Limitations in the assessment of dietary energy intake by self-report.

Development of the doubly-labeled water method has made it possible to test the validity of dietary intake instruments for the measurement of energy intake. Comparisons of measured energy expenditure with energy intake from either weighed or estimated dietary records against energy expenditure have indicated that obese subjects, female endurance athletes, and adolescents underestimate habitual and actual energy intake. Individual underestimates of 50% are not uncommon. Even in non-obese adults, where bias is minimal, the standard deviation for individual errors in energy intake approaches 20%. Two investigations of the validity of self-reported dietary records for measuring change in dietary intake also indicate large underestimates of the actual change. Because of bias and imprecision, self-reported energy intakes should be interpreted with caution unless independent methods of assessing their validity are included in the experimental design.