ObjectiveThe objective of this study was to evaluate whether long stays in non-European countries influence the composition, diversity, and dynamics of gut microbiota, considering the potential impact of travelling, close contact with new people, and consumption of water and food. MethodsTwo prospective cohorts were analyzed: (i) A longitudinal cohort comprising long-term travellers who provided fecal samples before and after their travels. (ii) A cohort consisting of long-term travellers and recently arrived migrants from non-European countries, which was compared with non-traveller controls. Each participant self-collected fecal samples and provided demographic and epidemiological data. Microbiota was characterized through 16 S rRNA gene sequencing. ResultsThe longitudinal cohort comprised 17 subjects. A trend toward higher bacterial diversity was observed after travelling (Shannon index 3.12vs3.26). When comparing 84 travellers/migrants with 97 non-travellers, a confirmed association of higher diversity levels with travelling was observed (Phylogenetic diversity: 22.1vs20.9). Specific genera enriched in travellers' gut microbiota were identified, including Escherichia/Shigella, Bacteroides, and Parabacteroides. The analysis revealed three major clusters with profound differences in their bacterial composition, which exhibited differential distribution between travellers and non-travellers (Adonis P < 0.001; R2 = 30.6 %). Two clusters were more frequently observed in travellers: The first cluster, characterized by dominance of Escherichia/Shigella, exhibited the lowest levels of richness and diversity. The second cluster, dominated by Faecalibacterium and Bacteroides, displayed the highest richness and diversity patterns. ConclusionThese findings highlight the diverse impact of international travel on gut microbiota composition and underscore the importance of considering microbiota resilience and diversity in understanding the health implications.