Traveler’s diarrhea is characterized by diarrhea or constipation, abdominal pain and other gastrointestinal disorders that are experienced upon being attacked by foreign bacteria in an unfamiliar environment. Traveler’s diarrhea affects 5-50% of people, depending on their destination.
A summary of 12 double-blind, placebo controlled studies shows that probiotics are a promising preventive treatment for traveler’s diarrhea. A combination of Saccharomyces boulardii and two probiotic bacteria – Lactobacillus acidophilus and Bifidobacterium bifidum – has been shown to be very effective.  Incidence of traveler’s diarrhea in the groups using S.Boulardi was 5-11%.  
To date the most extensive study on the positive effects of Saccharomyces on traveler’s diarrhea has been carried out by Kollaritsch et al. The main conclusion – probiotics are an effective preventive treatment. If used approximately one week prior to travelling, they can reduce the risk of contracting traveler’s diarrhea. One study involved 1231 Austrian tourists travelling to exotic destination. They took a dose (250 or 500 mg) of S.boulardii or a placebo over a course of three weeks. The tourists began the course of probiotics 5 days prior to travelling and continued it throughout the holiday. Traveler’s diarrhea was experienced by 43% of the placebo group, but incidence was significantly less in the 250 mg S.boulardii dose group (34%) and the 500 mg group (32%). Another study by Kollaritsch et al involving 1016 Austrians travelling to Northern Africa, the Middle and the Far East, subjects were given 250 mg/d (5 × 109) S. boulardii, 1000 mg/d (2 × 1010) S. boulardii or a placebo, and they began taking the doses 5 days prior to travelling. S.boulardii significantly reduced the number of tourists who experienced traveler’s diarrhea: 39% of the placebo group, but only 34% of the 250 mg S. Boulardii group and 29% or 500 mg S. Boulardii group were afflicted (P < 0.05).
- McFarland LV. Meta-analysis of probiotics for the prevention of traveler’s diarrhea. Travel Med Infect Dis. 2007 Mar;5(2):97-105. Epub 2005 Dec 5.
- Kollaritsch H, Kremsner P, Wiedermann , G , Scheiner O. Prevention of traveller’s diarrhea: comparison of different non-antibiotic preparations. Travel Med Internatl. 1989;7:9–18.
- Kollaritsch H, Holst H, Grobara P, Wiedermann G. [Prevention of traveler’s diarrhea with Saccharomyces boulardii. Results of a placebo controlled double-blind study] Fortschr Med. 1993;111:152–156