What does the evidence for ‘probiotics’ say?

A recent editorial in the Lancet starts with the premise that “…both commercial and clinical use of probiotics is outpacing the science.” This article came on the heels of 4 papers published during the fall of 2018, which were critical of probiotic use or demonstrated a lack of efficacy. Along with colleagues, I’ve commented on these studies.*

Is this Lancet editorial correct that probiotic use is outpacing the science?

Surely, in some cases (although I have no idea how to quantify this) people are taking probiotics that are not providing them any measurable benefit. However, this is not unique to probiotics, as it’s likely many supplements, functional foods, diets or drugs used in the hope of providing benefit do not. This likely has much to do with host factors (such as diet, health status, resident microbiota, medication intake, and host genetics), but may also have to do with lack of effectiveness. (Hence the concept of Number Needed to Treat in medicine.) We can all agree that some benefit must be demonstrated before a product should be recommended.

Clinical use of probiotics can be justified for several endpoints (see here for a review). But in some cases that evidence is, as the Lancet editorial states, mixed or of low quality. However, in a risk vs benefit analysis, clinicians and consumers may judge that use is justified. Even in cases where the quality of the evidence is low, if the risk of harm is low and if alternative clinical options are extremely limited (e.g., IBS, infant colic, symptoms from antibiotic associated diarrhea or C. difficile infection), a decision to try probiotics may make sense. Further, the probiotic user will be able to determine if a benefit was achieved and continue or stop use accordingly. Some clinical organizations have made strong recommendations for certain probiotics based on low or moderate quality evidence for this exact reason (see World Allergy Organization, European Society for Pediatric Gastroenterology, Hepatology, and Nutrition).

Of course, high quality evidence of benefit is preferred and it is likely as more high level studies are conducted the evidence level will improve.  Clinical trailists have gotten better at what they do. Hopefully more and higher quality studies will clarify which probiotics will best work for which clinical conditions for which patients.

Yes, some probiotics are being marketed with minimal evidence of efficacy. Some probiotic use may be driven more by blind faith than evidence. But there are many well-studied probiotics that are backed by convincing evidence. The problem isn’t so much that probiotic use is outpacing the science, but that use too often isn’t evidence-based. Sweeping headlines such as “Probiotics labelled ‘quite useless’” (BBC), which sensationalize and misrepresent evidence, ignore available data.

*For the studies by Suez and colleagues Cell 2018; 174: 1406–23 and Zmora and colleagues Cell 2018; 174: 1388–405, see here. For the studies by Freedman and colleagues N Engl J Med 2018; 379: 2015–26 and Schnadower and colleagues N Engl J Med 2018; 379: 2002–14, see here.