Validity of U.S. nutritional surveillance:National Health and Nutrition Examination Survey caloric energy intake data, 1971-2010.

IMPORTANCE

Methodological limitations compromise the validity of U.S. nutritional surveillance data and the empirical foundation for formulating dietary guidelines and public health policies.

OBJECTIVES

Evaluate the validity of the National Health and Nutrition Examination Survey (NHANES) caloric intake data throughout its history, and examine trends in the validity of caloric intake estimates as the NHANES dietary measurement protocols evolved.

DESIGN

Validity of data from 28,993 men and 34,369 women, aged 20 to 74 years from NHANES I (1971-1974) through NHANES 2009-2010 was assessed by: calculating physiologically credible energy intake values as the ratio of reported energy intake (rEI) to estimated basal metabolic rate (BMR), and subtracting estimated total energy expenditure (TEE) from NHANES rEI to create 'disparity values'.

MAIN OUTCOME MEASURES

1. Physiologically credible values expressed as the ratio rEI/BMR and 2) disparity values (rEI-TEE).

RESULTS

The historical rEI/BMR values for men and women were 1.31 and 1.19, (95% CI: 1.30-1.32 and 1.18-1.20), respectively. The historical disparity values for men and women were -281 and -365 kilocalorie-per-day, (95% CI: -299, -264 and -378, -351), respectively. These results are indicative of significant under-reporting. The greatest mean disparity values were -716 kcal/day and -856 kcal/day for obese (i.e., ≥30 kg/m2) men and women, respectively.

CONCLUSIONS

Across the 39-year history of the NHANES, EI data on the majority of respondents (67.3% of women and 58.7% of men) were not physiologically plausible. Improvements in measurement protocols after NHANES II led to small decreases in underreporting, artifactual increases in rEI, but only trivial increases in validity in subsequent surveys. The confluence of these results and other methodological limitations suggest that the ability to estimate population trends in caloric intake and generate empirically supported public policy relevant to diet-health relationships from U.S. nutritional surveillance is extremely limited.