Whether for business or for pleasure, traveling has become a ubiquitous experience for the vast majority of individuals. However, when we travel, not everyone may be keenly aware that along with things like their luggage and travel documents, each individual carries their delicate microbiome with them into new environments. It should go without saying that traveling constitutes several challenges to both the microbiome and its associated host. Exposure to pathogens through respiratory droplets, water, and food is commonplace. Moreover, as is often the case, stress, dehydration, sleeplessness, and physical strain can all be common features of the travel experience. This constellation of challenges is why it is extremely common for individuals to experience negative symptoms within the first few days of traveling. In particular, traveler’s diarrhea is perhaps the most well understood to be directly related to the microbiome; however, as our research and understanding of the microbiome continue to evolve, many other symptoms may also be implicated. For instance, fatigue, headache, and respiratory infections are all now understood to be influenced by the microbiome.1 Given this information, it seems pertinent to review some of the natural strategies for balancing, supporting, protecting, and reinvigorating the microbiome prior to, during, and after travel.
A COMPLEX BARRIER
(The Physiology of the Gastrointestinal System’s Protective Features)
The human gut has the largest surface area to exposure ratio with 300m2 of surface area (or about the size of a tennis court)2. While this robust surface area is functionally what permits the absorption of nutrition, it also creates a unique type of shielding from pathogenic diseases. While stomach acid and bile work to sterilize and break down digested food, it is hardly 100% effective at that endeavor. That said, the bilayered protection of the gut works to make up for anything that gets through this initial defense. The external layer of the gut’s shielding is the traditional microbiome. This consists of the complex mixture of microbial species that are commonly found in the lumen of the gastrointestinal tract. Bacteria, protozoa, and intrabacterial viruses all work to establish an adaptive ecosystem that is commensal with the host. The microbiome, in effect, is the first shield of the small and large intestines. Meanwhile, the second layer of this environment consists of the cells interfacing with these gut guests. Chiefly, these are stem cells, absorptive enterocytes, mucus-secreting goblet cells, enteroendocrine cells, and Paneth cells3. This intrinsic layer of the gastrointestinal system constitutes an extremely dynamic group of cell types that turn over every few days. This creates a unique and delicate fulcrum between cell proliferation and cell death that may also play a role in the development of disease when disturbed. In health, this layer is the functional interface between the microbiome and the host's innate and adaptive immune system. It creates antibacterial peptides, samples the contents of the lumen and extrinsic microbiome, and absorbs nutrients and fluids into the cardiovascular system4.
Here, it becomes evident that such a highly metabolically active site of the body, with multiple key players from microbes to enterocytes, has many areas where challenges can result in symptoms for the weary traveler. The most common being traveler’s diarrhea. While most cases are self-limiting, there is a growing concern about chronic conditions such as irritable bowel syndrome, functional dyspepsia, or even flares in auto-immune gastrointestinal disorders being elucidated in the literature. While the exact mechanisms of this disorder are not concretely understood, there are two primary concerns that have emerged in research. The first being a disordering of the transit time of the gastrointestinal system. Diarrhea and constipation, both of which can occur with travel and are linked to dysbiosis, proceed to create a suboptimal environment for reestablishing the original healthy microbiome. The second concern is dysbiosis can erode bacterial pattern recognition receptors in the gastrointestinal tract, making the body react to healthy species it once welcomed5. This is accomplished through the translocation of luminal antigens, including ones from healthy microbes, across the intestinal barrier. In some individuals, this leaky gut scenario is resulting in chronic gastrointestinal disease secondary to an acute infection while traveling6.
INTERVENING ON BEHALF OF MICROBES
While the established complex nature of the microbiome and its responses to challenges may seem daunting at first, it also presents multiple entry points for protecting and treating the microbiome. The most researched of these approaches is unsurprisingly the administration of probiotics. One study of 245 travelers to various destinations using Lactobacillus GG probiotics had a protective efficacy of 47% in preventing gastrointestinal symptoms and diarrhea.7
Additionally, prebiotics are also being studied specifically for aiding travelers. In a double-blind placebo-controlled trial of a galacto-oligosaccharide mixture in 159 healthy travelers to countries of low and high risk for traveler’s diarrhea showed a significant reduction in diarrhea in the prebiotic group compared to those who consumed placebo (maltodextrin)8.
For as complex as the microbiome is to human health, so too are the complex workings of botanicals to support healthy gastrointestinal function as well as promote a healthy microbiome. One herb that is often overlooked for treating the gastrointestinal system is bitter melon (Momordica charantia). It is most commonly associated with promoting healthy blood sugars; however, some studies have also looked at its influence on the microbiome. In one in vivo study, not only did bitter melon affect blood sugars in rats, but it was also found to have a marked decrease in endotoxin-producing opportunistic pathogens and increased butyrate producers9. This early evidence is especially useful since it is one of the first studies to demonstrate an herb's effects on both biomarkers as well as interstitial flora.
Another herbal constituent, berberine, has been studied for its ability to improve the biodiversity of the microbiome. In a trial of 68 patients, berberine was given 200mg of berberine three times a day and both inflammatory markers such as IL-8, IL-6, and TNF-Alpha were reduced and stool specimens found after 3 months that improvements in the diversity of healthy strains of flora10.
It is no surprise that dietary approaches will play a role in rebalancing the microbiome. There have been several studies looking at different dietary approaches and which is optimal for rebalancing the gut. A trial of the Mediterranean diet found in 82 healthy overweight and obese individuals that diet led to increased levels of the fibre-degrading Faecalibacterium prausnitzii and of genes for microbial carbohydrate degradation linked to butyrate metabolism11. Another study of a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) reduces gut symptoms in quiescent inflammatory bowel disease. However, it also found notable reductions in Bifidobacterium adolescentis and Bifidobacterium longum12. These strains are both associated with a decrease in immune function as well as playing a role in mood and the gut-brain axis13.
Lastly, a study using “the gut makeover protocol” found positive results in digestive comfort, weight loss, mood, and energy levels which consisted of the following14:
- Eating three main meals per day, no snacks between.
- Undergoing a 12-hour overnight fast between dinner and breakfast, with just water permitted between.
- Eat seven American cupfuls of plants (uncooked volume) per day (five as vegetables, two as fruit).
- Eat protein with each meal (either animal, fish, eggs, nuts, or seeds).
- Eat between 20 and 30 different types of plants (fresh herbs, vegetables, and fruits) over the course of a week for variety.
- Use extra virgin olive oil and coconut oil as their default cooking oils.
- Chew food thoroughly–aiming for approximately 20 chews per mouthful.
- And does not count or restrict calories.
While the evidence is reflective of the direct impact the diet has on our microbiome, the approaches are not uniform. What appears to be uniform however is that fasting or caloric restriction coupled with high fiber whole foods coupled with mindful eating practices are the throughline of dietary interventions. Moreover, the exclusion of smoking, alcohol, and fried foods continues to be relevant for maintaining a healthy microbiome.
Travel is one of the most amazing aspects of modern living, but with it comes its own challenges. In particular, the ever-reacting microbiome can easily be knocked off balance through the immunological onslaught that comes with new foods, new environments, and disruptions to daily routine. By being mindful of the foods we eat, and utilizing prebiotics, probiotics, and herbal supports, we can stay in balance and enjoy the ride.
 Chunxi, L., Haiyue, L., Yanxia, L., Jianbing, P., & Jin, S. (2020). The Gut Microbiota and Respiratory Diseases: New Evidence. Journal of immunology research, 2020, 2340670.
 Helander HF, Fandriks L. Surface area of the digestive tract - revisited. Scand J Gastroenterol. 2014;49(6):681–9.
 Hooper LV, Littman DR, Macpherson AJ. Interactions between the microbiota and the immune system. Science. 2012;336(6086):1268– 73.
 Riddle, M. S., & Connor, B. A. (2016). The Traveling Microbiome. Current infectious disease reports, 18(9), 29.
 Verdu, E. F., & Riddle, M. S. (2012). Chronic gastrointestinal consequences of acute infectious diarrhea: evolving concepts in epidemiology and pathogenesis. The American journal of gastroenterology, 107(7), 981–989.
 Shen L , Turner JR . Role of epithelial cells in initiation and propagation of
intestinal inflammation. Eliminating the static: tight junction dynamics
exposed . Am J Physiol Gastrointest Liver Physiol 2006 ; 290 : G577 – 82 .
 Hilton E, Kolakowski P, Singer C, Smith M. Efficacy of lactobacillus
GG as a diarrheal preventive in travelers. J Travel Med. 1997;4(1):
 Drakoularakou A, Tzortzis G, Rastall RA, Gibson GR. A doubleblind, placebo-controlled, randomized human study assessing the
capacity of a novel galacto-oligosaccharide mixture in reducing travelers’ diarrhea. Eur J Clin Nutr. 2010;64(2):146–52.
 Bai, J., Zhu, Y., & Dong, Y. (2016). Response of gut microbiota and inflammatory status to bitter melon (Momordica charantia L.) in high fat diet induced obese rats. Journal of ethnopharmacology, 194, 717–726.
 Li, J., Meng, P., Zhang, J., & He, M. (2022). Effect of Berberine Hydrochloride on the Diversity of Intestinal Flora in Parkinson's Disease Patients. Contrast media & molecular imaging, 2022, 8381870.
 Meslier, V., Laiola, M., Roager, H. M., De Filippis, F., Roume, H., Quinquis, B., Giacco, R., Mennella, I., Ferracane, R., Pons, N., Pasolli, E., Rivellese, A., Dragsted, L. O., Vitaglione, P., Ehrlich, S. D., & Ercolini, D. (2020). Mediterranean diet intervention in overweight and obese subjects lowers plasma cholesterol and causes changes in the gut microbiome and metabolome independently of energy intake. Gut, 69(7), 1258–1268.
 Cox, S. R., Lindsay, J. O., Fromentin, S., Stagg, A. J., McCarthy, N. E., Galleron, N., Ibraim, S. B., Roume, H., Levenez, F., Pons, N., Maziers, N., Lomer, M. C., Ehrlich, S. D., Irving, P. M., & Whelan, K. (2020). Effects of Low FODMAP Diet on Symptoms, Fecal Microbiome, and Markers of Inflammation in Patients With Quiescent Inflammatory Bowel Disease in a Randomized Trial. Gastroenterology, 158(1), 176–188.e7.
 Duranti, S., Ruiz, L., Lugli, G.A. et al. Bifidobacterium adolescentis as a key member of the human gut microbiota in the production of GABA. Sci Rep 10, 14112 (2020).
 Lawrence, K., & Hyde, J. (2017). Microbiome restoration diet improves digestion, cognition and physical and emotional wellbeing. PloS one, 12(6), e0179017