ABSTRACT. Haitians comprise one of the fastest growing subgroups of immigrants in the US. These immigrants experience high levels of psychological distress (i.e., depression, anxiety, fatigue, and pain), contributing to progressive functional impairment, disability, economic burden, and poor long-term health outcomes. Knowledge of factors contributing to psychological distress early in the post-migration period and longitudinally will help inform type and timing of interventions to reduce the disabling effects of psychological distress and improve quality of life for this underserved population. Yet no studies have examined psychological distress and its underlying biobehavioral, psychosocial, and cultural characteristics in Haitian immigrants within the first few months of residence in the US or over time. While multiple biological processes may be associated with psychological distress, rising evidence suggests that gut microbiome (GM) diversity and composition play an important role via the bidirectional microbiome-gut-brain axis. After migration, changes in GM composition and diversity embody changes in the social determinants of health ([SDoH]; e.g., stress, sociodemographic factors, lifestyle behaviors, dietary patterns, acculturation, environmental and sociocultural conditions) that also contribute to risk for psychological distress. With more time in the US, the GM of recent immigrants becomes more Westernized, with reductions of microbial phylogenetic diversity and native GM species as well as genera-level shifts in microbiota abundance. The SDoH that drive these GM changes are modifiable through culturally responsive interventions. The GM thus has the potential to serve as both an early indicator of risk for psychological distress and a tool to mitigate its effects. The overall goal for this longitudinal pilot cohort study is to investigate associations between psychological distress, GM composition/diversity, and post-migration SDoH in recent Haitian immigrants to the US. Specific aims are to 1) Characterize the GM in 60 recent Haitian immigrants by analyzing self-collected stool samples at T1 (< 6 months in the US) and T2 (6 months after T1) and describe changes in composition/diversity over time and 2) Examine longitudinal associations between post-migration SDoH, GM composition/diversity, and psychological distress among recent Haitian immigrants. I hypothesize that, in recent Haitian immigrants, a) migration to the US is associated with changes in GM composition and diversity over time, and b) changes in GM composition and diversity are associated with changes in post-migration SDoH and psychological distress. The PI has assembled an interdisciplinary mentoring team of senior scientists with expertise in symptom science, GM, biocultural approaches, immigrant health disparities, genomics, and bioinformatics. This project will provide the foundation for the PI to build an independent translational research program focused on developi...