Dubious health products tend to fall into one of several familiar patterns. Some are invented out of whole cloth, for the purpose of marketing as the latest health craze. Others emerge out of medical pseudoscience. Perhaps the most insidious, however, are those that are based on legitimate science but are either going beyond what the science can support, and/or are exploiting premature hype. Probiotics fall into this latter category.

A recent study published in Frontiers in Medicine, “Online Information on Probiotics: Does It Match Scientific Evidence?” – quantifies this phenomenon. They assessed the accuracy, completeness, and reliability of the information found online about probiotics. Only 23% of the claims made for probiotics on the 150 websites reviewed were backed by scientific evidence. Another 20% had essentially no supportive evidence, while the rest had some evidence but not enough to justify the claims.

The only claims that were backed by evidence are for gastrointestinal symptoms, which were made by 88% of the sites. Even here, though, most sites did not give complete information, properly referencing potential side effects, which bacterial species are backed by evidence, and linking to supportive evidence. The reviewed sites also included claims for boosting the immune system and treating cancer, obesity, and respiratory disorders, for which there is insufficient or no scientific evidence.

The authors also categorized the websites by type. The most common was commercial sites, 43%, who also had the least reliable information. So the most common sites were the least reliable and most of the claims made were wrong or incomplete. This should not come as a surprise, and is consistent with other reviews of online health information.

The skinny on probiotics

Our own Mark Crislip wrote an excellent review of the state of probiotic science in 2015. His bottom line, which still applies today, was that there is reasonable evidence for the use of probiotics to prevent diarrhea resulting from antibiotic use, but not for treatment once it has occurred. The current study also adds (probably the only real update):

Cochrane reviews also support the use of probiotics in the prevention of necrotizing enterocolitis in preterm infants, but with insufficient data regarding the benefits and the potential adverse effects in the most at risk infants.

But that is about it. The use of probiotics to treat any disease or illness is not established. I did my own review to see what the latest systematic reviews are saying. This one for irritable bowel syndrome is typical:

Current evidence shows particular combinations, species or strains of probiotics are effective for overall IBS symptoms. However, it is hard to derive a definite conclusion due to high heterogeneity and unclear risk of bias of some trials. Large well-designed and rigorous trials are warranted.

The research is exploring the role of the gut microbiome in various conditions, finding some correlations, but we mostly do not yet understand the cause and effect. Clinical evidence has been either negative or preliminary. No disease treatments for probiotics have been established.

Mark notes, and I agree, that the probiotic technology is still in its infancy. He also notes that the use of stool transplants, either directly or by frozen pill, works much better than probiotics. The approach of introducing one or a few benign but often foreign bacteria into the gut microbiome may simply be a flawed approach. Giving existing ecosystems of bacteria seems to be the better approach.

Our understanding of the microbiome and the potential role of trying to alter it as a health intervention is still relatively early. We are in what I like to call the early hype phase of the science. We are discovering a lot of interesting information, with intriguing implications. But leveraging this information to improve health is proving to be horrifically complicated, and most of the early clinical trials are disappointing. With probiotics we are where using viral vectors for gene therapy was 30 years ago. It seems very promising, but the road ahead was more difficult than anticipated. Here we are three decades later and the technology is still struggling, but starting to finally make some advances.

It seems like we will still need decades of research and tinkering to appreciate the real potential of probiotics. Keep in mind, I am not saying that in 30 years or so probiotics will work, I am saying it will take that much time to understand if they will work. In the end they may turn out to be more hype than reality, with limited indications and benefits. Stool transplant technology may also eclipse probiotics for those indications for which they do offer some benefit.

Probiotics may also turn out to be surprisingly helpful, but may need to wait until they are helped by other technologies, such as genetic engineering. We won’t know until we can look back over the next few decades.

Meanwhile, the concept of probiotics is now firmly established as a marketing tool. Just like routine vitamins, superfoods, herbal products, and organics – the industry has successfully created a health halo around the term. Regardless of how the science evolves, we are likely to see probiotic products as a permanent fixture in the supplement industry.

Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.