The world is a big and complex place. Numerous different substances and life forms make up the system that we call Earth. Our planet is so vast that we have a hard time wrapping our heads around it and understanding how all of its constituents hang together. In order to make things easier for ourselves, we break it into smaller pieces, which we label and study in isolation. Some people, such as car mechanisms, focus all of their attention on the various compounds that make up motorized vehicles; others, such as marine biologist, are primarily interested in what goes on in the biotic environment of the sea; and yet others, such as nutritionists, are primarily concerned with the food substances that nourish our species.
All of these groups of experts have taken it upon themselves to organize and classify the many things that make up their field of study. Car producers and mechanics describe cars according to their speed, performance, and composition; marine biologists try to make sense of the complicated world that is found inside the oceans of our planet by labeling and organizing its constituents according to a biological system; and nutritionists and nutritional scientists put the foods we humans eat under a magnifying glass and study and categorize the many nutrients and compounds that make their way into human bellies around the world.
The upside of doing things this way is that we humans – as a species – become very knowledgeable about many different things. The downside is that specialization often leads to oversimplification. History has shown us that we humans often fail to see the big picture of things. We tend to stand too close to the trees, failing to see the forest.
This leads us over to the main topic of this article…
The recent birth of probiotics
Quite recently in our evolutionary history – in 1675 to be more exact – we humans discovered that there are invisible life forms present here on Earth. Prior to that time, we were largely unaware of the fact that there are living things surrounding us that we can’t see with our naked eyes. In the years that have passed since then, an entire field has been created and devoted to the invisible critters of the world. The field I’m talking about is microbiology.
This field has evolved greatly since it first came into existence. Not only have we discovered and explored more and more life forms over time, but our general understanding of the workings of the microbial world has also greatly improved. We’ve understood that not all microbes are out to do us harm, but that many actually do us a lot of good. Very recently, we even created a name for these friendly bugs: probiotics.
The microbes that we call probiotics are those that are believed to improve our health when we ingest them in “adequate” quantities. No probiotic became a probiotic over night. In order to earn their name, all probiotics had to go through fairly extensive scientific experiments. Only those microbes that have been shown in clinical trials to be useful for improving human health are put up for “the probiotic selection committee”.
To most people, this probably seems like a good way of doing things. However, others, such as myself, are not so fond of this system…
The shaky science of probiotics
The fact that a specific microbial strain has “done well” in a clinical study doesn’t necessarily mean that it’s wise and healthy for the average Joe to take a capsule every day that contains this strain. The main problem with clinical trials and other experimental studies on probiotics is that most of them lack a follow-up period. They don’t assess whether the microbe in question is actually able to colonize the human gut or if it brings about some permanent changes in the microbiotas of the study participants.
It’s well known that probiotics are able to stimulate the human immune system and suppress the survival of many pathogens; hence, it shouldn’t come as a surprise that many clinical studies on probiotics have shown that probiotic consumption brings about some acute health improvements in the study participants. What’s important to note though, is that these effects tend to disappear once the probiotic is discontinued; they are only transiently present. As some of the most experienced researchers in the microbiome field has pointed out, some probiotics, in particular lactic acid-producing probiotics, may, via their impact on the microbiota of the gut, actually cause more harm than good over the long term, in the sense that they can disturb the gut ecosystem, suppressing the growth and functions of some of its members (1). Obviously, for this to happen, fairly large quantities of probiotics would have to be consumed. A teaspoon of probiotic yoghurt with breakfast is unlikely to do much harm. However, regular consumption of large quantities of probiotic foods or supplements certainly can.
When we think about it, this isn’t really surprising. The human gut microbiota is a complex ecosystem composed of hundreds of different microbial species. Like any other ecosystem, it changes in accordance with its environment. It’s a very unnatural behavior for a human to take in large numbers of just one or a couple of microbial strains on a regular basis. Prior to the recent development of probiotic supplements and foods produced via starter cultures, it was impossible to do this.
This brings us over to the second problem with the probiotic concept…
It’s a mistake to think that some of the microbes that colonize our bodies are unequivocally good whereas others are unequivocally bad
All of the microbes that colonize our bodies are part of a larger system, in which they occupy different niches. Some microbes are indeed friendlier than others – We’ve all heard about the dangers of C. difficile and Salmonella bacteria, haven’t we? – however, none are purely good or purely bad. Whether a microbe is “good” or “bad” depends on the prevailing environmental conditions, as well as the perspective of the classifier.
Microbes evolve rapidly, adapting to their environment. Some “good” bacteria can “break bad” if certain mutations evolve and spread, whereas “bad” bacteria can sometimes do good things. Even in a healthy gut, potentially pathogenic bacteria are present. It’s not like a healthy person harbors a gut filled with “probiotics”. Actually, most of the microbial strains found in today’s probiotic products don’t even set up shop in the human intestine. They either disappear from the gut or diminish in presence as soon as the person in question no longer consumes the probiotic product.
The point I’m trying to get across here is not that all probiotics are bad, but rather that the approach of labelling bacteria as good and bad is overly simplistic. Lactic acid bacteria – the primary type of bacteria found in most probiotic foods and supplements – are only one of the many types of bacteria that are found in the human gut. A well-functioning gut ecosystem doesn’t just depend on these microbes for its stability and resilience; it depends on many others as well.
Diversity trumps uniformity
You want your gut to look like a natural, undisturbed ecosystem composed of many different life forms; you don’t want it to look like a monoculture crop. In many ways, the probiotic approach –which involves pouring one or a few types of organisms into the human gut – is analogous to the monoculture approach to farming. In both cases, uniformity trumps diversity.
This is problematic, because an ecosystem that lacks diversity tends to be less hardy than an ecosystem in which many different species are present. This is true regardless of whether the environment of the ecosystem in question is the human gut, an ocean, or any other habitat. This idea is supported by a solid body of evidence, including recent studies that have looked into the stability and functions of the human gut microbiota (2, 3, 4, 5).
Many different types of microorganisms are needed for a well-functioning gut, in part because different microbes specialize in degrading different foodstuffs. A gut microbiome that is diverse with regards to its genetic prowess is better able adapt to environmental change than a microbiome that’s rid of diversity.
All of this is to say that it’s probably much better to focus on gradually building a healthy, diverse gut microbiota, for example by occasionally eating small quantities of fermented vegetables (which, in contrast to probiotic supplements and many industrially produced probiotic foods, contain a microbial ecosystem, not just a handful of bacteria), consuming an ancestral, fiber-rich diet, and picking up bacteria from healthy plants, humans, and pets, than to stuff one’s gut full of “probiotics”.
Moving forward, I believe we should strive to develop supplements and other products that contain a broad range of microbes that are adapted to live in the human gut, as opposed to products that contain one or a couple of so-called probiotics. Efforts are already underway to do this. It will be interesting to see what the future holds!