Abstract BACKGROUND: A growing body of research supports associations between the gut microbiome and colorectal cancer (CRC) development. Although screening and treatment have reduced overall CRC mortality and incidence rates, racial disparities remain. Non-Hispanic Black individuals experience higher CRC incidence and mortality compared to other racial groups. Dietary intake is a key determinant of gut microbiome composition and often varies by race. These race-associated dietary patterns may contribute to differences in the gut microbiome, suggesting that CRC racial disparities could potentially be mediated by diet-induced microbial differences. The association between the widely endorsed Dietary Approach to Stop Hypertension (DASH) diet and its effects on gut microbiota remains poorly understood. The purpose of this ongoing feeding study is to examine the impact of the DASH diet on gut microbiota compared to the Standard American diet (SAD) among a sample of racially diverse adults. METHODS: The full trial will enroll 112 generally healthy, cancer-free, non-Hispanic Black and White adult men and women residing in the Tampa Bay Area for a nutritional intervention study. After completing a 1-week run-in on the standard American diet, participants are randomized to receive either DASH or SAD for 4 weeks. Herein, we describe progress and baseline data for the first 50 participants. Fecal samples were collected weekly from participants during the 7-week intervention period. Fecal DNA was extracted by the Moffitt Tissue Core and shipped to UAB Microbiome Core for 16S rRNA sequencing to characterize gut microbiome composition. Microbial diversity (alpha diversity, beta diversity) was analyzed with Quantitative Insights into Microbial Ecology (QIIME, version 2). RESULTS: Mean participant age and body mass index (BMI) were 37 ± 11.5 years and 26 ± 6.9 kg/m2, respectively. Majority of participants were women (58%) and 82% were White. Alpha diversity was similar between races at baseline (H=0.41; p=0.51). No significant pre-intervention racial differences were observed in beta diversity using unweighted UniFrac distances (pseudo-F =1.02; p=0.39). Following the intervention period, we expect to see a trend towards increased alpha diversity and beta diversity in both racial groups. CONCLUSION: Preliminary analyses indicate no racial differences in key aspects of the gut microbiome at baseline. Thus, we are well positioned to detect any effect modification by race when evaluating any intervention effects. In this ongoing study, the diversity of the cohort is critical for exploring the intersection of dietary patterns, cancer risk, and health disparities. Our next steps will focus on expanding outreach to underrepresented populations to ensure racial balance in the final sample enrolled and randomized. Additional research is needed to establish the effectiveness of the DASH diet as a strategy for cancer risk reduction. Citation Format: Kiana Antoine, Vivian Doerr, Emily Rozen, Alissa Pena, Tiffany L. Carson. A feeding study examining the effects of diet-specific interventions on the gut microbiome and colorectal cancer risk factors among a racially diverse sample abstract. In: Proceedings of the 18th AACR Conference on the Science of Cancer Health Disparities; 2025 Sep 18-21; Baltimore, MD. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2025;34(9 Suppl):Abstract nr À153.
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