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What are Probiotics?

Etymology: pro- + biotic

The word ‘probiotic’ might be best defined by an etymological hybrid, derived from the Latin preposition pro (“for” or “in support”) and the Greek adjective biotic from the noun bios (“life”)1

Probiotic meaning: ‘for life’ or ‘in support of life’

What are Probiotics?

What are the benefits of probiotics?

The beneficial effects of probiotics are associated with the modulation of the intestinal microbiota of the host and the capacity to interact with the immune system, both directly and mediated by microbiota of the host6.

Some of the most important and well-documented benefits of probiotics include7,8:

  • Prevention and treatment of GI tract issues (e.g., irritable bowel syndrome, gastrointestinal disorders, elimination of Helicobacter, inflammatory bowel disease, diarrheas)
  • Positive effect on allergic diseases (e.g., atopic dermatitis)
  • Improved digestion and heart health
  • Changes in bile salt conjugation
  • Reduced inflammation
  • Antibacterial activity (control and destroy harmful bacteria)
  • Anti-oxidative activity
  • Important for nutrient synthesis and to improve nutrient bioavailability and absorption
  • Aid in the synthesis of key neurotransmitters
  • Key role in vitamin B12, butyrate and vitamin K2 production 
  • Effective in the treatment of diseases such as obesity, insulin resistance syndrome, type 2 diabetes, and non-alcoholic fatty liver disease
  • Modulation of immune function (namely stimulating secretion of IgA and regulatory T cells)
  • Beneficial in certain cancers and associated side effects 
  • Reported to alleviate symptoms of AIDS, respiratory and urinary tract infections 
  • Beneficial effects on aging, fatigue, autism and osteoporosis

It is important to be aware that probiotic effects will always be case dependent, and their efficacy is dependent on strain, dose, and components of the probiotic in question7.

What are the mechanisms of action of probiotics?

Some of the mechanisms associated with the beneficial effects of probiotics7,8:

  • Antagonistic effect to harmful microbes (production of inhibitory and antimicrobial substances)
  • Blocking adhesion sites for pathogenic/ harmful bacteria
  • Competition with the pathogenic bacteria for nutrients
  • Modulation of immune responses of the host
  • Inhibition of bacterial toxin production (degradation of toxins and blocking of toxin receptors)

What is considered a good probiotic?

Several authors have identified some of the prerequisites of an ideal probiotic organism3,9,10:

  • Non-pathogenic (GRAS)
  • Lactic acid producer
  • Acid and bile tolerant
  • Effective adhesion to gut lining
  • Short generation time
  • Robust and surviving processing conditions
  • Anti-genotoxic property
  • Genetically stable

The FAO/WHO working group has also highlighted that efficacy of probiotics should be proven by human trials and those studies should show “significant improvement in condition, symptoms, signs, well-being or quality of life; reduced risk of disease or longer time to next occurrence; or faster recovery from illness.” And each claim correlated with the probiotic tested4.

Probiotic Strains

Probiotics may contain a variety of strains, but human probiotic microorganisms belong mostly to bacteria from the genus Lactobacillus and Bifidobacterium, which are the most studied and commonly used in functional foods and dietary supplements. Gram-positive bacteria belonging to the genus Bacillus and some yeast strains belonging to the genus Saccharomyces, are also used in certain probiotic products9. A next generation of probiotics, such as Faecalibacterium prausnitzii, Akkermansia muciniphila, or Clostridia strains have shown very promising results11.

Why is strain identity important?

Strong evidence supports the hypothesis that the efficacy of probiotics is both strain-specific and disease-specific12. For example, a 2018 study demonstrated strain-specific efficacy for preventing adult antibiotic-associated diarrhea using certain Lactobacillus species (e.g., by the mixture of Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus rhamnosus) while other Lactobacillus strains did not show efficacy12. (MacFarland 2018) Therefore, strain identity (genus and species) is important to link a strain to a specific health effect and to enable accurate surveillance and epidemiological studies4.

Probiotic foods 

What are Probiotics?

Probiotics are found in fermented foods, as well as in some supplements. Historically people would have plenty of probiotics from fresh foods, grown in healthy soils, and from using fermentation as a method of preserving food, which promotes the growth of beneficial bacteria. 

In current modern societies, refrigeration, excessive sanitation, and agricultural practices have greatly reduced the presence of beneficial bacteria in foods and human diets. Many foods even contain antibiotics and pesticides that kill the beneficial bacteria in our body.

What whole foods are rich in probiotics? 

Mostly raw fruits and vegetables (if organic and not disinfected) and fermented foods.

Best Whole Food Sources of Probiotics

  • Sauerkraut – Fermented Cabbage
  • Tempeh – Fermented Soybeans
  • Miso – Soybean paste
  • Natto – Soybeans fermented with Bacillus subtilis var. natto
  • Kombucha – Fermented tea (black or green)
  • Raw nut cheese
  • Coconut Kefir (alternative to the traditional cow or goat kefir)
  • Probiotic coconut yogurt
  • Kimchi – Spicy fermented cabbage
  • Pickles – Fermented or fresh pickled vegetables


Buy your foods organic, unprocessed or minimally processed, low in added salt, sugar, preservatives and extra ingredients, and do not overly wash or disinfect them.


  1. Hamilton-Miller JM, Gibson GR, Bruck W. Some insights into the derivation and early uses of the word ‘probiotic’. Br J Nutr. 2003 Oct;90(4):845. doi: 10.1079/bjn2003954. PMID: 14552330.
  2. Metchnikoff E (1907). Lactic acid as inhibiting intestinal putrefaction. In: The prolongation of life: Optimistic studies. W. Heinemann, London: 161-183.
  3. Fuller R. Probiotics in man and animals. J Appl Bacteriol. 1989 May;66(5):365-78. PMID: 2666378.
  4. Food and Agriculture Organization (FAO) Guidelines for the Evaluation of Probiotics in Food. FAO; London, ON, Canada: Report of a Joint FAO/WHO Working Group on Drafting Guidelines for the Evaluation of Probiotics in Food. 30 April–1 May 2002. htttp://
  5. Hill C, Guarner F, Reid G, Gibson GR, Merenstein DJ, Pot B, Morelli L, Canani RB, Flint HJ, Salminen S, Calder PC, Sanders ME. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol. 2014 Aug;11(8):506-14. doi: 10.1038/nrgastro.2014.66. Epub 2014 Jun 10. PMID: 24912386.
  6. de Vrese M., Schrezenmeir J. (2008) Probiotics, Prebiotics, and Synbiotics. In: Stahl U., Donalies U.E., Nevoigt E. (eds) Food Biotechnology. Advances in Biochemical Engineering/Biotechnology, vol 111. Springer, Berlin, Heidelberg.
  7. Markowiak P, Śliżewska K. Effects of Probiotics, Prebiotics, and Synbiotics on Human Health. Nutrients. 2017 Sep 15;9(9):1021. doi: 10.3390/nu9091021. PMID: 28914794; PMCID: PMC5622781.
  8. Harish K., Varghese T. (2006). Probiotics in human—evidence based review. Calicut Medical Journal. 4.
  9. Pandey KR, Naik SR, Vakil BV. Probiotics, prebiotics and synbiotics- a review. J Food Sci Technol. 2015 Dec;52(12):7577-87. doi: 10.1007/s13197-015-1921-1. Epub 2015 Jul 22. PMID: 26604335; PMCID: PMC4648921.
  10. Fuller R (1991). Probiotics in human medicine. Gut. 32(4), 439–42.
  11. Vallianou N, Stratigou T, Christodoulatos GS, Tsigalou C, Dalamaga M. Probiotics, Prebiotics, Synbiotics, Postbiotics, and Obesity: Current Evidence, Controversies, and Perspectives. Curr Obes Rep. 2020 Sep;9(3):179-192. doi: 10.1007/s13679-020-00379-w. PMID: 32472285.
  12. McFarland LV, Evans CT, Goldstein EJC. Strain-Specificity and Disease-Specificity of Probiotic Efficacy: A Systematic Review and Meta-Analysis. Front Med (Lausanne). 2018 May 7;5:124. doi: 10.3389/fmed.2018.00124. PMID: 29868585; PMCID: PMC5949321.