Travel is meant to transport you far from the same-old, same-old. But when you’re not eating the same foods and sleeping on the same schedule (or even in the same time zone), the ripple effects on digestion can be fierce.

With more nerve cells than many parts of the central nervous system, including the spinal cord, our gut knows when we’re off our routine, says Dr. Kyle Staller, a gastroenterologist at Harvard-affiliated Massachusetts General Hospital. “Our bodies, including our gastrointestinal tract, respond to circadian rhythms — day-and-night cues,” he says. “Your colon will sleep when you sleep and wake up when you do. If those times are shifted by travel and changing time zones, digestion can get thrown off.”

Factor in heavy meals, too much alcohol, or dehydration from flying, and “it’s sort of a perfect storm to cause digestive problems,” Dr. Staller says. “Even the stress of travel itself can trigger them.” The result? Diarrhea, constipation, and indigestion — the trifecta of travelers’ tummy troubles — can potentially derail your trip.

Foodborne dangers

Travel took a hiatus during the pandemic, but today’s packed airplanes, rental car shortages, and booked-solid hotels signal a turnaround. According to U.S. Travel Association predictions, pent-up demand will fuel a surge over the next few years in all types of travel, including to destinations across the globe.

Far-off locales, however — especially in developing countries — pose the biggest threat of delivering an unpleasant souvenir dubbed traveler’s diarrhea. Its abdominal cramps and loose stools stem from eating or drinking germ-laden foods and beverages. Traveler’s diarrhea affects an estimated 30% to 70% of travelers, according to the CDC. It can occur anywhere, but the highest-risk destinations are in most of Asia, the Middle East, Africa, Mexico, and Central and South America.

The condition typically results from poor hygienic practices in food handling and preparation or a lack of refrigeration. You’re also more likely to get it if you’re an older adult or — as with traveler’s tummy in general — if you already have a digestive problem, such as irritable bowel syndrome, that changes how you eat or eliminate food.

Microbes aren’t the only culprit. “Some people get so-called adjustment diarrhea, when they haven’t ingested anything that’s infectious but they’re adjusting to new foods or spices,” Dr. Staller says.

Keep digestion humming

The first step in warding off traveler’s tummy is to learn from past mistakes, especially if you’re prone to digestive upsets. “The tendency is to arrive somewhere new and embrace it in all aspects,” Dr. Staller says. “Instead, keep your food choices more in line with things you eat at home, drink plenty of water, and eat moderate portions.”

Beyond that, Dr. Staller offers additional strategies to keep indigestion, diarrhea, and constipation at bay:

Plan ahead.

Scope out restaurants and menus beforehand to make sure at least one item seems both palatable and easy to digest. “This is more difficult, though, if you’re more of a spontaneous traveler or staying in someone’s home,” he says.

Assemble a “control kit.

” Rather than scrambling to purchase remedies in unfamiliar locations, bring along a variety of over-the-counter products to counteract digestive woes on the road. Good choices include antacids (such as Tums) for heartburn; bismuth subsalicylate (Pepto-Bismol, Kaopectate) for indigestion or diarrhea; docusate sodium (Colace, Surfak), psyllium (Metamucil), or bisacodyl (Dulcolax) for constipation; and loperamide (Imodium) for diarrhea. But don’t use loperamide if you also have signs of infection such as fever or blood in your stool, Dr. Staller says. Instead, see a doctor.

Pack familiar snacks.

Whether that’s granola bars, nuts, trail mix, or dried fruit, these items should be filling. “There’s no one-size-fits-all recommendation, but pick things you might eat at home as a quick snack or even a meal substitute in case you notice that everything at your location is going to disagree with you,” he says.

Eat street food with caution.

Local delicacies or food truck cuisine are more apt to contain harmful bacteria, especially in developing regions. “This isn’t fun, because some of the tastiest food is street food,” Dr. Staller says. “But if you indulge, know you’re taking that risk. If you’re easily derailed by digestive issues, street food is a no-go.”

Skip local water and ice.

“In the developing world, assume the water isn’t safe unless it’s from a bottle,” he says. Instead, drink only what comes in cans or bottles.

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