There isn't enough scientific evidence to support using probiotics to treat most digestive disorders, according to a new American Gastroenterological Association (AGA) guideline.

Probiotics are living, microscopic organisms found in foods or dietary supplements, according to the AGA. They include certain bacteria and yeasts.

An estimated 3.9 million American adults have taken probiotics and many do so to improve their digestive health, so the AGA reviewed published research on their use for digestive disorders.

The review found insufficient evidence to recommend probiotics for treatment of Crohn's disease, ulcerative colitis, irritable bowel syndrome (IBS) and C. difficile infection, the AGA reported June 9 in the journal Gastroenterology.

"Patients taking probiotics for Crohn's, ulcerative colitis or IBS should consider stopping," said Dr. Grace Su, a professor of gastroenterology at the University of Michigan in Ann Arbor, who led the guideline panel. "The supplements can be costly and there isn't enough evidence to prove a benefit or confirm lack of harm. Talk with your doctor."

The new AGA guideline also recommends against the use of probiotics to treat acute infectious gastroenteritis in children.

The guideline does support the use of certain probiotic formulations in three situations: prevention of C. difficile infection in adults and children taking antibiotics; prevention of necrotizing enterocolitis in preterm, low birth weight infants; and management of pouchitis, a complication of inflammatory bowel disease.

"While our guideline does highlight a few use cases for probiotics, it more importantly underscores that the public's assumptions about the benefits of probiotics are not well-founded, and that there is also a major variation in results based on the formulation of the probiotic product," Su said in an AGA news release.

The AGA said well-designed clinical trials are needed to refine probiotics guidelines and investigate other relevant clinical conditions.

The association said gastroenterologists should suggest probiotics to their patients only if there is clear benefit. They should keep in mind that the effects of probiotics apply to specific strains of bacteria and combinations of strains, the AGA added.