Travelan colostrum showed no clear protection from travelers' diarrhea in an 850-person trial

Travelers’ diarrhea is the classic hazard of a trip abroad, and travelers can buy supplements that promise to keep it away. One is made from cow colostrum and sold as Travelan, and it carries antibodies against a bacterium behind many cases. Products of this kind worked well on volunteers who were given a dose of that bacterium in a clinic. How well they work on real trips was uncertain.

Now one has been put to that test, and it did not clearly work. In a randomized, double-blind trial published on October 1 in eClinicalMedicine, researchers from the Infectious Disease Clinical Research Program at the Uniformed Services University in Bethesda, Maryland, tested the supplement against a placebo. Their volunteers were US and UK service members and civilians heading to high-risk regions. Diarrhea struck 22.7% of those on the supplement and 26.3% of those on placebo, a gap small enough to be chance and well short of the protection the trial was designed to detect.

What hyperimmune bovine colostrum is and how it is meant to work

Colostrum is the first milk a mammal produces after giving birth, thick with antibodies that protect the newborn’s gut. “Hyperimmune” colostrum comes from cows that have been vaccinated against particular germs so that their colostrum carries antibodies to them. In early trials the tablets were made from a colostrum extract from cattle immunized with 14 ETEC strains. ETEC stands for enterotoxigenic Escherichia coli, a type of the common gut bacterium that makes a toxin causing watery diarrhea.

The idea is that antibodies swallowed with each meal latch onto ETEC in the gut before it can settle in and cause illness. That is harder than it sounds, because the antibodies have to survive stomach acid on the way. The bacterium itself was the obvious target. A 2009 review of 51 published studies of travelers’ diarrhea found the bacterium in 30.4% of cases, the most common single cause, though its share varied widely by region.

The early evidence was striking. In two challenge trials published in 2011, 90 healthy adult volunteers took colostrum tablets or placebo and then swallowed a dose of one ETEC strain. The best regimen conferred 90.9% protection against diarrhea compared with placebo, and other doses gave between 58% and 83%. Those trials tested the tablets with and without an antacid buffer, and the colostrum extract had been chosen partly for its own resistance to acid. Yet the new trial’s authors note that despite widespread use, real-world efficacy remains uncertain.

How the military colostrum trial was run

The trial was sponsored by the Henry M. Jackson Foundation for the Advancement of Military Medicine with the Uniformed Services University and was explicitly not designed to support a marketing application for the product. It recruited adults aged 18 to 70 due to spend at least 10 days somewhere at intermediate to high risk for diarrhea. Between June 2022 and April 2025, 975 people enrolled and 850 were assigned at random, 425 to each group.

The product was Travelan, according to the trial registration, taken as one sachet twice daily with meals. Participants took 600 mg of it or a matching placebo each time, starting two days before travel and continuing for up to 20 days. Neither they nor the researchers knew who was getting which. People who had taken antibiotics in the previous week, or who planned to use other preventive products such as bismuth tablets, rifaximin or probiotics, were excluded, so the comparison was not muddied by other remedies. Participants kept a travel diary, and the trial registration counts diarrhea as 3 or more unformed stools in a 24-hour period, or two with a symptom such as nausea, vomiting, stomach pain or fever, or any antibiotic treatment for diarrhea. Stool smears taken during bouts of illness were tested for germs in the lab, so the researchers could tell how many cases ETEC actually caused.

The main analysis counted 317 people on the supplement and 323 on placebo, 640 of the 850 assigned.

How many travelers got diarrhea on colostrum and placebo

Travelers’ diarrhea was common in both groups: about one in four participants experienced travelers’ diarrhea during the trial. It occurred in 22.7% of the supplement group and 26.3% of the placebo group. Expressed as protection, the supplement cut the rate by an estimated 13.7%.

That number came with a wide margin. The true effect could plausibly lie anywhere from about 13% more diarrhea to about 34% less, so the trial cannot rule out that the supplement does nothing at all. Before starting, the researchers had set a bar of at least 35% protection, and the estimate came in below the protocol-specified efficacy threshold. Fixing the bar in advance matters, because it stops anyone from deciding after the fact that a small difference was the effect they had hoped for. The trial was also built as a superiority trial, designed to show that the supplement beat placebo by a meaningful margin. A product that worked as well as the challenge studies suggested would have cleared that bar easily. This one did not come close.

The supplement did not seem to soften the illness either. According to the university, it did not lessen the severity of diarrhea in those who fell ill.

The results for ETEC itself were less clear-cut. The bacterium was behind 12.1% of the supplement group’s diarrhea cases and 21.5% of the placebo group’s, a difference in the expected direction. But ETEC accounted for 17% of the diarrhea cases with an identified cause, too few to show whether that gap was real, and the authors describe the ETEC-specific result as constrained by limited power.

On safety the news was good. Adverse events were rare and mild: two people in each group reported one. In the supplement group these were frequent urination and hives, and both went away on their own.

Why colostrum worked in challenge studies and not on the road

A challenge study and a real trip test different things. In the clinic, volunteers swallow one known strain at a known dose, chosen to match the antibodies in the product, and the researchers know exactly when the exposure happened. In the 2011 trials that was a single strain from one serogroup, the same family the cows had been immunized against. Abroad, travelers meet whatever is in the food and water, and in this trial the samples showed frequent multi-organism detections, meaning many people with diarrhea carried more than one germ at once.

The target bacterium was also a smaller share of the problem than older studies suggested. In this trial it caused about one case in six with a known cause, against roughly three in ten in the 2009 global review. A product aimed squarely at ETEC cannot do much against the other five in six.

“One major issue is that ETEC HBC targets certain ETEC strains, while TD can be caused by a broader range of ETEC strains, co-infections or other diarrheal pathogens,” said Tahaniyat Lalani, the study’s first author. HBC is short for hyperimmune bovine colostrum and TD for travelers’ diarrhea. The paper ends by calling for products with wider antibody coverage, or ones aimed at several germs at once, to deal with the pathogen diversity and polymicrobial infections that travelers actually meet.

Where the colostrum result leaves travelers

Travelers’ diarrhea is usually a short illness, but it is not trivial. Acute diarrhea is the most common illness that affects travelers to low-income regions, according to a 2015 review in JAMA. That review put the risk for a two-week stay at between 8% and 20% in some parts of the world and found that the illness causes 12% to 46% of travelers to change their travel plans. It also noted that a lasting bowel problem, post-infectious irritable bowel syndrome, may occur in 3% to 17% of patients afterward. On antibiotics taken in advance, the reviewers wrote that chemoprophylaxis should be restricted to travelers who are at risk of severe complications.

The same review found that prevention by dietary avoidance measures is often not successful, which helps explain the appeal of a supplement. A 2017 expert-panel guideline on prevention and treatment counted David Tribble, the new trial’s last author, among its authors. It found strong evidence for treating most moderate to severe cases with antibiotics and said that fluids alone, loperamide or bismuth subsalicylate may suffice for most cases of mild diarrhea. The panel also listed changing the gut’s bacterial community, for prevention as well as treatment, among the questions that need further study. Which measures fit a particular trip and traveler is assessed by a travel health clinician.

Tribble framed the result as a test of a whole category of supplements. “Nutraceutical products are widely used by travelers with the assumption of benefit yet lack high-quality evidence to support their effectiveness,” Tribble said.

Limits of the colostrum trial

The trial tested one product at one dose, taken for 10 to 20 days by military personnel and civilians heading to high-risk areas. Results might differ for longer stays, different destinations or a different formulation. Whether a higher dose, or a colostrum raised against many more strains and germs, would do better is the question the authors leave for the next trial.

Only 640 of the 850 people assigned were in the main analysis. If those left out differed between the two groups, that could tilt the comparison either way.

Because its target bacterium caused so few cases, the trial could not settle whether the supplement protects against that germ specifically. It shows what matters to a traveler: against travelers’ diarrhea as a whole, there was no clear benefit.