Monitoring sodium intake of the U.S. population: Impact and implications of a change in What We Eat In America, NHANES dietary data processing

Authors: Sebastian, Rhonda; Enns, Cecilia; Steinfeldt, Lois; Goldman, Joseph; Moshfegh, Alanna

Submitted to: Journal of the Academy of Nutrition and Dietetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2013
Publication Date: 7/20/2013
Citation: Sebastian, R.S., Enns, C.W., Steinfeldt, L.C., Goldman, J.D., Moshfegh, A.J. 2013. Monitoring sodium intake of the U.S. population: Impact and implications of a change in What We Eat in America, NHANES dietary data processing. Journal of the Academy of Nutrition and Dietetics. 113(7):942-949.

Interpretive Summary: Accurate monitoring of U.S. sodium intake requires familiarity with national dietary data collection and processing procedures. Both the recently renewed public health focus on sodium intake and marketplace changes to the sodium content of foods have prompted USDA’s Food Surveys Research Group (FSRG) to review multiple aspects of dietary data collection and processing related to sodium intake. One aspect of this review involved a data processing step referred to as “salt adjustment” that was performed in United States Department of Agriculture (USDA) dietary intake surveys from 1985 through 2008 as a way of accounting for respondents’ reports of using salt only occasionally or less often in home food preparation. In What We Eat In America (WWEIA), the dietary intake interview component of the National Health and Nutrition Examination Survey (NHANES), the salt content of specific foods was reduced on the basis of a question about household use of salt in cooking. For individuals whose households used salt in cooking occasionally or less often, some or all of the salt attributable to home preparation was removed from foods that typically have salt added during preparation and were obtained from the store. A number of considerations have called into question the appropriateness and value of continuing the procedure. These considerations include an increase in the purchase of fully-prepared foods to which the consumer is unlikely to add more salt in cooking and results from a study that suggest that the USDA Automated Multiple-Pass Method (AMPM) produces sodium estimates comparable to those estimated by urinary sodium when the salt adjustment procedure is not applied. This report describes (a) the basis for and the process of salt adjustment, (b) the rationale for discontinuing it, and (c) the impact and implications of its discontinuation. In addition, baseline estimates for tracking changes in sodium intakes are provided. Although nutrition analysts are the primary audience for this article, it will also be of interest to policymakers and the nutrition community in general, due to the importance of being able to knowledgeably evaluate reports concerning changes in sodium intake over time. Ultimately, the information in this report will be of benefit on a national basis, since it provides researchers with appropriate baseline estimates to use in monitoring progress toward reducing sodium intakes in the United States population, a critical public health focus.

Technical Abstract: The objective of this report is to describe (a) the basis for and implementation of a data processing step called salt adjustment that was performed on designated foods in USDA dietary intake surveys from 1985 through 2008, (b) the rationale for discontinuing the step, and (c) the impact and implications of its discontinuation. As implemented in What We Eat In America (WWEIA), the dietary intake interview component of the National Health and Nutrition Examination Survey (NHANES), salt adjustment was a post-collection data processing step that was based on the respondent’s reply to a question about the use of salt in household cooking or food preparation. It was applied only to foods likely to be home prepared, i.e., foods that (a) generally have salt added during preparation and (b) were obtained from the store. For individuals who reported that salt was used occasionally or less often in cooking or food preparation in their household, salt adjustment removed some or all of the salt attributable to home preparation. One reason for discontinuing this procedure is the increased availability of fully-prepared foods in stores, which calls into question the appropriateness of using store purchase as a proxy indicator of home food preparation. Another reason is that USDA’s Automated Multiple-Pass Method (AMPM) for the 24-hour dietary recall provides accurate sodium intake estimates without applying the salt adjustment step, as demonstrated by the AMPM Validation Study. WWEIA, NHANES 2007-2008 is the final data release to contain sodium data that were salt adjusted; the step was not applied to WWEIA, NHANES 2009-2010 data and will not be performed in future survey cycles. To provide appropriate baseline estimates for tracking the success of initiatives aimed at lowering sodium intakes, this report includes 2007-2008 mean sodium intake estimates calculated both with and without the salt adjustment processing step for individuals in 23 gender/age groups. In addition, readers are directed to the Food Survey Research Group (FSRG) Web site, where a more extensive table provides additional intakes by race/ethnicity and by income.