I will avoid any semblance of suspense or drama here: I am a proponent of probiotics. I take one daily. I even helped formulate one, uniquely positioned for use at night.
My personal case is just an anecdote, but like all clinical anecdotes- it matters a lot to the person affected, in this case- me. As an adult, I developed a mild sensitivity to nuts; I would get some abdominal pain after eating them. As walnuts are a favored entry in my concept of a “complete breakfast,” and raw almonds on my short list of preferred snacks, this was quite annoying. I tried a good, multi-strain probiotic, and the problem went away. I enjoy walnuts, almonds, other nuts- and my daily (nightly) probiotic ever since.
There’s just a bit more to my personal story, too- namely, the reason why I might need a probiotic in the first place. I do all the things that should produce a fairly optimal microbiome- the ecosystem of diverse bacteria living on and in us- without recourse to ingested bacteria (that, in essence, is what probiotics are). I eat optimally, exercise daily, avoid toxic exposures to the best of my ability.
But I live in the modern world, and that’s enough to challenge and perhaps even preclude an entirely robust microbiome. I don’t need to take antibiotics to be exposed to them; trace amounts suffuse our food supply. The same is now true of pesticide residues, herbicide residues, and miscellaneous industrial toxins. Eating organic does not fully avoid these exposures, although it reduces them, because once contamination reaches a certain distribution, there is no escaping it until or unless we produce our food on a new and pristine planet. Don’t hold your breath.
So, however good our practices, we and our microbiome are challenged by the ways we have adulterated the once pristine environments on this planet, and inescapably so. A probiotic is a logical counter-measure.
With that as a prelude, what warrants the mention of “cons”? There are many potential entries here, including uncertainty about which are the best bacterial strains for whom; whether or not bacteria ingested for health benefit could ever produce direct harm in those with compromised immunity; and the risk of producing an imbalance in bacterial colonies with an attempt to do the converse. In other words, file the “law of unintended consequences” on the list of cons worthy, at least, of consideration.
But a recent provocation in the peer-reviewed literature gives us a far more specific concern to address. A study published in the prestigious journal Cell several months ago, and spawning media reaction and academic commentary ever since, reported on the effects of probiotics following a course of antibiotics.
The researchers gave antibiotics to both mice, and then humans, not to treat any disease- but to disrupt the microbiome. They then followed that disruption with probiotics delivering select strains, and evaluated the effects on the intestinal lining and the reconstitution of a balanced, healthy microbiome.
The punch line was that compared to a control group, probiotics interfered with the recovery of gut mucosa, and delayed the microbiome recovery- exactly opposite the intended effects. (Of note, fecal transplantation did accelerate recovery.)
I have generally recommended probiotics to patients and family as part of a post-antibiotic recovery plan, and yes, absolutely, I am reconsidering that now. Science evolves incrementally, and scientists are duty bound to keep pace. As an aside, one way to differentiate reliable and informed guidance from propaganda is to ask this question: does this source ever respond to new evidence with a change of mind/opinion/recommendation? The answer should certainly not be “every time,” because that suggests the source has no stable foundation of knowledge predicated on the weight of evidence in the first place. But if the answer is “never,” you are in the hands of a huckster, fool, or fanatic. Step away slowly, and whatever you do- resist any temptation to reach for your credit card.
Back to the probiotic study- how might we make sense of the finding, assuming that the general case for probiotics as microbiome support is valid? For those wanting the recondite, mechanistic considerations, I commend to you the study in Cell, where those are discussed by the authors. For our purposes here, I will make use of a simple analogy.
The goal of probiotics is to achieve a healthy, optimal balance among the bacterial colonies constituting the microbiome. The goal of a balancing pole in the hands of a tightrope walker is to achieve an optimal, healthy balance that prevents her/him from falling off that narrow perch.
A balancing pole will do no good in the hands of someone not qualified to walk that rope in the first place. Similarly, probiotics may have unexpected, unintended, and untoward effects depending on context. They no doubt interact with other exposures, from diet to drugs, genes to germs, just as the balancing pole interacts with the aptitudes, training, and constitution of the walker. All of this argues for a carefully personalized approach to probiotic use, a case the Cell authors make.
Even more flagrantly, a balancing pole placed across the body of a tightrope walker crumpled and bleeding on the ground after a fall would add something of an insult, and obviously no benefit at all, to such injury. The utility of the pole in achieving balance would not pertain to recovery after the injurious loss of balance. Perhaps the same is true of probiotics after antibiotics. Perhaps the intestines require the same initial period of convalescence as the fallen walker. The pole, and probiotics, are then once more useful only after that first, unperturbed recovery.
This is speculation on my part, but that is perhaps the principal conclusion here. We have many good arguments for probiotics, founded in science and sense. We have evidence that they can be used to fight dangerous infections, and perhaps even protect mental health. But we have doubts, gaps in our knowledge, and precautionary considerations, too. Informed speculation is the best we can do at present.
I remain, as noted at the start, a proponent- and will keep taking my probiotic routinely before bed (and enjoying walnuts and almonds). But I will stop recommending probiotics routinely right after antibiotics, and I will keep track of the evidence in this area as it accrues. I will change my mind, and my behavior, in tandem with the evolving evidence, as warranted.
The intent of probiotic use is to achieve and maintain a healthy balance in the microbiome. A balanced perspective on the relevant evidence as it comes in, with all due consideration of both pros and cons, is the only reliable way to get there from here.
David L. Katz, MD, MPH, FACPM, FACP, FACLM, is the Founding Director (1998) of Yale University’s Yale-Griffin Prevention Research Center, and current President of the American College of Lifestyle Medicine. He has published roughly 200 scientific articles and textbook chapters, and 15 books to date, including multiple editions of leading textbooks in both preventive medicine, and nutrition. He has made important contributions in the areas of lifestyle interventions for health promotion; nutrient profiling; behavior modification; holistic care; and evidence-based medicine. David earned his BA degree from Dartmouth College (1984); his MD from the Albert Einstein College of Medicine (1988); and his MPH from the Yale University School of Public Health (1993). He completed sequential residency training in Internal Medicine, and Preventive Medicine/Public Health. He is a two-time diplomate of the American Board of Internal Medicine, and a board-certified specialist in Preventive Medicine/Public Health. He has received two Honorary Doctorates.