What Do Probiotic Bacteria Actually Do in the Body?

What Do Probiotic Bacteria Actually Do in the Body?

  • Gut Health

  • Probiotics 101

  • By Desiree Nielsen, Registered Dietitian

    We keep hearing that probiotics are good for us — a controversial claim, as there is a lot of misinformation circulating both for and against taking a probiotic supplement. So how do we know what is true … and what probiotics actually do in the body? 

    At Bio-K+, we are passionate about making the best probiotics for gut health … but also about science. In fact, everything that goes into the product is based on decades of research. So, let’s talk about what probiotic bacteria are, what they are not, and what they actually do for you.

    Probiotics are specific strains of bacteria that have been shown to have health benefits — so not all bacteria are probiotics simply because they ferment food. Yes, that’s right: although fermented foods play a supportive role in a microbiome-friendly diet, it is not true to say that fermented foods such as yogurt or sauerkraut are probiotics. The reasons for this are: A) we often don’t know exactly what microbes are in a given food, and B) fermented foods often don’t contain enough microbes to have a therapeutic effect.

    Does this surprise you? Here are some other myth-busting facts about the beneficial bacteria we call probiotics.

    Fact: Probiotic bacteria do not permanently colonize your microbiome.

    As far as the microbiome is concerned, the first two or three years of life are marked by constant fluctuations, but once that phase is over, the resident strains in your gut microbiome are actually quite stable. The microbiome is said to have plasticity, which means that if something changes temporarily, such as eating differently on vacation or taking antibiotics, your microbiome tends to bounce back. 

    And those strains play an important role in determining which bacteria are welcome to hang out—or colonize—and which are not. So, it’s concerning that some probiotics are marketed with “colonizing” strains. In reality, no probiotic is meant to colonize and become a permanent resident of your gut microbiome. When probiotic manufacturers mistakenly refer to “colonizing” strains, they are actually referring to human strain bacteria. Bio-K+ probiotics are 100% human strain bacteria.

    Fact: It’s impossible — and unnecessary —to mimic the diversity of your microbiome with a probiotic.

    We’ve been hearing about the microbiome for so long that most of us understand that a healthy human gut microbiome is one that is diverse; so diverse, in fact, that the average person has about 1,000 species of bacteria living in their gut! 

    For this reason, it makes intuitive sense that a multi-strain probiotic will be better than a single-strain one. It’s more diverse, right? Except that’s not how it pans out in real life. For starters, it is impossible to mimic the diversity of your unique microbiome with a supplement. Sprinkling 20 strains of bacteria is only a drop in the bucket of the microbiome.

    Luckily, a highly diverse probiotic is not necessary. Research shows that the right probiotic can actually foster a healthier environment in which your own bacteria can thrive. For example, research suggests that taking Lactobacilli bacteria can actually increase the number of other species, such as Bifidobacterium, living in the gut!

    Fact: More bacteria are not always more effective.

    Another issue to consider is how much probiotic to take. Again, the “more is more” principle seems to apply, but in fact, each strain — or combination of strains — has its own effective dose. While it’s true that research suggests that doses of more than 10 billion CFUs are better, there are evidence-based probiotics that achieve lower (and even significantly higher!) effective doses.

    So, what do probiotic bacteria actually do in the gut?

    If probiotics do not take over your microbiome, what do they actually do? When you take a clinically proven probiotic, the bacteria perform many functions:


    • they take over the metabolic functions of a healthy gut microbiome, such as producing useful enzymes like lactase, or producing short-chain fatty acids;
    • they interact with your immune and nervous systems to your benefit; for example, some probiotics can help reduce the risk of colds and flu;
    • they help fight more harmful bacteria such as Escherichia coli and Clostridioides difficile;
    • they help maintain a proper pH so that your entire microbiome benefits.


    What about Bio-K+ specifically? It has been clinically proven that the bacteria in Bio-K+ do more than just inhibit the growth of Clostridioides difficile bacteria. More importantly, the Bio-K+ strains appear to reduce the amount of toxin produced by C. difficile and neutralize its effects.

    This is especially important when you are taking broad-spectrum antibiotics, which wipe out scores of beneficial bacteria in the gut, allowing harmful strains, such as those that cause antibiotic-associated diarrhea (loose stool), to take over. Think of probiotics as community support for a healthier gut. 

    How do you know if your probiotic is a good one?

    When it comes to choosing a good probiotic, look to the science. Many store-bought probiotics have no clinical evidence to support their use. Need a checklist? The Clinical Guide to Probiotic Products Available in Canada is an excellent resource to see at a glance if your probiotic is supported by scientific evidence. This is one of the ways that Bio-K+ stands out. Bio-K+ has over 20 years of research behind it, so we know how it works—and what it does in the body, including reducing symptoms of irritable bowel syndrome and helping to prevent antibiotic-associated diarrhea.




    • Wastyk, Hannah C et al. “Gut-microbiota-targeted diets modulate human immune status.” Cell vol. 184,16 (2021): 4137-4153.e14. doi:10.1016/j.cell.2021.06.019
    • Wieërs, Grégoire et al. “How Probiotics Affect the Microbiota.” Frontiers in cellular and infection microbiology vol. 9 454. 15 Jan. 2020, doi:10.3389/fcimb.2019.00454
    • Han, Shengyi et al. “Probiotic Gastrointestinal Transit and Colonization After Oral Administration: A Long Journey.” Frontiers in cellular and infection microbiology vol. 11 609722. 10 Mar. 2021, doi:10.3389/fcimb.2021.609722
    • Yang, Jing et al. “Species-Level Analysis of Human Gut Microbiota With Metataxonomics.” Frontiers in microbiology vol. 11 2029. 26 Aug. 2020, doi:10.3389/fmicb.2020.02029
    • Ray, Kathryn J et al. “Gut Bifidobacteria enrichment following oral Lactobacillus-supplementation is associated with clinical improvements in children with cystic fibrosis.” BMC pulmonary medicine vol. 22,1 287. 28 Jul. 2022, doi:10.1186/s12890-022-02078-9

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    Desiree Nielsen Registered Dietitian
    About the author
    Desiree Nielsen is a registered dietitian, author and host of the vvegetarian ccooking sshow, The Urban Vegetarian. Desiree takes an evidence-based, integrative approach to her dietetics work, with a focus on anti-inflammatory, plant-centredcentered nutrition and digestive health.
    View all articles by Desiree Nielsen
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