Who can go to Naples without indulging in pizza? To Jamaica without eating the spicy jerk chicken, or to Mexico without eating the local enchiladas?

Part of the joy of summer travel is the new culinary experiences, of course. But what are the consequences of adopting a diet that’s so different from your everyday eating habits?

From the evidence to date, it seems drastic dietary changes can be a big deal to the bacteria and other microorganisms that live in your gut. Picture what could be happening: your community of gut bacteria is busy doing all the jobs it normally does in your body, including the production of vitamins, and of short-chain fatty acids that act as energy sources for intestinal cells. But suddenly, its supply chain completely changes.

Some scientists have referred to the gut microbiome as the body’s “interface with the external world of the traveler.”

Research from Harvard several years ago was the first clear demonstration that the human gut microbiome responded within 24 hours to a drastic dietary shift—in this case, switching from a diet of mostly animal products to one of mostly plant products. The animal-based diet prompted a rapid decrease in microorganisms (Roseburia, Eubacterium rectale and Ruminococcus bromii) that break down dietary fibre from plants.

As for the effects of travel itself, few human studies exist. But some scientists have referred to the gut microbiome as the body’s “interface with the external world of the traveler”, since the measured species of gut microorganisms may change based on diet and other factors surrounding travel.

Research from 2015 showed what happened when mice mimicked global travel and its accompanying dietary changes. In the study, researchers harvested the gut microbiota of people from different countries, each with a typically different diet: one person from Bangladesh, one from Malawi, one from Venezuela, and two from the USA (one with a typical US diet and another with a protein-rich and fat-rich “primal” diet). Germ-free mice were transplanted with these human microbiota samples and then, as if the mice were on a global tour, they were fed a sequence of diets that represented each different place. The researchers were surprised to learn that these mix-and-match combinations of diet and existing gut microbiota affected gut transit time: the length of time it took for food to move through the digestive tract. Other research shows close links between gut bacteria and motility, but here, these links depended on the diet the mice were consuming at the time.

More study is needed before we know exactly how the temporary gut microbe rearrangements induced by travel could impact human health. It’s true that traveling to some areas of the world carries an increased risk of contracting infectious diseases, including those that involve diarrhea—but the role of the gut microbiota in these illnesses requires further investigation.

So of course, take advantage of the local offerings on your summer voyages. But according to the scientists, just don’t think the critters in your gut are unaware of your weakness for Canadian poutine.



David LA, Maurice CF, Carmody RN, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014; 505: 559–563.

Dey N, Wagner VE, Blanton LV, et al. Regulators of Gut Motility Revealed by a Gnotobiotic Model of Diet-Microbiome Interactions Related to Travel. Cell. 2015; 163: 95-107.

Riddle MS, & Connor BA. The traveling microbiome. Current Infectious Disease Reports. 2016; 18(9): 29.