How to Prevent a Stomach Flu from Ruining Your Vacation: What to Eat the Week Before You Go, What Supplements to Take, and Why Fungi Can Help by microbiome scientist DR. EMILY LEEMING

Nothing ruins a holiday faster than getting sick with a stomach flu. One minute you’re enjoying your holiday abroad, the next minute you’re stuck in your hotel room while running.

It is very common: according to studies, up to 50 percent of people who travel abroad get a stomach flu.

And symptoms such as three or more watery bowel movements per day, stomach cramps, fever, nausea or vomiting can cause days of misery.

The most common trigger is harmful bacteria from contaminated food or water.

These bacteria produce toxins that your intestines try to flush out, causing watery stools. Some bacteria, such as salmonella, invade your intestinal lining and cause inflammation, making it harder to absorb water and nutrients, resulting in diarrhea.

Whatever the cause, symptoms usually clear up within two to three days without the need for medical attention (although if you have diarrhea that lasts for more than a week, or you have blood in your stool, it is best to see a doctor ).

But for some, travelers’ stomach becomes more than a temporary discomfort, as it can increase the risk of developing irritable bowel syndrome (IBS).

In fact, a review published in the journal Gastroenterology in 2017 found that 10 percent of people who have had a traveler’s tumor develop long-term IBS, with symptoms such as bloating, diarrhea or constipation, and abdominal pain.

This is thought to be because the infection causes inflammation in the intestines and changes the balance of bacteria there, meaning symptoms persist in the weeks and months after the infection clears.

All this underlines the merit that prevention is better than cure.

But beyond standard advice like being careful with tap water and ice (if it’s made with contaminated water) and following the “boil it, cook it, peel it or forget it” rule when it comes to fresh food, there are also other strategies to prevent traveler’s diarrhea while on vacation.

Here are my prevention tips – plus my advice on ways to quickly relieve symptoms if you do get sick, so you can get back to enjoying your holiday sooner.

BOOST GUT BACTERIA

IN THE week before your trip, remember to get your gut ‘travel ready’, by which I mean get your gut bacteria in good shape. That’s because trillions of harmless bacteria and other microbes living in your colon — collectively known as your gut microbiome — can help prevent harmful invaders from colonizing your intestines and causing infections. They do this in several ways.

A study from the University of Oxford, published last year in the journal Science, found that having a healthy gut microbiome, with many different types of gut bacteria, blocks the growth of harmful bacteria such as salmonella by using up the nutrients they need have to survive.

Your gut microbiome also interacts with your immune system: 70 percent of your immune cells live in the lining of your intestines.

And a healthy community of gut bacteria can help boost your immune system’s defenses, making it easier for your immune cells to identify and fight off harmful bacteria before they cause an infection.

The good news is that it doesn’t take long for the health of your gut microbiome to change; it may last as little as three to four days, according to a study published in 2013 in the journal Nature.

Start feeding your gut bacteria in the fortnight counting down to your holiday by focusing on eating more fiber – which good gut bacteria thrive on. Simple steps can help, such as making sure half your plate is full of vegetables at lunch and dinner, and eating nut and seed snacks.

Also try adding fermented foods to your daily diet, such as kefir (fermented dairy products), which form the basis for a great gut-friendly breakfast of wheat bran, berries, nuts and seeds.

Another fermented food to try is kimchi – a type of fermented cabbage with other vegetables – which works well as a side dish or to crisp up sandwiches.

TAKE A FIBER CAPSULE

For extra reassurance, you can also take a daily supplement of a type of fiber called galactooligosaccharide (B-GOS), which specifically feeds your ‘good’ gut bacteria.

For one study, 81 volunteers were given a daily sachet of 5.5 grams of B-GOS, which they had to take starting the week before their trip and continuing throughout their vacation. 78 received a placebo.

According to results published in 2009 in the journal Nature, those taking B-GOS were 40 percent less likely to develop traveler’s diarrhea than those taking a placebo.

In addition, those who got sick had less stomach pain and recovered in half the time of the placebo group.

It is believed that B-GOS not only feeds your ‘good’ gut bacteria, but also forms a protective barrier on the lining of your intestines, preventing harmful bacteria from sticking to the intestinal surface and causing an infection.

Similar compounds are found in soybeans, chickpeas and lentils and while it is not known whether eating these will have the same effects, they will add beneficial amounts of fiber to your diet.

Freeze the leftover vegetables

You can buy B-GOS online or at most health food stores as a powder or capsule.

While it may seem practical to use up everything in the fridge before traveling, not buying fresh, perishable produce like fruits and vegetables can be counterproductive for your gut bacteria.

Plus, it can make you more dependent on packaged, ultra-processed foods, which, if they make up a large part of your diet, can be bad news for the microbiome.

Instead, focus on fresh produce that has a long shelf life, such as root vegetables, or cook and freeze leftover food that doesn’t have a long shelf life. You can roast containers of vegetables with garlic and herbs, or use them in soup before freezing them.

WRAP SOME PACKAGES

This may sound unlikely, but yeast can help prevent and treat a stomach flu.

In addition to bacteria, the gut microbiome contains fungi, including certain yeasts, and taking a yeast capsule can help defend your immune system by boosting its numbers.

A 2019 review of studies published in the Journal of Travel Medicine and Infectious Disease found that taking the probiotic yeast Saccharomyces boulardii CNCM I-745 (available in some supermarkets or health food stores) in the days before the holidays and while you away, reduces the chance of getting a stomach flu on holiday by 20 percent.

And if you do experience diarrhea, a 2023 study published in BMC Gastroenterology found that taking Saccharomyces boulardii CNCM I-745 in addition to acetaminophen and an antispasmodic may relieve symptoms, such as stomach pain and fever, better than a placebo.

Try to take it a week before and during your holiday.

TRY A BANANA REMEDY

The biggest danger when traveler’s diarrhea strikes is dehydration. And because you’re losing not only fluid but also electrolyte salts, such as sodium, chloride and potassium, which help your body’s fluid balance, water alone may not be enough to fully hydrate you.

If you feel weak or dizzy, this may be a sign that you are low on fluids and salts. Although you can buy rehydration sachets or electrolyte drinks to help, you can make your own remedy by adding six teaspoons of sugar (to speed up the rate at which your body absorbs water) and half a teaspoon of salt (to supply sodium and chloride) a liter of water. To get extra potassium, eat a banana alongside it.

As for fluids, aim for 1.5 to 2 liters of fluid per day.

PUT OFF THE ICE

Even if you feel well enough to eat and drink normally, it’s worth being careful in the early days of your recovery until your system feels like it’s truly back to normal.

So avoid coffee as it can have a laxative effect, stimulating your intestines to pass food quickly, much like decaffeinated coffee, albeit to a lesser extent.

The same goes for spicy foods, because the capsaicin, found in spices like chili powder and paprika, can speed up the speed at which food moves through your intestines.

You may also want to postpone your holiday ice cream because your intestines cannot fully digest the lactose, the sugar in milk, when you have diarrhea, and this can make your symptoms worse.