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Probiotics: The Good, the Bad, The Unknown, and the Crazy

Microbiology is on a roll, it’s been an amazing couple decades of discoveries that have transformed our understanding of the roles that microbes play in human health.  And this knowledge has pushed its way into popular culture.  Every couple of days I see another popular media article about the influence of microbes on something else; obesity, intelligence, arthritis, allergies, height, etc.   Nowhere is this more prominent than the concept of probiotics.   For example, check out this Ngram from Google showing the use of the word “probiotic” over time:

However, the gap between the science of probiotics and the claims made by people buying and selling them seems to be getting bigger all the time.  In the interests of full disclosure, here is my personal opinion on probiotics… from which point of view I’m writing this article.

I think that the general concept of probiotics is pretty much beyond reasonable dispute.  It’s very well-established that our bodies are host to a vast and complex ecosystem of microbes that are essential to our well-being.   When we perturb this ecosystem (e.g. through the use of antibiotics) we can become susceptible to microbes that would have otherwise been kept at bay.  So the idea of ingesting a collection of beneficial microbes on purpose, for example after a course of antibiotics, makes perfect sense.  However, there are some major, major caveats.  The first and foremost of these is that we don’t really know what microbes we should be taking, and in what proportions.  Studies of the human microbiome have revealed dozens of common bacterial species in the gut and we have only the very roughest idea of what any of that might mean.  Furthermore, there are significant uncertainties in terms of things like individual variability (what’s good for me might be bad for you), delivery (how many actually make it to where they’re needed), amount (is there enough microbes in a probiotic to make a difference).  So I personally view probiotics as a perfectly scientifically sound concept whose time for widespread application has not yet come.

Photos from Wikipedia Commons; Dezzawong

So that pretty much covers the good and the unknown from my title.   What about the bad and the crazy?  When I think of the bad side to probiotics I’m not really talking about the risks (though people have in fact died, to my knowledge these have always been extreme/special cases).  What I’m talking about is the claims of the multi-billion dollar probiotic industry.   Without a lot of evidence, probiotics have been suggested as the cure for almost any condition imaginable, ranging from autism to erectile dysfunction to depression.  There have actually been a number of clinical trials on probiotics, some of which have certainly found encouraging results.   But most have been inconclusive, and no clinical trials have taken place for many of the conditions which are touted as candidates for commercial probiotics.  I am very skeptical of any industry that takes so much money from consumers in return for products which I would term at best hypotheses.

And last but not least the crazy.  This article, called “8 unusual uses for probiotics” is what prompted this post in the first place.  The article is by a company called OptiBac probiotics which has a website filled with a wealth of information on their probiotics.   To their credit they do actually cite some literature and seem to avoid some of the more outrageous claims I’ve seen.  But they do have plenty of unsubstantiated information as well as some demonstrably false statements (e.g. “All species of Actinobacteria are aerobic which means they do not require oxygen for growth”).  Anyway, this article lists 8 unusual uses for probiotics (actually 7 since there is no #4), some of which I feel comfortable calling crazy:

1. A Probiotically Clean Home

I’m pretty sure that probiotic cleaning products can’t even be called “probiotic” in the first place.  The generally accepted definition of a probiotic is “live micro-organisms which, when administered in adequate amounts, confer a health benefit on the host”.  Ignoring the semantics it’s not at all clear what is actually in these things or what the mechanism of action is supposed to be.

2. Probiotic Lotions and Potions

This talks about probiotics in skincare, specifically to reduce signs of aging.  My favorite is the Greek Yogurt facemask with added probiotics which “invigorates your skin leaving it with a lovely glow”.  No idea what the mechanism of action here is supposed to be either.

3. “Poop Soup” for Plants

This isn’t crazy at all, it’s talking about using manure tea to improve plant health/growth.  People have been doing some form of this for a very long time to good effect.

4. First Aid Bacteria

Putting a probiotic directly on a wound to “ward off pathogenic bacteria, as well as aid in reducing inflammation and aiding the healing process.”.  While I can see this in a hypothetical sense, the couple of studies I found on doing this in rats are nowhere near enough to convince me that this is a good idea.  This also falls under the logical fallacy of considering all probiotics to be the same.

5. A Healthy Bathroom Cabinet

Probiotic toothpaste, probiotic deodorant, probiotic nasal sprays.  If I had to bet, I’d guess that in 30 years all of these ideas will be put into practice in a widespread manner.  But without a lot more testing there’s no way I’m going to create a homemade probiotic nasal spray.

6. Probiotics for Pets

Not crazy.  If it works for us it should certainly work for pets.   However, we don’t know that it *does* work for us and we know even less about the microbiomes of our pets than we do our own.

7. Bacterial Bedfellows

This is a “probiotic mattress” that contains 5 species of bacteria that are supposed to “reduce humidity” and “magically clean up your bed textiles”.  Even ignoring another total misuse of the term “probiotic”, this sounds far-fetched to me.


David Coil

David Coil is a Project Scientist in the lab of Jonathan Eisen at UC Davis. David works at the intersection between research, education, and outreach in the areas of the microbiology of the built environment, microbial ecology, and bacterial genomics. Twitter

6 thoughts on “Probiotics: The Good, the Bad, The Unknown, and the Crazy

  1. Some nice thoughts here, I think you’re right that some claims re: probiotics are outrageous!

    Your mention of this company Optibac is possibly a bit harsh? When clicking through to the piece they’re clearly writing it as a lighthearted, exploratory piece – not asking people to use the facemasks etc – and padding out their statements with ‘this is reported to…’ ‘apparently has this effect’ etc! Whereas your piece sort of implies they’re pushing these uses?

  2. Gareth,

    Fair enough. It’s true that they’ve padded their statements… but on the other hand it’s a bit credulous to talk about so many unsubstantiated applications while elsewhere claiming to be scientific.

  3. I give probiotics to my dogs when they take antibiotics because doing so prevents diarrhea. I don’t know why but it works. Still I was troubled when my vet offered me a probiotic that was for both dogs and cats.

  4. No question there is a lot of snake oil in the supplement market as a whole. However i think you are wrong to include the Yokult product as an image in your rant. It is easy to find web articles that are crazy with claims on various supplements (heck trying reading up on the supposed benefits of kombucha). I once fielded a phone call from a woman who wanted me to validate her religiously inspired probiotic cocktail for horses that contained some 120 strains! There certainly are lots of unvalidated claims out there.

    However, the specific strain in Yakult (Lactobacillus casei Shirota) has a long history and a significant number of papers behind it (do a google scholar search). Might not be all the proof we all want to see given the (relatively) new world of gut microbiota research but aren’t peer reviewed studies where we’d like to see this go? Lumping Yakult in with your other comments doesn’t fit.

  5. David,

    That’s a fair point. In fact I didn’t mean to paint Yakult with the same brush. It was just an easily accessible image of a well-known probiotic.

  6. There are a wealth of clinical data that validates the benefits of probiotics. With mras resistance everywhere, probiotics is one of the approach to fight these antibiotic-resistant strains.

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