have low specificity, may not be time-integrated, may not represent usual long-term intake, and is subject to laboratory errors and other sources of bias.
	Expensive and resource-intensive diet assessment method. Potential for errors in nutrient estimation from food composition tables.	Has high interviewer burden and is more expensive than a single recall and FFQs. Potential for errors in nutrient estimation from food composition tables.	Has high interviewer burden and is more expensive than FFQs. Potential for errors in nutrient estimation from food composition tables.	Semi-quantitative. Potential for errors in nutrient estimation from food composition tables.	Expensive and more invasive. Biomarkers are not available for many nutrients.
Applications	Validation of other diet assessment methods.	Validation of other diet assessment methods.	National surveillance of mean population intake.	Association analyses in large epidemiologic studies.	Validation of other diet assessment methods.
	Monitoring compliance in dietary intervention trials.	Monitoring compliance in dietary intervention trials.	Assessment of trends in dietary intake (earlier NHANES).	Assessing past dietary intake.	Association analyses in epidemiologic studies and monitoring compliance in intervention trials
		Assessment of trends in dietary intake (current NHANES).