The Shaky Science of Probiotics
Th e fact that a specifi c microbial strain has performed well in a clinical study
doesn’t necessarily mean that it’s wise for everyone to take a daily capsule including
this strain. Th e main problem with clinical trials and other experimental studies
on probiotics is that most of them lack a follow-up period. Th ey don’t assess
whether the microbe in question is actually able to colonize the human gut, or if it
actually initiates any permanent shifts in the participants’ gut microbiota.
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 be surprising
that probiotic consumption has been shown in clinical trials to eff ect certain acute
health improvements in the participants. What’s important to note, though, is
that these eff ects are transient, persisting only as long as the probiotic regimen
is continued. Some seasoned researchers in the fi eld have noted that certain
probiotics—lactobacillus in particular—can actually cause more harm than good
over the long term, perturbing the GI ecosystem and suppressing the growth
and functions of some of its other members. 1 Obviously, fairly large quantities of
probiotics would have to be consumed for this to happen. A teaspoon of yogurt
with breakfast is unlikely to do much harm. However, regular consumption of
large quantities of probiotic foods or supplements certainly can.
When we think logically about it, this eff ect isn’t really surprising. Th e human gut
microbiome is a complex ecosystem, comprised of hundreds of diff erent microbial
species. As in any other ecosystem, one internal change can aff ect the entire web.
It’s highly unnatural for a human to consume 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.
Cue my second point...
It’s a mistake to assume that some microbes
residing in the human gut are unequivocally
good and that others are unequivocally bad.
All of the microbes in the human gut are part of a larger
system, in which they occupy diff erent niches. Some microbes are
indeed friendlier to humans than others; we’ve all heard about
the dangers of C. diffi cile and Salmonella bacteria. However,
none are purely helpful or purely harmful. Whether a microbe
is “good” or “bad” depends on the prevailing environmental
conditions, as well as the perspective of the classifi er.
Microbial species evolve rapidly, adapting to their
environment. Some “good” bacteria can “go rogue” if they
mutate and this new form proliferates; “bad” bacteria can,
sometimes, provide physiological benefi ts. Even in a healthy
gut, potentially pathogenic bacteria are always present.
Additionally, most of the microbial strains found in today’s
probiotic products aren’t even able to establish a foothold in
the human intestine. 2, 3 Th ey either disappear from the gut,
or diminish in presence as soon as the person in question no
longer consumes the probiotic product.
My point here is not that probiotics are useless, but rather
that labeling bacteria as “good” or “bad” is overly simplistic
and reductionist. Lactic-acid bacteria—the primary class 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 lactobacilli for its stability and resilience; it
depends on many others, as well.
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Diversity Beats Uniformity
Optimally, the human gut is a
robust, relatively untouched ecosystem
comprised of many diff erent life-forms;
it shouldn’t look like a monoculture
crop. In many ways, probiotic
supplementation—ingesting one or
a few types of organisms meant to
infi ltrate the human gut—is analogous
to the monoculture approach to
farming. In both cases, uniformity
trumps diversity.
Th is is problematic, because in
ecological terms, diversity confers
resilience. Th is is true regardless of the
context, whether it be the human gut,
an ocean, or any other habitat. Th is idea
is supported by a solid body of evidence,
including recent studies that have
examined the stability and functions of
the human gut microbiota. 4-7
A diverse array of microorganisms
are needed for a well-functioning
gut, in part because diff erent strains
specialize in degrading diff erent
foodstuff s. And again, greater diversity
also confers better adaptability to
environmental change (including
dietary change).
Hence, it’s probably much better to
gradually foster healthy, diverse gut
microbiota than to stuff the gut full of
“probiotics”. We can accomplish the
former via occasional consumption
of 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 strains), consuming an
ancestral, fi ber-rich diet, and picking
up bacteria from healthy plants,
humans, and pets.
Moving forward, 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 so-called
probiotics. Such eff orts are already
underway. It will be interesting to see
what the future holds.
January 2018 Paleo Magazine Express
11