October 29, 2018

Are probiotics the 'key to good health'—or an under-researched gimmick?

Daily Briefing

     Editor's note: This popular story from the Daily Briefing's archives was republished on Sept. 6, 2019.

    Marketers of products such as yogurts and dietary supplements commonly tout probiotics as a "key to good health," but research shows for most conditions, probiotics are ineffective and may even be harmful, Aaron Carroll writes for the New York Times' "The Upshot."

    Cheat sheets: Evidence-based medicine 101

    How the probiotic hype has gotten ahead of the research

    When it comes to probiotics, "there's still a lot we don't know," Carroll writes.

    Probiotics are simply strains of living microorganisms that are purportedly beneficial for "gut health," Carroll writes. Probiotics are sold in the form of supplements, beauty products, and foods, such as yogurt and sauerkraut.

    But while marketers have hyped probiotics, the research to date is not promising, according to Carroll.

    Earlier this year, Nutrition "published a systematic review of systematic reviews" on the efficacy of probiotics in treating gastrointestinal disorders. The review confirmed that probiotics can treat some gastrointestinal disorders, but only "for very specific uses of very specific strains of bacteria in very specific instances," Carroll writes.    

    For instance, Carroll writes, the review found that certain strains of bacteria were useful in preventing diarrhea in children who were taking antibiotics. A 2013 review suggested probiotics help prevent Clostridium difficile-associated diarrhea in patients taking antibiotics, while other evidence exists suggesting probiotics could help prevent necrotizing enterocolitis and preterm infant deaths.

    But those "are just about all the 'positive' results you can find," Carroll writes. Researchers have tested but have not found significant benefits of probiotic supplements for people with chronic diarrhea, Crohn's disease, eczema, gestational diabetes, liver disease, ulcerative colitis, and urinary tract infections.  

    According to Pieter Cohen, an associate professor of medicine at Harvard Medical School, some individual study results "suggest [the] strains work, but when a larger more well-done study is performed, they no longer seem to," which Carroll said confirms "that we don't have the data to show that [probiotics] work."

    Carroll writes, "When research is done on probiotics, it usually involves a specific organism, defined by genus, species and even strain." But he added, "When we buy probiotics off the shelf, especially when they are in food products, we often have no idea what we're getting."

    That's largely because FDA does not vet probiotics sold in stories, according to Cohen. "They're not carefully watching over the probiotic space, leaving consumers to be the guinea pigs for these science experiments," Cohen said.

    Is it time to ditch probiotics?

    Despite inadequate research, almost four million Americans used probiotics in 2012, and the global market for probiotics exceeded $32 billion in 2014, Carroll writes.

    While probiotics can have benefits under very specific circumstances, Carroll says that, when it comes to drugs and supplements, consumers should proceed with caution.

    "Of course, people with no immune deficiencies should feel free to eat yogurt and sauerkraut, which can absolutely be part of a healthy diet," Carroll writes—but "eat them because they're delicious, and most likely better for you than many other foods, not because of any health claims" (Carroll, "The Upshot," New York Times, 10/22).

    Learn more about why study design matters

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