EAT THEIR WORDS: On Our Ability to Compare National Intake to the Dietary Guidelines for Americans

Abstract

This paper examines our current ability to measure the extent to which the national diet aligns with the Dietary Guidelines for Americans (DGA). For the past three and a half decades, the data used to assess this correlation has been drawn primarily from the National Health and Nutrition Examination Survey (NHANES). However, investigations into the 24- hr dietary recall, the backbone of the survey’s collection procedure, have shown the propensity of this method to induce underreporting of energy intake. Underreporting is especially prevalent in overweight and obese individuals, and to a lesser extent women. Because together these groups comprise the bulk of the American population, this paper argues that NHANES is not a valid metric for comparing population intake to the DGA. The central analysis first replicates and then expands upon a 2013 study by Archer, Hand, and Blair which found that a majority of the reported energy intakes from NHANES were implausible based on the predicted basal metabolic rates of the sample. The expansion incorporates updates to NHANES 24-hr recall methodology, and in doing so addresses the primary criticism of Archer and colleagues’ study. Its results support the theory that NHANES cannot be used to assess how American diets comply with the Guidelines due to a high incidence of gender- and body mass index-dependent underreporting, which is thought to vary across food and macronutrient categories and thus likely distorts dietary patterns. As NHANES has been the main tool for comparing national intake to the DGA, the fact that this paper’s findings undermine its validity necessitates the conclusion that this relationship is as of yet unknown. Further research is needed to develop a politically and economically feasible method for estimating the dietary intake of a population which is predominantly overweight and obese. Until this occurs, policymakers would be well advised to cast a critical eye towards current measurements and instead focus on understanding the forces which push the national diet towards and away from government dietary advice, and to consider the ethical implications of issuing nutritional recommendations when both the evidentiary basis and the ability to measure their impact is questionable.