Probiotics and Diarrhea: A Cause or a Treatment?

Although people can get probiotics through food or supplements, more research is needed to truly understand their benefits and risks. Probiotics are live microorganisms, and the idea is that it's beneficial to add good bacteria to your digestive tract. But can probiotics cause gastrointestinal issues like diarrhea?

Adding bacteria to your digestive tract might sound like it has the potential to move things along more quickly, but is diarrhea a sign probiotics are working? "The short answer is no," says Peter J. Mannon, MD, MPH, professor and chief of gastroenterology and hepatology at University of Nebraska Medical Center in Omaha. "Probiotics do not cause diarrhea. There might be an extremely rare case of probiotics that cause an intestinal infection in someone with a very weak immune system, but diarrhea is not a side effect of probiotics."

An infection from a probiotic bacteria is called an opportunistic infection, and according to the Office of Dietary Supplements (ODS), reports of these infections are extremely rare, especially when you consider how many people around the world take probiotics. The only common side effect reported is some mild intestinal gas.

Although probiotics have a long history of safety, there have been few studies that actually looked at possible harms, according to the National Center for Complementary and Integrative Health (NCCIH). If harm does occur, it is likely to be in people who are seriously ill or have a very weak immune system.

If you think you may have troublesome symptoms, like diarrhea, from taking probiotics, call your doctor. They can help you think about dosing and strains and what conditions probiotics may or may not improve, according to the ODS.

There have been lots of studies on probiotics, but not many answers. "The evidence for taking probiotics is not robust. Probiotic supplements are still unregulated. You don't really know how much you are getting. You don't even know if the bacteria are really alive," Dr. Mannon says. "There is enough evidence from animal studies to keep looking for benefits in humans, but we are not there yet."

Probiotics may help your body maintain a healthy balance between the various microorganisms that live in your digestive tract, according to the NCCIH. They make up what's called your microbiome. A healthy and balanced microbiome may strengthen your immune system. Probiotics may be able to reestablish a healthy microbiome disturbed by disease.

However, we still have a lot to learn about which probiotics and how much are helpful and safe, according to the NCCIH. Talk to your doctor before you start taking probiotics.

According to both the ODS and the NCCIH, lots of research has been done to see if probiotics can treat or prevent diarrhea caused by taking antibiotics. They have also been studied as a treatment or prevention for traveler's diarrhea and diarrhea from chemotherapy. Some studies show moderate benefits, but others have been inconclusive. Probiotics have also been studied for other digestive diseases like irritable bowel syndrome, diverticulosis and inflammatory bowel disease. Results of these studies have been inconclusive.

The medical community has not established specific recommendations on probiotics. Your doctor can help advise you on strains and doses suitable for your particular health conditions and concerns based on the human studies where benefits have been found.

Many people take a probiotic to have regular bowel movements or to prevent constipation. According to the NCCIH, a review of studies on this topic found probiotics showed some evidence of benefit in adults, including in older adults. In children, one review of studies did not show any benefit, but another found increased frequency of bowel movements.

"Probiotics may yet turn out to have benefits for people, but prebiotics may be the better bet because prebiotics promote your own healthy microbiome," Dr. Mannon says.

Probiotics are mainly bacteria from fermented foods that can be taken in those foods or as supplements, according to the ODS. The Academy of Nutrition and Dietetics lists some common probiotic foods as:

• Yogurt
• Kefir
• Kimchi
• Sauerkraut
• Miso
• Tempeh

In contrast, prebiotics are carbohydrates (sugars) that microorganisms already in your gastrointestinal tract can use for fuel, according to the ODS. The Academy of Nutrition and Dietetics lists some examples of prebiotic foods as:

• Bananas
• Onions
• Garlic
• Beans
• Whole grains