Dietary Supplement GI Support Gluten Free Saccharomyces boulardii is a yeast species that can provide substantial support to the health of the gastrointestinal tract. In clinical studies, Saccharomyces boulardii has been demonstrated to increase the production of secretory IgA, the first-line defense immunoglobin of the gastrointestinal tract. This beneficial yeast also may be effective for occasional diarrhea.