One of the biggest diet mistakes I’ve ever made was to take in large quantities of probiotics (in the form of fermented foods and supplements) on a daily basis. This behaviour harmed my microbiome and undermined my health.
Unlike what a lot of people seem to believe, probiotics – microorganisms that are believed to provide health benefits when consumed – are not harmless. Actually, in certain situations, they may cause a lot of damage. The term probiotics, which means pro life, is somewhat misleading, in the sense that probiotics don’t always promote life, sometimes they cause death. Some probiotics, including various types of lactic acid bacteria, produce powerful compounds (e.g., bacteriocins) that inhibit or kill other microbes. If you ingest large quantities of these critters on a regular basis, you may damage your gut microbiota and experience a range of adverse health effects.
Microbes are ruthless
We humans live in a bubble. Over the past 10.000-15.000 years, we’ve gradually separated ourselves from nature. We’ve lost touch with the natural world and it’s easy to forget that we, like all other organisms on this planet, are a part of complex, global ecosystem. All of the members of this system are fighting to survive; they compete among each other and adapt to their environment in order to avoid extinction.
Sometimes, the survival of one organism jeopardizes the survival of another. Some plant and animal species compete for the same resources and seek to exploit the same niches in their habitat. The ones that are best equipped to achieve this objective flourish, while those who don’t possess the traits that are required to win the competition wither or die out.
The same types of wars are fought within the invisible, microbial kingdom here on earth. Microbes are no different from larger organisms in that they too do whatever they can to survive. In many ways, the battle for existence that takes place in the microbial world is even more ruthless than the one that occurs among macroscopic life forms.
Microbes have been on this planet for a much longer time than we have. Over billions of years, they’ve evolved an ability to produce a long list of toxins, acids, and other compounds, some of which aid their survival by blocking the growth and survival of other, competing organisms.
You probably know that nasty bugs such as C. difficile and certain types of E. coli bacteria produce toxins that harm many other organisms. You may also be aware of the fact that it’s not we humans who designed antibiotics such as penicillin, but rather microbes. Penicillin was derived from fungi; it wasn’t created by humans in a lab.
What you may not know, though, is that it’s not just the stereotypical pathogens that produce toxins that damage other life forms – some microorganisms that are generally thought of as friendly do as well. For example, some types of probiotic lactobacilli have been shown to produce bacteriocins that inhibit or kill certain other types of bacteria (1). Not necessarily just closely related species, but also sometimes unrelated critters.
Unlike the toxins that are produced by pathogens such as C. difficile; the compounds that probiotics produce don’t have a direct, harmful effect upon the human body. If they had, the microbes couldn’t have been classified as probiotics. However, these probiotic-produced substances may inhibit the growth of certain commensal bacteria in the gut, thereby compromising the stability, diversity, and resilience of the gut microbiota.
This doesn’t mean that you should completely avoid probiotics – some are useful. What I’m trying to say is that we shouldn’t view probiotics as unequivocally good. Whether they enhance or undermine our health depends on several factors, in particular the current state of our gut microbiota and the quantity of probiotics consumed.
The consumption of large quantities of probiotics is an evolutionarily novel behavior that can disturb and destabilize the gut ecosystem
One of the first things I typically do when I set out to investigate a health-related topic is to look at the evolutionary evidence pertaining to the subject at hand. Evolution doesn’t necessarily provide us with clear-cut answers as to what we should eat and how we should live to achieve good health, but it does equip us with a guiding model that helps us to make sense of why the world is like it is and what types of behaviors and practices that different organisms are adapted for. It also helps us understand what types of foods we should include in our diet – and perhaps even importantly, which ones we should avoid.
It wasn’t until after the Agricultural Revolution that we humans started producing and consuming large quantities of fermented foods such as wine and yoghurt. Our Paleolithic forebears may have eaten smaller quantities of fruits and berries that had started to ferment, but they didn’t possess the tools or knowledge that are needed to make large batches of fermented foods via controlled fermentation. This notion is supported by anthropological research, including studies showing that contemporary hunter-gatherers primarily consume fresh food (2, 3, 4). It’s certainly possible that some of our late Paleolithic ancestors knew how to control the fermentation process and consumed fermented foods on a regular or semi-regular basis, but as a whole, I think it’s safe to say that fermented foods were not an important part of Paleolithic human diets.
Probiotic supplements and food products that are made using industrial starter cultures are obviously even more recent additions to the human diet. It’s only over the past few decades that these types of nutritional products have become widely available to the public. By itself, this doesn’t necessarily mean that we should completely avoid probiotic supplements and probiotic-enriched drinks; however, it does suggest that we should think twice before we choose to incorporate these products into our diet.
Modern scientific research has shown that virtually every time we deviate from the dietary path that was carved out for our species by evolutionary forces over millions of years, bad things happen. Our microbiota configuration changes, our genome expresses itself in an abnormal way, and we become inflamed (3, 4, 5, 6).
A large influx of probiotics represents an evolutionarily novel stimulus for the human gut microbiota. No studies have specifically looked at how high-potency probiotics affect the stability and diversity of the human microbiota. That said, there is little doubt in my mind that a daily intake of large quantities of probiotics can disturb and destabilize the microbial ecosystem that is found deep in the human gut. This notion is based on everything I’ve read about microbial systems and ecology, as well as my own personal experience.
If new organisms are put into an ecosystem, the dynamics of that ecosystem are going to change. This is true regardless of whether the ecosystem in question is found in the human gut, a rainforest, a lake, or any other milieu. For example, if you put a lot of large predators into a rainforest, the ecosystem in that area will likely change. The creatures that are inserted into the system may seek to exploit niches that are already occupied by other organisms and they may attack, kill, and perhaps cause an extinction of other animal species.
Microbial systems are obviously different from those that are made up of larger organisms; however, they too adhere to the laws of evolution. When new microbes are inserted into an ecosystem, things are bound to happen. The immigrants may produce certain compounds that are not normally present in large quantities in the environment, and could, on their way through the system, “push” other bacteria aside (1). Some of the immigrants may be able to set up shop in the milieu in which they’ve now entered; however, others may simply pass through. Unfortunately, many probiotics simply pass through the human gut, they aren’t capable of colonizing the intestine.
Taking a good probiotic supplement (there aren’t many of them out there) on a semi-regular basis or adding some fermented vegetables to your dinner plate every now and then is unlikely to do you much harm. Most likely, it will do you good. A daily intake of large quantities of probiotics, on the other hand, can – and most likely will – do you a lot of harm. This is particularly true if you consume mostly industrially produced probiotic products.
The amount of probiotics that you can handle without experiencing adverse health effects largely depends on the state of your gut microbiota. If you harbor a diverse, stable microbiota, you are more resilient than if you harbor a degraded, dysbiotic biome.
I know I’ve said it before, but I think it’s worth repeating: The goal is not to flood the gut with probiotics, but rather to push the microbiota in a “healthy” direction and bring in new, beneficial bugs that are capable of growing in the gut. I’m very skeptical of the recommendation made by probiotic manufacturers to take a probiotic pill every day, indefinitely.