Abstract P141: Usual Impact of Vegetable and Red Meat Intake on Urinary Nitrate

Abstract

The purpose of this study is twofold: 1) compare the effectiveness of non-quantitative food frequency questionnaire (NFFQ) to one-time or multiple 24-hr recalls on assessing the associations of vegetable and meat intakes with urinary nitrate; 2) to determine the associations of vegetable and meat intakes with urinary nitrate. Nitrate-related metabolic pathways have emerged as a fascinating topic because promising benefits of using nitrate supplement on several cardiovascular related outcomes in animal and small-scaled human intervention studies. In the past, most people consider that processed meat is the main source of nitrate exposure and nitrate is harmful. In fact, the major exogenous nitrate exposure comes from vegetables. Thus, we seek to untangle the mystery vegetable-nitrate and meat-nitrate associations in a large observational study. We conduct a cross-sectional analysis using the National Health and Nutrition Examination Survey (NHANES) during 2005-2006, among 7,683 participants. Urinary nitrate was measured, NFFQ and two-time 24-hr recalls were collected among these participants. We have found a positive association between vegetable intakes and urinary nitrate and an inverse association between red meat and processed meat intakes and urinary nitrate by using either non-quantitative NFFQ or averaged two-time 24-hr recalls. The magnitudes of the results were stronger when using NFFQ. Further, using NFFQ, we found that urinary nitrate intake increased by 26%, and decreased by 16% when comparing persons with the highest to the lowest quintile of vegetable intake and red and processed meat intake, respectively. Lastly, we found that the results from the 24-hr recall collected a few days after urine collection (but not the 24-hr recall on the day of urine collection) are consistent with NFFQ results. The trend of vegetable-urinary nitrate and red meat-urinary nitrate associations from NFFQ and averaged 24-hr recalls were consistent with our previous published findings using plasma nitrate measurement in the Health Professionals Follow-up Study, where only semi-quantitative FFQ (SFFQ) was administered. In summary, we conclude that dietary assessment with NFFQ,SFFQ, or average 24-hr recalls will yield similar results when evaluating red meat-circulating nitrate or vegetable-circulating nitrate associations. Measurement of circulating nitrate using either urine or plasma will yield similar results. Understanding how usual vegetable and red meat intake influences circulating nitrate in observational studies will provide valuable information for studying nitrate related pathways in the etiology of chronic disease and for designing long-term dietary intervention studies targeting circulating nitrate.