Probiotic: A live microorganism that provides health benefits.

A complex ecosystem – including more than 400 bacterial species – lives in your gut. Small populations live in your stomach and small intestine, but the majority of these bacteria live in your colon. These bacteria provide many benefits to you, including helping digestion, synthesizing vitamins and nutrients, breaking down medications, supporting the development and function of the gut, and enhancing the immune system.

There is also research showing that probiotics help with problems in other parts of your body.

For example, some people say they have helped with:

  • Skin conditions
  • Urinary and vaginal health
  • Preventing allergies and colds
  • Oral health
  • Improved Mood

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What are probiotics?

Simply put, probiotics are bacteria and yeasts that are good for your health.

The health benefits of probiotics have been recognized for some time, and a large body of scientific research – including clinical trials – has confirmed the benefits of probiotics in supporting a healthy digestive tract and a healthy immune system. Notably, the FDA states that probiotics must contain at least one billion live cells per serving to be beneficial.


Types of Probiotics

There are number of bacterial families that you will find in probiotics. The two main bacterial species found in most probiotics are Bifidobacterium and Lactobacillus.

Lactobacilli are the most common probiotic bacteria and they are often found in yoghurt and fermented foods. Particular strains of Lactobacillus have been found to be long-term residents of the gastrointestinal tract.

Strains associated with a favorable gut environment include:

  • Lactobacillus paracasei
  • Lactobacillus plantarum
  • Lactobacillus rhamnosus
  • Lactobacillus salivarius
  • Lactobacillus acidophilus
  • Lactobacillus casei
  • Lactobacillus fermentum
  • Lactobacillus gasseri
  • Lactobacillus johnsonii


Bifidobacteria mainly occur in the gastrointestinal tract of mammals, birds, and insects, but are also found in sewage, human breast milk, fermented milk, cheeses, and water kefir.

Helpful probiotic strains of Bifidobacteria include:

  • Bifidobacterium adolescentis
  • Bifidobacterium animalis
  • Bifidobacterium bifidum
  • Bifidobacterium breve
  • Bifidobacterium longum


In general, B. bifidum and B. longum are the dominant species in infants, whereas B. adolescentis and B. longum dominate the adult gut microbiota. Analysis of healthy adult microbiomes has shown that they contain between 0 -4 different species of Bifidobacterium.  The most common species detected are:

  • B. longum (present in 90% of adults), 
  • B. adolescentis (present in 79% of adults),
  • B. catenulatum (present in 38% of adults).


The other types of probiotic that may arguably be the most effective are the butyrate-producing bacteria. There are very few probiotics that contain this type of bacteria. The biggest producers of butyrate are bacteria that contain either butyrate kinase or via butyryl CoA:acetate CoA transferase, both of which are enzymes that catalyze the production. This includes bacteria from the genera Clostridium, Eubacterium, Fusobacterium, Roseburia, and Faecalibacterium. The ones that you are most likely to find in a probiotic supplement are:

  • Clostridium butyricus
  • Streptococcus faecalis


How do probiotics work?

This basically falls into the category of how does the gut microbiome keep us healthy?

The short answer is that we don’t really know, but scientists are quickly starting to figure it out (See the Microbiome Bites blog for the most recent breakthroughs).

There are currently 3 major mechanisms that are proposed to explain the beneficial actions of probiotics:

  1. Enhancing repair of the gut lining by Lactobacilli-induced production of Reactive Oxygen Species (ROS). This is particularly relevant to the probiotic strain Lactobacillus rhamnosus GG.
  2. The production of short chain fatty acids (SCFAs) by lactic acid bacteria that are absorbed by the cells lining the gastrointestinal tract.
  3. Making antimicrobial substances that kill bad bacteria and then taking over their turf.

Are probiotics safe?

Yes probiotic foods and supplements are safe for the majority of people. Those with immune system problems or other serious health conditions shouldn't take them.  The FDA regulates probiotics the same way they regulate food.




Ishikawa, E., Matsuki, T., Kubota, H., Makino, H., Sakai, T., Oishi, K., et al. (2013). Ethnic diversity of gut microbiota: species characterization of Bacteroides fragilis group and genus Bifidobacterium in healthy Belgian adults, and comparison with data from Japanese subjects. J. Biosci. Bioeng. 116, 265–270. doi: 10.1016/j.jbiosc.2013.02.010. Article (paywall).

McCartney, A. L., Wenzhi, W., Tannock, G. W. (1996) Molecular Analysis of the Composition of the Bifidobacterial and Lactobacillus Microflora of Humans. Appl. Environ. Microbiol. Dec;62 no. 124608-4613. PDF.

Rivière, A., Selak, M., Lantin, D., Leroy, F., De Vuyst, L. (2016) Bifidobacteria and Butyrate-Producing Colon Bacteria: Importance and Strategies for Their Stimulation in the Human Gut. Frontiers in Microbiology. 7; 979. doi:10.3389/fmicb.2016.00979. Article (free).

Turroni, F., Peano, C., Pass, D. A., Foroni, E., Severgnini, M., Claesson, M. J., et al. (2012). Diversity of bifidobacteria within the infant gut microbiota. PLoS ONE 7:e36957. doi: 10.1371/journal.pone.0036957. Article (free).