Introduction: We have shown that gut microbial diversity is associated with hypertension in the Coronary Artery Risk Development in Young Adults (CARDIA) Study. Animal models have documented gut microbial effects on adiposity, a known risk factor for hypertension. The extent to which adiposity may mediate the association between the gut microbiome and hypertension has not been studied. Hypothesis: We hypothesize that adiposity is a mediator of the association between gut microbial diversity and hypertension. Methods: We analyzed data from the CARDIA Study (480 participants). Shotgun metagenomic sequencing was performed on DNA extracted from stool samples collected at the Year 30 exam (2015-2016). Taxonomic classification of sequenced reads was performed using Kraken2. Within-person gut microbial diversity was assessed at the genus level using the Shannon Diversity Index and richness (number of distinct genera); lower values indicate less diversity. Hypertension was defined as systolic BP ≥140, diastolic BP ≥90 mm Hg, or taking antihypertensive medication. We performed mediation analyses to quantify the percentage of the total estimated effect of gut microbial diversity on hypertension that is mediated by adiposity as assessed using body mass index (BMI). Results: Mean age of the participants was 55.1 (3.4) years, 47% were African American, and 53% were female. In multivariable-adjusted mediation analysis, BMI explained on average 26-34% of the association between gut microbiota diversity and hypertension (Table). Results were robust to adjustment for sociodemographic variables (Model 2) and health behaviors (Model 3). Conclusions: Approximately one-third of the total effect of gut microbial diversity on hypertension is mediated through adiposity.