The Probiotics Trend: Should We Be All In or Call Time Out?

David A. Johnson, MD


November 09, 2018

Hello. I'm Dr David Johnson, professor of medicine and chief of gastroenterology at Eastern Virginia Medical School in Norfolk, Virginia.

The ingestion of dietary live bacteria supplementation, or probiotics, has become widespread in recent years. In the United States, it is estimated that approximately 4 million adults consume probiotics on a daily basis.[1] Furthermore, nearly 60% of care providers recommend probiotic supplements on a routine basis.[2]

This trend warrants further scrutiny, and three recently published studies give us more information about whether we should be all in on probiotics or call time out on their increasing use.

Is Their Effect Consistent and Durable?

The first study,[3] which comes to us from the Weizmann Institute in Rehovot, Israel, looked at the durability of the effect of these probiotics.

Researchers began by giving probiotics to germ-free mice, in which they were actually able to induce the desired microbial changes. When they gave the probiotics to mice that were already colonized with their own innate bacteria, however, there were evident resistance patterns. They were not able to induce the colonization that they thought they would when they gave the probiotic. The same effect was evident when they tested it in humans. There seems to be certain bacterial resistant patterns in hosts that either facilitate or block the colonization intended by this probiotic effect.

Probiotics are recommended for a variety of clinical reasons, including fortifying the immune system, protecting against cardiovascular or metabolic diseases, enhancing post-infectious health, and improving bowel function. But this study indicates that probiotics may not actually have these intended effects.

This raises a couple of concerns. First, when probiotics are given, it may not stick. Second, and quite interestingly, when it does stick, the effect might be quite variable in the colon. This was shown when researchers found that stool and biopsy microbiome analyses were not equivalent. In other words, there were variations across the microbiome and geographic variance within the colon where the biome would resist or enhance the colonization based on that probiotic effect.

Do They Help Post-antibiotic Recovery?

The second study,[4] which also comes from the brilliant researchers at the Weizmann Institute, looked at post-antibiotic microbiome changes in mice and humans who were given either multistrain probiotics or autologous fecal microbiome transplantation (ie, transferring the pre-antibiotic microbiome back to subjects via their earlier stool).

Researchers found that there was a rapid reconstitution of the normal biome when they gave the patients their pre-antibiotic stool back. Comparatively, the use of probiotics was associated with a marked delay in patients being able to return to what their normal microbiome was before antibiotics.

This study shows that we may want to reconsider the use of probiotics in the post-antibiotic setting, as they may actually delay the return to the normal biome. Instead, there may be existing or as-yet-undeveloped strategies that allow for reconstitution of the microbiome by targeting the individual host microbiome.

Have They Been Proven Safe?

The third study[5] deals with the safety of various strategies for modifying the microbiota. This comprehensive meta-analysis, published in the Annals of Internal Medicine, looked at approximately 340 studies, of which 245 specifically evaluated probiotics.

It was remarkable how few of these studies actually reported adverse events of harm. Nearly a third or more of all trials included reported no adverse event monitoring or harm, whereas 98% provided no adequate documentation, validation, or standardization in reporting adverse events or serious adverse events. Given the high variability in the quality of existing data, the authors concluded that it may be too premature to make any broad conclusions about the safety of these interventions.

Certainly, just like any other medication, potential harm needs to be assessed in probiotics. This is especially true given that probiotics contain a variety of additives. For example, a couple of years ago, a group of researchers from Columbia University in New York City found that of the 22 market-leading probiotics they studied, 12 contained gluten.[6] Of these 12 products, eight claimed to be "gluten free" on their labeling.

The over-the-counter industry is fairly loosely regulated, particularly as it applies to probiotics. Their additives may cause symptoms in and of themselves, and we have to remember our first rule in medicine is to do no harm. Probiotics may have some benefit in select patients, but in others there may be some harm. Particular caution should be exercised for immunosuppressed and immunocompromised patients, as well as those in the hospital with indwelling lines, in whom there have been reports of mortality and disseminated fungemias.[7,8]

When it comes to a verdict, I'd lean more toward "time out" than going "all in." Probiotics have a lot to potentially offer, but we may be better off delivering and tailoring to the individual host rather than adopting a one-size-fits-all approach.

I am Dr David Johnson. Thanks again for listening.

Follow Medscape on Facebook, Twitter, and Instagram.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.