What are the indications for use, benefits, and potential side effects of Brewer's yeast? Is it safe for use during breast-feeding? Is it safe for children?

Brewer's yeast, also known as baker's yeast, Faex medicinalis, levure de bière, and medicinal yeast, is included in a class of probiotics or biotherapeutic agents defined as "live microbial supplements", which beneficially affect a host by improving its natural microbial balance. Brewer's yeast is produced as a byproduct of beer-brewing, using an extract of grains and hops. Other agents in the probiotic class include lactobacilli (found in some natural "live" yogurts) and lactic-acid-producing enterococci. Scientific names for yeast include Saccharomyces boulardii and S cerevisiae (family: Saccharomycetaceae).

Brewer's yeast is available as a supplement in a number of commercial preparations. It is increasingly being included in fermented milks and food products and can also be designated a "nutraceutical." Dosage varies from 1 gram per day to 6 grams daily (orally), depending on indications for use.  For example, the typical dose for preventing diarrhea is 250-500 mg 2-4 times a day. The dose for treatment of recurrent diarrhea is 1 gram daily for 4 weeks. In Crohn's disease, the recommended dose can be as high as 250 mg 3 times a day for 9 weeks.

The most common use for Brewer's yeast has been for antibiotic-associated diarrhea (AAD), traveler's diarrhea, rotavirus diarrhea in children, infectious diarrhea such as amebiasis, and general digestive problems including irritable bowel syndrome, lactose intolerance, relapsing Clostridium difficile colitis, and bacterial overgrowth in short bowel syndrome. Evidence for possible effectiveness in diarrhea is more robust for AAD and prevention of relapse of C difficile colitis when used with pharmacologic agents (metronidazole or vancomycin) than for other gastrointestinal indications. Fewer data are available for its other uses, including vaginal Candida albicans yeast infections, high cholesterol levels, premenstrual syndrome, furunculosis, and adolescent acne. It is considered "likely ineffective" for gastrointestinal colonization by C albicans in patients with cystic fibrosis.

The mechanism of action of S boulardii and S cerevisiae is believed to be mediated by increased activity of intestinal disaccharidases, saccharidases, maltase, and lactase to reduce diarrhea. S boulardii typically reaches a maximum steady state within 3 days when taken orally and does not multiply in the gut. Less than 1% is recovered from the stools. In C difficile diarrhea, S boulardii may act by producing proteases that reduce the toxicity of toxins A and B.

The argument for using probiotics for treating AAD and other forms of diarrhea rests on cost-effectiveness and lack of or fewer side effects, compared with other alternative pharmacologic treatments.

The S boulardii and S cerevisiae contained in Brewer's yeast have been demonstrated in multiple clinical studies to be more effective than placebo when used in conjunction with medications for treating AAD, except in elderly patients. The effectiveness for other indications is still questionable, and larger controlled trials are needed.

Brewer's yeast is considered "likely safe" when used orally in adults and "possibly safe" when used orally in children. Insufficient reliable data are available for pregnant and lactating women, and use in this group should be avoided. Adverse reactions include migraine-like headaches, intestinal discomfort and flatulence, hypersensitivity reactions such as urticaria, itching, local or general exanthemas, and Quincke's edema. Use with monoamine oxidase inhibitors (MAOIs) is contraindicated and can cause uncontrolled hypertension. Use in Crohn's disease and HIV-associated diarrhea, other inflammatory bowel disease, and in immunocompromised individuals is cautioned because of the possible risk of fungemia. Concomitant use of antifungals can cause S boulardii to be ineffective.

Desiree Lie, MD, MSEd. "Use of Brewer's Yeast" Posted: 10/31/2003 on Medscape Family Medicine: http://www.medscape.com/viewarticle/463265