International travel disrupts gut health through dietary changes, microbial exposure, and stress, often causing gastrointestinal symptoms like traveler's diarrhea and sleep disturbances. These shifts may increase antibiotic resistance risks. Probiotics may help stabilize gut microbiota and improve well-being during travel. This randomized, double-blind, placebo-controlled trial investigated whether probiotic supplementation mitigates gut microbiota perturbations, gastrointestinal symptoms, and sleep issues in adults traveling abroad. The investigators also assessed changes in anxiety, well-being, gut immunity, microbial function, and antibiotic resistance genes.

International travel exposes individuals to abrupt changes in diet, water sources, microbial exposures, sleep schedules, and psychological stress. These factors often perturb the gut microbiota and influence host health outcomes. Studies have reported significant fluctuations in gut microbiota among travelers, even in those without diarrheal symptoms, with marked shifts in microbiome composition during short-term travel. Such perturbations are frequently accompanied by gastrointestinal symptoms and reduced well-being, highlighting the need for strategies to maintain gut homeostasis during travel.

Traveler's diarrhea remains one of the most common travel-related illnesses, with incidence rates varying from 30-70% depending on destination and season. Gastrointestinal discomfort during travel extends beyond diarrhea to include abdominal pain, abnormal gut transit, loose stools, and other non-diarrheal symptoms. These issues can significantly impact travel comfort and enjoyment.

International travel has also been associated with increased risk of acquiring antimicrobial-resistant organisms and genes, posing concerns for both individual and public health. The gut environment facilitates the selection and exchange of antibiotic resistance determinants, with studies showing increased abundance and diversity of antimicrobial resistance genes following travel.

Sleep disturbances represent another significant challenge during travel, arising from time zone changes and adaptation to new environments. These disruptions can profoundly affect well-being given sleep's critical role in health. The relationship between sleep and gut microbiota through the microbiome-gut-brain axis suggests that sleep disturbances during travel may contribute to gastrointestinal vulnerability through neuroendocrine, immune, and metabolic pathways.

Probiotics, defined as live microorganisms that confer health benefits when administered in adequate amounts, represent a potential intervention strategy. Evidence suggests probiotics enhance colonization resistance against pathogens, modulate immune responses, strengthen epithelial barrier integrity, and generate beneficial metabolites. Beyond gastrointestinal benefits, probiotics may influence systemic inflammation, lipid metabolism, and mental health outcomes through the gut-brain axis. While some evidence supports their role in reducing gastrointestinal transit time and constipation symptoms, as well as modest protection against traveler's diarrhea, robust data specifically regarding travel-related probiotic interventions remains limited.

The investigators conducted a randomized, double-blind, placebo-controlled trial in healthy adults undertaking short-term international travel. The study aimed to determine whether daily probiotic supplementation attenuates travel-associated perturbations in gut microbiota composition and diversity, while assessing concurrent changes in gastrointestinal symptoms, sleep quality, anxiety, and subjective well-being using validated instruments. Functional outcomes included assessment of specific microbial species, secretory immunoglobulin A, vitamin-related indices, antibiotic resistance genes, and metabolic pathway analyses to provide mechanistic insights. The investigators hypothesized that probiotic supplementation would stabilize the gut microbiota, enrich beneficial taxa and functions, and improve both gastrointestinal comfort and psychological outcomes compared with placebo.

Inclusion Criteria:

• Generally healthy adults
• Scheduled to undertake a short-term round trip (less than 7 days) to abroad
• Able to complete study procedures
• Willing to take intervention products

Exclusion Criteria:

• Use of antibiotics, probiotics, hormones, immunosuppressants, biologics or JAK inhibitors within four weeks prior to study
• Chronic or severe systemic diseases (including cardiovascular, hepatic, renal, malignant or psychiatric disorders)
• Uncontrolled parasitic infections
• Long-term use of corticosteroids, growth hormone, vitamin B12, lysine or inositol
• Major surgery within one month
• Allergy to probiotic components
• Other conditions deemed inappropriate by investigators