I took Latin in high school and never learned French. This is my excuse for the many years that I misunderstood what the yeast Saccharomyces boulardii was. You see, Saccharomyces is the Latin word for yeast and I mistakenly thought the word boulardii had something to do with the French word, “boulangerie,” which means “bakery.” Thus I mistakenly assumed that S. boulardii was a form of baker’s yeast. But S. boulardii is not, as I thought, the type of yeast used to make French bread. Turns out this yeast is a major player when it comes to promoting overall health by supporting the health of where it all begins—the gut.

S. boulardii is actually an Asian yeast that grows on lychee and mangosteen fruits. It was named for the French scientist Henri Boulard who is credited with isolating it from these tropical fruits in 1923 after he observed people chewing the fruit skins to treat cholera. Boulard’s yeast has been used to treat various intestinal ailments ever since.

This particular strain of yeast, obviously native to the tropics, is related to but distinct from regular baker’s yeast, S. cerevisiae. S. boulardii has become popular as a nutritional supplement in recent years and, though a yeast, is still often called a probiotic. Like the beneficial acidophilus bacteria, it also maintains and restores normal flora to the small and large intestine and improves immune function.

When taken orally, S. boulardii colonizes the gut within three days of consumption. Yet it doesn’t survive long in the intestines; it will be completely gone in about five days after one stops ingesting it. In the process, though, it will crowd out other unwanted bacteria and yeast. One need not take it for long periods of time—I typically tell patients to finish a bottle and see if they feel better. More often than not, they do, especially if they have a gut infection that isn’t responding to other treatments.

There are more than three hundred scientific papers on S. boulardii. We can summarize them and say that taking this yeast as a supplement has six main effects:

1. Protects against gut pathogens
2. Moderates immune responses (prevents immune system from over-reacting)
3. Decreases inflammation
4. Inhibits bacterial toxin action
5. Enhances function of gut enzymes and nutrient transport mechanisms
6. Increases gut immunoglobulin, secretory IgA (the main antibody found in the mucous secretions of the GI tract; protects against harmful microbes)

In the past, the main uses of S. boulardii were to treat travelers’ diarrhea and antibioticcaused diarrhea and gastritis, but many studies later, more uses for S. boulardii have emerged. In just the past year, papers have been published in medical journals describing S. boulardii’s effectiveness in improving digestive function; treating amebic dysentery in children; treating Clostridium difficile infections, bacterial infections that causes diarrhea and may lead to more serious intestinal conditions such as colitis; decreasing mucositis, inflammation and ulceration of the mucous membranes lining the digestive tract, often a side effect of chemotherapy; and preventing colon cancer.

A paper published in late 2009 describes how S. boulardii inhibits the growth of Candida albicans and decreases the virulence, that is, the nastiness, of this often problematic yeast. Another paper describes S. boulardii’s anti-inflammatory effects as an explanation for why it is useful in treating inflammatory bowel disease (IBS). And yet another study suggests that S. boulardii may decrease bacterial translocation and lung injury related to pancreatitis. [fn value=1][/fn]

Another fascinating use of this yeast is that it appears to calm down hyperactive immune function. German researchers found that S. boulardii decreases the secretion of key proinflammatory cytokines (proteins secreted by cells in the immune system in response to infection) such as tumor necrosis factor-alpha and interleukin-6, while increasing antiinflammatory interleukin-10.

As I confessed, for many years, I mistakenly assumed that S. boulardii was a form of baker’s yeast. Under this misconception, I conducted an interesting experiment at home; I used S. boulardii as my yeast to bake a batch of bread. It was only while the bread was rising that I began to read up on S. boulardii and realized my error. The bread rose just fine and was edible, but still, I would not suggest you follow my example. There is no question that this yeast is under-utilized in the United States, but we should use it more often to treat intestinal issues, not to bake bread.