top of page

6 Things to Know About Probiotics

Updated: Jun 4, 2020

Defining Probiotics

When you break down the word, pro and biota mean “for life” [1]. Probiotics consist of live microorganisms (including yeasts and bacteria) that when taken in adequate amounts, impart a health benefit to the host [2][3][4]. This is different to a prebiotic which is a non-digestible food component that nurtures the growth or activity of beneficial microorganisms in your gut [2][5]. Some prebiotic foods include Jerusalem artichoke, garlic, onions, apples and wheat bran to name a few [6].

Sources of Probiotics

So where do probiotics come from? Mostly from fermented foods and healthy humans [3]. One of the best food sources of probiotics is yoghurt. Other sources with less well characterized or proven probiotics include certain cheeses, kimchi, kombucha, sauerkraut, miso, pickles and raw unfiltered apple cider vinegar [7]. These other food sources contain microorganisms but may not necessarily qualify as probiotics.

Several probiotic supplements on the market are isolated from healthy humans for better compatibility with our digestive systems [3]. One of the exceptions is Saccharomyces boulardii, a yeast first isolated from tropical fruit, which has shown clinical effectiveness for diarrhea [8]. New sources of probiotics continue to be explored from fruit, grains and dairy products [3].

6 Things You Should Know About Probiotics

  1. The strain matters. Research conducted on one strain shouldn’t be extrapolated to others [9]. What does this mean? Go for strains that have clinical evidence behind them. For example, Lactobacillus rhamnosus strain GG has been shown to be effective for antibiotic-associated diarrhea [7].

  2. You can take them when you are on antibiotics and in fact, doing so can decrease side effects [10] [11]. Make sure to consume your probiotics a few hours apart from your antibiotics though.

  3. Take them with or just before a meal containing healthy fats as this can aid bacterial survival [12]. Some bacterial strains may also survive better when taken with carbohydrates [13].

  4. You can consume probiotics in food form such as Bio-K or supplements as both have demonstrated therapeutic benefits. If you are looking to consume specific strains, a probiotic in supplement form may be better.

  5. The dose matters. Dose is expressed in colony forming units (CFU), which represents the number of live microorganisms [7]. The amount can range based on the bacterial strain and purpose of use with typical doses of 5 to 10 billion CFUs/day for children and 10 to 20 billion CFUs/day for adults. Higher doses are not unsafe but may be more expensive and unnecessary, unless a certain condition requires greater concentrations. To obtain the right dose, quality also matters so choose reputable brands [14].

  6. For continued benefit, you will likely need to consistently take the probiotic as they only colonize the gut temporarily [2].

Mechanism of Action

To have an appreciation for probiotics and how they work, let’s discuss the microorganisms living in our gut.The human gastrointestinal tract contains trillions [15] of microorganisms which include bacteria, archaea, viruses, fungi and protozoa. These can all play a role in human health and disease [7].

A large proportion of probiotics consist of bacteria and a smaller number of fungi. Bacteria alone in our intestine weigh up to 1kg. That’s equivalent to about a 1 Liter bottle of water. The human gut is host to over 500 bacterial species [2]! What do these do for us? A lot! They aid in digestion, providing nutrients and play a role in the development of the immune system. Approximately 10% of our daily energy requirements come from the products of bacterial fermentation [2].

Despite all their benefits, we often associate bacteria with disease. So the thought of adding fuel to the fire by ingesting more bacteria seems rather odd. However, probiotics can positively impact human health by both treating and preventing illness [16].

Typically, probiotics transiently colonize the gastrointestinal tract even if they are of human origin [6]. Think of them as visitors or tourists that interact with and impact their environment, eventually leaving. For the time they are present, probiotics exert many beneficial effects some of which include [7]:

  1. Inhibiting the growth of pathogens

  2. Producing beneficial compounds, including short-chain fatty acids for use as energy sources [17]

  3. Altering the acid/base balance by decreasing the pH in the colon for a healthier environment

  4. Strengthening the intestinal barrier which has implications in leaky gut

  5. Vitamin synthesis, including K and B vitamins [18]

  6. Positive effects on the endocrine, immune and nervous systems

  7. Modifying gut transit time to normalize bowel movements [19]

  8. Anti-inflammatory [20]

  9. Toxin neutralization

  10. Breaking down bile – the fluid involved in fat digestion

  11. Increasing enzyme activity, which aids in digestion

Health Benefits

These are numerous and research is still ongoing. Probiotics have shown promise for various conditions ranging from gastrointestinal disorders, to allergies, skin concerns and infections [21].

How Are Probiotic Strains Selected?

When selecting and characterizing a probiotic, the WHO and FAO require the following [3]:

  1. Stress tolerance. It must survive digestive conditions including enzymes that help break down food, the body’s internal temperature, acidity, gastric juices and bile salts. A large number of isolated microorganisms are excluded based on their inability to tolerate the conditions of the digestive tract.

  2. Ability to adhere to the intestinal mucosa. A probiotic should be able to adhere to epithelial cells lining the gastrointestinal tract so they can exert beneficial effects for the time they are present.

  3. Inhibition of pathogens. Upon adherence to the gut, probiotics should be able to produce antimicrobial compounds and outcompete pathogenic bacteria.

  4. Safety assessment. Established criteria include records of isolation, proper identification and absence of harmfulness, infectivity, toxicity and transferable antibiotic resistance genes.

  5. Clinical trials. To evaluate safety and effectiveness.

Adverse Effects

No supplement is immune to adverse effects! Each person is unique as are their reactions to what they apply topically or take internally. Although probiotics can be beneficial and are generally safe, choosing the right clinically proven strain is key.

Some potential side effects to keep in mind [22]:

  1. Digestive symptoms including increased gas and bloating

  2. May cause infections in those with suppressed immune systems

  3. Allergies or intolerances. Read the labels for probiotics containing dairy, eggs or soy

  4. Headaches

As the world of probiotics can often be a challenging one to navigate, I would speak to a healthcare professional who can help you choose the most appropriate ones for your concerns and current state of health.


  1. Health Benefits of Taking Probiotics. Harvard Health Publishing. Accessed from:

  2. Ciorba, M.A. 2012. A Gastroenterologists’s Guide to Probiotics. Clinical Gastroenterology and Hepatology. 10(9): 960-968.

  3. De Melo Pereira, G.V., et al. 2018. How to Select a Probiotic? A Review and Update of Methods and Criteria. Biotechnology Advances. 36: 2060-2076.

  4. Hill, C., et al. 2014. 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 and Hepatology. 11:506-514.

  5. Probiotics: What You Need to Know. National Center for Complementary and Integrative Health. Accessed from:

  6. Sameco, A. 2016. The 19 Best Prebiotic Foods You Should Eat. Healthline. Accessed from:

  7. Probiotics. National Institutes of Health. Accessed from:

  8. More, M.I. and Swidsinski, A. 2015. Saccharomyces boulardii CNCL I-745 supports regeneration of the intestinal microbiota after diarrheic dysbiosis – a review. 8: 237-255.

  9. Marteau, P. 2011. Evidence of probiotic strain specificity makes extrapolation of results impossible from another, even from the same species. Annals of Gastroenterology and Hepatology.

  10. Rodgers, B. et al. 2013. PURLs: prescribing an antibiotic? Pair it with probiotics. Journal of Family Practice. 62(3): 148-150.

  11. Guo, Q. et al. 2019. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database Systematic Review. 4: CD004827.

  12. Tompkins, T. A. et al. 2011. The impact of meals on a probiotic during transit through a model of the human upper gastrointestinal tract. Beneficial Microbes. 2(4): 295-303.

  13. Corcoran, B.M. 2005. Survival of Probiotic Lactobacilli in Acidic Environments is Enhanced in the Presence of Metabolized Sugars. Applied and Environmental Microbiology. 71(6): 3060-3067.

  14. Kligler, B. et al. 2008. Probiotics. American Family Physician. 78(9):1073-1078.

  15. Valdes, A.M. et al. 2018. Role of the gut microbiota in nutrition and health. BMJ. 361: k2179.

  16. Liu, Y. et al. 2018. Probiotics in Disease Prevention and Treatment. Journal of Clinical Pharmacology. 58(Suppl 10): S164-S179.

  17. LeBlanc, J.G. et al. 2017. Beneficial effects on host energy metabolism of short-chain fatty acids and vitamins produced by commensal and probiotic bacteria. Microbial Cell Factories. 16:79.

  18. Hill, M.J. 1997. Intestinal flora and endogenous vitamin synthesis. European Journal of Cancer Prevention. 6 Suppl 1: S43-45.

  19. Choi, H.C. 2015. Alteration of Gut Microbiota and Efficacy of Probiotics in Functional Constipation. Journal of Neurogastroenterology and Motility. 21(1): 4-7.

  20. Prado, M.R.M. 2019. Chapter 9 – Anti-inflammatory effects of probiotics. Discovery and Development of Anti-Inflammatory Agents from Natural Products. Pages 259-282.

  21. Probiotics: What You Need to Know. National Center for Complementary and Integrative Health. Accessed from:L

  22. 5 Possible Side Effects of Probiotics. Healthline. Accessed from:


bottom of page