Bifidobacterium supplementation preserves gut microbiota stability and enhances wellbeing during short-term international travel: a randomized, double-blind, placebo-controlled trial

Background Short-term international travel represents an acute environmental perturbation that can disrupt the gut microbiome and contribute to gastrointestinal, respiratory, and psychological symptoms. Probiotic supplementation has been proposed as a strategy to enhance microbiome resilience; however, its effects on both microbial dynamics and multi-domain health outcomes during travel remain incompletely understood. Methods In this randomized, double-blind, placebo-controlled trial, 40 healthy adults undertaking a 7-day trip from China to Europe were assigned to receive either a probiotic formulation containing Bifidobacterium animalis subsp. lactis B94 and Lacticaseibacillus helveticus R0052 (2 × 10 9 CFU/day) or placebo. Stool samples were collected pre-travel (Day 0) and post-travel (Day 7) for metagenomic sequencing, taxonomic profiling, and functional analysis (KEGG, COG, LEfSe, qPCR). Participants recorded daily gastrointestinal, respiratory, and systemic symptoms and completed validated questionnaires assessing anxiety (GAD-7), wellbeing (WHO-5), and sleep quality (PSQI). Results Travel was associated with a significant reduction in gut microbiota alpha diversity in the placebo group, whereas diversity was preserved in the probiotic group. Taxonomic analysis demonstrated enrichment of B. animalis subsp. lactis post-travel in the probiotic group, confirmed by qPCR. Functional analysis based on KEGG annotation revealed minimal predicted pathway-level adaptation in the placebo group despite widespread disruption across COG categories, whereas the probiotic group exhibited enrichment of predicted metabolic pathways related to amino acid, carbohydrate, energy, and vitamin metabolism. These microbiome changes were associated with improved clinical outcomes. The probiotic group showed lower gastrointestinal symptom scores (including diarrhea, bloating, and reflux), reduced respiratory symptoms (e.g., sore throat, nasal congestion), and fewer systemic complaints such as dehydration and irritability. Anxiety scores remained within the non-clinical range in both groups but were lower post-travel in the probiotic group. Wellbeing improved clinically (≥10% increase in WHO-5) in the probiotic group, and global sleep quality (PSQI) was better post-travel compared with placebo. Conclusions Probiotic supplementation during short-term travel preserves gut microbiome diversity and is associated with predicted functional adaptation of the gut microbial community, which is associated with improved gastrointestinal, respiratory, and psychological outcomes. These findings suggest that probiotic supplementation may contribute to microbiome resilience and support overall traveler health, potentially involving gut–immune and gut–brain interactions that require further mechanistic investigation. Clinical trial registration: https://clinicaltrials.gov/study/NCT07384260 , identifier: NCT07384260.