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Debunking Probiotics: Understanding How They Work, Common Myths, and How to Choose the Right One

Are you confused or overwhelmed with all of the information surrounding probiotics? If so, I don't blame you.

The other day, I was doom-scrolling on Instagram and I came across a post from a health influencer saying "If you take this one probiotic it will recolonize your gut microbiome and fix your gut issues”. I rolled my eyes and realized that this type of information is exactly why people are so confused.

I rolled my eyes for three reasons:

  1. It’s very rare that one supplement is going to be the answer for your gut health concerns, whether it's bloating, irritable bowel syndrome, constipation, diarrhea, or something else. When I prescribe probiotics it is almost always in combination with other treatment modalities.

  2. In order for a probiotic to work, you need to know what strain to use. A one-size-fits-all approach does not work... More on that below.

  3. And lastly, probiotics do not recolonize your gut microbiome, that’s a myth. I will tell you more about this, and what they actually do in a little bit.

Probiotics have captured widespread attention in the health and wellness space. These beneficial microorganisms can now be found in not only supplements and medicinal food products but also in the latest beauty and skincare formulations, household cleaning products, mouthwashes - even products for our pets.

With influencers, health journalists, and medical providers both touting and criticizing the benefits of these products, it can be difficult for a consumer to make sense of all the conflicting information.

What are probiotics?

The International Scientific Association for Probiotics and Prebiotics defines probiotics as "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host"(1).

Essentially, microscopic "bugs", typically bacteria, though sometimes fungi, when used at a therapeutic dose, offer a health benefit to the person taking them. For example, Saccharomyces boulardii, a non-pathogenic yeast, reduces the risk of antibiotic-associated diarrhea when taken concurrently with antibiotics (2). You may be more familiar with its brand name, Florastor, which can be found in the over-the-counter medication aisles of most pharmacies.

The history of probiotics

Probiotics have a rich history that stretches back to ancient times, well before the discovery of microbes. Egyptian hieroglyphs provide evidence of the use of fermented milk products, while Tibetan Nomads relied on fermented Yak milk to preserve their dairy during long journeys (3).

More recently, in the early 1900s, Russian scientist Elie Metchnikoff identified two strains of bacteria in the Bulgarian fermented beverage, now known as yogurt, which he believed were responsible for preventing what was then called, "protein putrefaction" and, consequently, diseases and even aging, that were thought to be linked to putrefaction (4).

Despite Elie's findings, research continued to largely focus on pathogenic, or disease-causing, microbes until about the 1990s to early 2000s. At this time, there was a stronger interest and more research in our own microbiomes - the collection of bacteria, fungi, and viruses that are naturally found inside and on us. Classically, we think about our gut microbiome, but we have others - our skin, vaginas, mouths, etc. These findings led to more advanced research into specific strains of probiotics and their benefits.

What are probiotics useful for?

Traditionally, probiotics have been associated with the management of gastrointestinal diseases such as irritable bowel syndrome, inflammatory bowel disease, and antibiotic-associated diarrhea.

However, emerging research suggests their potential benefits extend beyond the realm of gastrointestinal health, encompassing concerns like anxiety, depression, asthma, insulin resistance, and many others (5, 6, 7, 8).

How do probiotics work?

Contrary to popular belief, probiotics generally don't permanently colonize, or take up residence, in the gut.

Instead, they function through various mechanisms depending on the specific strain. Some of the most common mechanisms of action of probiotics include:

  • Keeping out unwanted bugs: In vitro studies have shown that probiotics may resist letting potentially harmful (opportunistic) bugs colonize in the gut, protecting us from potential diseases. (9, 10).

  • Increase the production of helpful substances called metabolites. One of the most important are short-chain fatty acids which are important energy sources for the cells that line our digestive tract. (11,12).

  • Support our gut lining: Probiotics upregulate proteins used to form our intestinal barrier. (13)

  • Modulating our immune system and inflammation: Probiotics can adjust how our immune system works, helping it respond appropriately to different situations, whether it needs to rev up or calm down. (14, 15).

  • Increase gut motility: probiotics may increase our motility, aka the contractions our digestive tract uses to move things along. (16, 17, 18).

  • Vitamin production: In other in vitro studies, probiotics have been shown to synthesize certain vitamins including types of B vitamins and vitamin K (19, 20).

How are bacteria/probiotics categorized?

I mentioned above the mechanism of action depends on the strain of the probiotic, what does that mean?

Probiotics are categorized into genus, species, and strains.

  • Genus is a broad category, grouping organisms with similar properties.

  • Species is a further narrowed category within the genus.

  • Strain refers to the specific subtype or genetic variation of that species.


A commonly used example to illustrate this is the classification of dogs. All dogs are part of the genus Canus, but there are several species in the Canus family including wolves (lupus), dogs (familiaris), coyotes (latrans), and jackals (aureus). Further, within the species of dogs, there is significant variation in breeds - think about a St. Bernard, Pomeranian, and Golden Retriever - all very different. Dog breeds are the equivalent of strains. Though St. Bernards and Pomeranians are part of the same genus and species, they are very different. This is the same for probiotics, though two strains of probiotics may have the same genus and species, they can have very different effects on the body (21).

Which probiotic should you take?

When it comes to probiotics, there isn't solid research backing their use for "general health".

Instead, the approach we favor is to harness the power of probiotics for specific conditions.

Think of it like finding the perfect key for a lock. Because strains can vary in action so significantly even in the same species, the key lies in selecting specific strains that have been studied and shown beneficial to address particular health concerns.

Examples of specific strains for certain conditions include:

  • Intra-vaginal Lactobacillus acidophilus A-212, Lactobacillus rhamnosus A-119, Streptococcus thermophilus A-336 given prophylactically led to reduced reoccurrence rates of bacterial vaginosis (BV) and Gardnerella vaginalis in women with a history or recurrent BV compared to placebo (22).

  • In those with irritable bowel syndrome, constipation dominant, Saccharomyces cerevisiae CNCM I-3856 reduced abdominal pain/discomfort and significantly improved stool consistency after 8 weeks of treatment (23).

  • In children, there was a reduced risk of development of atopic dermatitis, or eczema, in those who supplemented with Lactobacillus rhamnosus HN001 in infancy (24).

While generally safe, probiotics may exacerbate certain medical conditions. Consulting a healthcare provider well-versed in probiotic use is advised to avoid unwanted outcomes and unnecessary expenses. Always discuss any changes to your healthcare regimen with your provider first.

Questions? Let us know below! We're happy to address them on our socials for everyone to benefit.


  1. Hill, C., Guarner, F., Reid, G., et al. "Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic." Nature Reviews. Gastroenterology & Hepatology, vol. 11, no. 8, 2014, pp. 506-514. DOI:10.1038/nrgastro.2014.66.

  2. Szajewska, H., Mrukowicz, J. "Meta-analysis: non-pathogenic yeast Saccharomyces boulardii in the prevention of antibiotic-associated diarrhoea." Alimentary Pharmacology & Therapeutics, vol. 22, no. 5, 2005, pp. 365-372. DOI:10.1111/j.1365-2036.2005.02624.x.

  3. Guo, X., Long, R., Kreuzer, M., et al. "Importance of functional ingredients in yak milk-derived food on health of Tibetan nomads living under high-altitude stress: a review." Critical Reviews in Food Science and Nutrition, vol. 54, no. 3, 2014, pp. 292-302. DOI:10.1080/10408398.2011.584134.

  4. Metchnikoff, E. (1908). Optimistic Studies. New York: Putnam's Sons, pp. 161-183.

  5. Kim, S. K., Guevarra, R. B., Kim, Y. T., et al. "Role of Probiotics in Human Gut Microbiome-Associated Diseases." Journal of Microbiology and Biotechnology, vol. 29, no. 9, 2019, pp. 1335-1340. DOI:10.4014/jmb.1906.06064.

  6. Slykerman, R. F., Hood, F., Wickens, K., et al. "Effect of Lactobacillus rhamnosus HN001 in Pregnancy on Postpartum Symptoms of Depression and Anxiety: A Randomised Double-blind Placebo-controlled Trial." EBioMedicine, vol. 24, 2017, pp. 159-165. DOI:10.1016/j.ebiom.2017.09.013.

  7. van de Pol, M. A., Lutter, R., Smids, B. S., et al. "Synbiotics reduce allergen-induced T-helper 2 response and improve peak expiratory flow in allergic asthmatics." Allergy, vol. 66, no. 1, 2011, pp. 39-47. DOI:10.1111/j.1398-9995.2010.02454.x.

  8. Hulston, C. J., Churnside, A. A., Venables, M. C. "Probiotic supplementation prevents high-fat, overfeeding-induced insulin resistance in human subjects." British Journal of Nutrition, vol. 113, no. 4, 2015, pp. 596-602. DOI:10.1017/S0007114514004097.

  9. Collado, M C et al. “Role of commercial probiotic strains against human pathogen adhesion to intestinal mucus.” Letters in applied microbiology vol. 45,4 (2007): 454-60. doi:10.1111/j.1472-765X.2007.02212.x

  10. Muñoz-Quezada, Sergio, et al. “Competitive Inhibition of Three Novel Bacteria Isolated from Faeces of Breast Milk-Fed Infants against Selected Enteropathogens.” British Journal of Nutrition, vol. 109, no. S2, 2013, pp. S63–S69., doi:10.1017/S0007114512005600.

  11. Schneider, Stephane-M et al. “Effects of Saccharomyces boulardii on fecal short-chain fatty acids and microflora in patients on long-term total enteral nutrition.” World journal of gastroenterology vol. 11,39 (2005): 6165-9. doi:10.3748/wjg.v11.i39.6165

  12. Wullt, Marlene et al. “Lactobacillus plantarum 299v enhances the concentrations of fecal short-chain fatty acids in patients with recurrent clostridium difficile-associated diarrhea.” Digestive diseases and sciences vol. 52,9 (2007): 2082-6. doi:10.1007/s10620-006-9123-3

  13. Rose, Elizabeth C et al. “Probiotics, Prebiotics and Epithelial Tight Junctions: A Promising Approach to Modulate Intestinal Barrier Function.” International journal of molecular sciences vol. 22,13 6729. 23 Jun. 2021, doi:10.3390/ijms22136729

  14. D'Amelio, P, and F Sassi. “Gut Microbiota, Immune System, and Bone.” Calcified tissue international vol. 102,4 (2018): 415-425. doi:10.1007/s00223-017-0331-y

  15. Karczewski, Jurgen et al. “Regulation of human epithelial tight junction proteins by Lactobacillus plantarum in vivo and protective effects on the epithelial barrier.” American journal of physiology. Gastrointestinal and liver physiology vol. 298,6 (2010): G851-9. doi:10.1152/ajpgi.00327.2009

  16. Wang, Bingxian, et al. "Luminal administration ex vivo of a live Lactobacillus species moderates mouse jejunal motility within minutes." The FASEB Journal 24.10 (2010): 4078-4088.

  17. Kunze, Wolfgang A., et al. "Lactobacillus reuteri enhances excitability of colonic AH neurons by inhibiting calcium‐dependent potassium channel opening." Journal of cellular and molecular medicine 13.8b (2009): 2261-2270.

  18. Bär, F., et al. "Cell‐free supernatants of Escherichia coli Nissle 1917 modulate human colonic motility: evidence from an in vitro organ bath study." Neurogastroenterology & Motility 21.5 (2009): 559-e17.

  19. LeBlanc, Jean Guy et al. “Bacteria as vitamin suppliers to their host: a gut microbiota perspective.” Current opinion in biotechnology vol. 24,2 (2013): 160-8. doi:10.1016/j.copbio.2012.08.005

  20. Liu, Yue et al. “Long-chain vitamin K2 production in Lactococcus lactis is influenced by temperature, carbon source, aeration and mode of energy metabolism.” Microbial cell factories vol. 18,1 129. 6 Aug. 2019, doi:10.1186/s12934-019-1179-9

  21. Schoch, C. L., et al. "NCBI Taxonomy: a comprehensive update on curation, resources and tools." Database (Oxford), 2020, baaa062. DOI:10.1093/database/baaa062.

  22. Ya, W., Reifer, C., Miller, L. E. "Efficacy of vaginal probiotic capsules for recurrent bacterial vaginosis: a double-blind, randomized, placebo-controlled study." American Journal of Obstetrics and Gynecology, vol. 203, no. 2, 2010, pp. 120.e1-120.e1206. DOI:10.1016/j.ajog.2010.05.023.

  23. Cayzeele-Decherf, A., Pélerin, F., Leuillet, S., et al. "Saccharomyces cerevisiae CNCM I-3856 in irritable bowel syndrome: An individual subject meta-analysis." World Journal of Gastroenterology, vol. 23, no. 2, 2017, pp. 336-344. DOI:10.3748/wjg.v23.i2.336.

  24. Wickens, K., et al. "A protective effect of Lactobacillus rhamnosus HN001 against eczema in the first 2 years of life persists to age 4 years." Clinical and Experimental Allergy: Journal of the British Society for Allergy and Clinical Immunology, vol. 42, no. 7, 2012, pp. 1071-1079. DOI:10.1111/j.1365-2222.2012.03975.x.


The information in this blog is not intended or implied to be a substitute for professional medical advice, diagnosis or treatment. All content, including text, graphics, images and information, contained on or available through this blog is for general information purposes only. Modrn med and Dr. Mary Pardee make no representation and assume no responsibility for the accuracy of information contained in or made available through this blog, and such information is subject to change without notice. This blog does not provide medical services, diagnosis or counsel. You are encouraged to confirm any information obtained from or through this email with other sources, and review all information regarding any medical condition or treatment with your physician. Never disregard professional medical advice or delay seeking medical treatment because of something you have read on or accessed through this information.

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4 comentários

So if we don't think we have a condition, do we need to take probiotics? And what is the relation of probiotics to digestive enzymes? What questions or tests should we ask for from our Dr if we think we need some?


Nicole Salemme
Nicole Salemme
14 de dez. de 2023

What strain of probiotics should someone with depression and anxiety take? What about someone who is in recovery from bulimia?

MJ Yoga
MJ Yoga
18 de dez. de 2023
Respondendo a

The healthaid probio mood was good if you'd like to try it


My newborn had to get antibiotic. Could this impact his microbiome? Is there a probiotic I could take that could transfer through my breastmilk to him?

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