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Do probiotics really work? (Part-I)


“Should I take a probiotic?”


Some people say probiotic supplements are the answer to whatever ails you: digestive complaints, brain fog, immune system problems—even cancer.


And then there are those who liken probiotics to multivitamins: a surefire method of creating very expensive urine—or in this case, poop.


The truth is, taking a probiotic can be worth it.


But any potential benefits depend on factors like: Who’s taking the probiotic? Under what circumstances? And for what goal?


What are probiotics?


According to the World Health Organization (WHO), probiotics are “live microorganisms, which when administered in adequate amounts, confer a health benefit on the host.”


A simpler definition would be:


Probiotics are bacteria (and sometimes yeasts) that offer health benefits.


Probiotics come in supplement form and are also found in various fermented dairy products.


Based on the current evidence, fermented dairy, such as yogurt and kefir, is the only food that can be considered probiotic.


Other fermented foods like kimchi, sauerkraut, kombucha, natto, and miso may have health benefits, but aren’t probiotic because they don’t contain the types of bacteria that fit the definition above. Also, pickled foods don’t fit the definition either, though they’re certainly delicious.


There are dozens of strains of probiotics.


They often have long names that may seem difficult to remember and even harder to spell. 


The full name of each strain includes its genus, species, subspecies (if applicable), and an alphanumeric designation that serves as an identifier.


Unless you’re a scientist, you’ll mostly hear strains referred to by just their genus and species (i.e. Lactobacillus reuteri or Bifidobacterium longum).


Occasionally, you’ll also see the specific strain included by name and/or numeric identifier.


These distinctions can be important because, in some cases, different strains of the same genus and species have very different effects. For example, Escherichia Coli Nissle is probiotic, but Escherichia Coli Shiga (sometimes shortened to just E. Coli) is pathogenic, meaning it’ll make you sick.


To put this into real-life terms, at the genus level, we’re talking about the difference between a dog and a wolf. When we get down to the strain level, it’s like specifying between a dog and a dingo.


Some of the most common probiotic strains come from following genera (not to confuse you more, but genera is the plural of genus):


  • Lactobacillus
  • Bifidobacterium
  • Saccharomyces (these ones are actually yeast!)
  • Streptococcus
  • Enterococcus
  • Escherichia
  • Bacillus


Lastly, some probiotic supplements contain multiple strains. Often, these are given a special product name, such as VSL#3, a multi-strain probiotic with Lactobacillus, Bifidobacteria, and one strain of Streptococcus that you’ll learn more about later in this article.


Why are probiotics a thing?


A lot of times, people hear “bacteria” and think, ‘Oh, that’s the stuff that makes you sick.’ But our bodies are actually packed with different types of bacteria and other microbes—especially our gut.


That’s what we mean when we talk about the gut microbiome, the complex ecosystem of microbes (and their genetic material) that live in our GI tract.


These microorganisms are with us when we’re born, and they do more than just freeload. When everything’s working properly, they:


  • help ferment undigested nutrients to produce beneficial compounds, in some cases (those are called postbiotics)
  • prevent harmful bacteria and yeast from overpowering the gut by starving them out or actually attacking them (cool, right?!)
  • play a part in regulating immune responses to infections and potential allergens
  • influence energy balance and potentially body composition
  • may (potentially) influence mood, behavior, and cognition.


As you can see, our GI microbes have several important and wide-ranging jobs. So it’s understandable that people want to prioritize their gut health. Thus, the interest in probiotics.


But what are we actually talking about when we use the term “gut health”?


It depends on the context. But usually, when we talk about having a healthy gut, we mean:


Having a diverse gut microbiome with a wide array of different types of microbes and microbial genes.


Diversity is crucial, because it prevents one niche group of microbes from overpowering the rest of the population, which could make you sick.


It’s also important because we know our gut microbes have key metabolic and immune functions related to their genetic material. Except… we don’t totally know which microbes do what.


So a wider variety of microbes means more genes to perform a variety of functions to support our health.


When there isn’t a wide enough array in a person’s gut, it’s called dysbiosis. You might hear people saying gut dysbiosis is bad and scary, and that you need probiotics to “fix” it. You may also hear that dysbiosis causes leaky gut, also known as intestinal permeability.


It’s true that dysbiosis can cause problems or signal there’s a problem in your gut, and that probiotics might help. But not always. That’s because…


There’s no single “healthy” gut profile.


A healthy person’s gut profile (or the different types and amounts of microorganisms they have in their gut) could look completely different from another healthy person’s gut.


The same goes for people with various diseases: two people with the same GI disease, for example, may have vastly different gut profiles.


So while probiotics can help in certain situations , there’s still a lot we don’t know about how our gut works and what probiotics can do. And when it comes to gut health overall, we often say we’re being sold a problem so we can buy a solution.


That’s why it’s important to keep your eyes and ears open for disinformation and sales tactics related to gut health.


In particular, watch out for anyone/anything claiming that:


  • gut dysbiosis, gut imbalance, or leaky gut is the cause of any disease
  • they can diagnose, treat, cure, or prevent dysbiosis or leaky gut
  • you need supplementation, detoxing, or any sort of “gut reset”
  • they can design a specific diet for you based on the microbes in your gut
  • there’s a specific profile of a “healthy” gut or dysbiosis
  • they have the ability to directly modify your gut microbiota in a specific way
  • studies from rodent or cell culture are directly representative of the human gut microbiome


The bottom line: There’s still so much we don’t know about the gut microbiome that it’s impossible to define “good” or “bad” gut health.


The benefits of probiotics aren’t a sure thing.


At most, we have moderate evidence that certain probiotic strains might help alleviate certain health issues.


Turns out, it’s very tricky to do research and draw conclusions on the benefits of probiotics. That’s because:


There are hundreds of known strains of gut bacteria.


And potentially hundreds or thousands more that we haven’t been able to identify yet. It’s going to take a while to sift through them all and understand their effects.


Designing high-quality research is tough.


There’s no standardization in:

  • Probiotic strains
  • Dosage for trials
  • Treatment time


So when we look at the outcomes of different studies, they may not be comparable due to how the research was designed. That can make it difficult to draw conclusions.


Much of this research is done on animals.


These studies are useful in telling us how things might work in the gut, but we can’t extrapolate the findings to humans.


There may be some bias in which strains get studied.


Certain strains tend to come up more often in research than others. When scientists see that a certain strain seemed effective in one study, they might (consciously or unconsciously) select it for another study.


Also, some research may be funded by commercial entities (for example, a specific brand of yogurt), which affects which strains are studied.


Ultimately, this all means we have less information about some strains, and more information about others.


Response to probiotics is highly individual.


A supplement might work wonders for one person—but offer no benefit to another—due to differences in gut profiles and other factors.


What’s more, some people appear to be resistant to supplementation.


One study had a group of people take a Lactobacilli supplement. Then, researchers sedated each volunteer and then inserted a long, flexible tube into their intestines to see if the probiotic strains had successfully enriched their gut.


(If this sounds hauntingly like your last colonoscopy, you’d be right on.)


Researchers also asked volunteers to hand over their feces for analysis.


The results? The scientists found remnants of the probiotic in everyone’s poop. But during the colonoscopies, they discovered some participants’ guts weren’t enriched with the probiotic strains. For these people, the probiotics essentially passed right through them. So…


Finding #1 was that people responded differently to the probiotic strains.


Finding #2 Fecal counts were not a reliable measure of how well a probiotic “worked” in this study. And most studies use fecal counts as their main measure of how well a probiotic “worked.”


Measuring whether probiotics “work” is tricky.


Just because you pooped out microbes doesn’t mean they took up residence and started multiplying in your gut, as evidenced by the study mentioned above. But taking samples from a person’s gut requires, well, getting a tube stuck into your intestines. And it’s not always easy to find enough people who are willing to endure that in the name of science.


Reference: Precision Nutrition