Chris Kresser: Well, Saccharomyces boulardii is a strain that is closely related to baker’s yeast, which is Saccharomyces cerevisiae. I think it was isolated back in the early 20th century. The most obvious difference as far as I’m aware—I’m not a microbiologist, but I’ve done a little research into this—is that Saccharomyces boulardii undergoes optimal growth and replication at body temperature, around 96 degrees Fahrenheit or 37 degrees Celsius. That’s one of the reasons it’s used as a supplement, and another reason is that it’s better able to survive the pH of the stomach. When it’s taken orally, it is better able to get through to the small intestine. So they’re closely related, but they’re not the same, and Saccharomyces boulardii is the form that is used in supplementation. Also you’ll notice that on the Doctor’s Data stool panel—and we talked about this in the treatment section—when they identify Saccharomyces, they can’t tell whether it’s boulardii or cerevisiae, and 9 times out of 10, if not 99 times out of a 100, when you see that on a stool test, it’s because the patient has been supplementing with it, so that’s always the first question that you want to ask.