A Guide to Probiotics

PROBIOTICS… what a buzzword these days! I’ve seen probiotics marketed in everything from tea to shampoo. So let’s dig in and see what they are and if they are worth all they hype.

What are Probiotics?

Well to understand what probiotics are you first need to understand that our gut (specifically colon) is FULL of microorganisms both good and bad. Probiotics are good bacteria found in foods or supplements intended to have a positive effect on your gut health(1-3). This positive effect may be by achieved by increasing the number of these healthy bacteria, or increasing the diversity of the microorganisms. The effects of probiotics are strain specific(1-3) and cannot be generalized. Therefore, if you are using them to help target a particular health concern it is important to do your research on which strain, or combination of strains may best fit your needs.

So why do we need these good bacteria in our gut?

A healthy mix of bacteria in your colon (called your microbiome) can have positive effects throughout your body. They are directly involved in metabolism and immunity. These “good bacteria” are responsible for digesting fiber to produce short chain fatty acids (SCFA’s) which provide energy to the colonic cells and help regulate the pH balance of the colon(1-3). Simply put, they help your digestion run smoothly.  A number of factors impact how many and how diverse the bacterial profile of your gut are such as age, stress, infections, changes in diet, and antibiotic use(2). 

Possible Health implications

This topic is still relatively new, and requires tons more research to make definitive claims about anything. But there are a few prospective positive and negative health implications worth talking about.


Probiotics have been shown to have immune enhancing effects, however there is no definitive explanation for how this happens. They may function by producing antibacterial substances, helping to kill pathogens, or strengthening a physical barrier in the gut that prevents “bad bacteria” from sticking around(1-5). 

Heart health:

There is promising research showing that certain strains of probiotics have positive effects on heart health by lowering cholesterol. Basically, this is thought to happen by reducing liver’s ability to make cholesterol and by breaking down cholesterol into bile acids which can then be eliminated via feces(1). 

Gut Health (IBS, Diarrhea):

Probably the most common medical use of probiotics is to prevent or treat diarrhea. Different causes of diarrhea are affected by probiotics in various ways.  

Antibiotic use can lead to diarrhea because it kills off the good and the bad bacteria in your gut. This makes the body more susceptible to pathogens and alters the metabolism of some of the foods we eat(1) because the good bacteria in our gut help break down nutrients that were not broken down in the small intestine. There is convincing evidence that probiotics can be used to help prevent and treat diarrhea associated with the use of antibiotics(1,6),  in fact, they are prescribed with antibiotics in the hospital I work at to help prevent antibiotic associated diarrhea. I even presented a journal club proposition on this topic to my superiors during my dietetic internship!

Another common form of diarrhea is “traveller’s diarrhea” which happens commonly when individuals from industrialized countries travel to developing countries and are exposed to new bacteria such as E. coli, Campy, and Salmonella(1). There is some evidence that shows Lactobacilli, Bifidobacteria, Enterococci and Streptococci can be used prior to and during a vacation to help prevent traveler’s diarrhea(1). 

Irritable bowel syndrome (IBS), a chronic condition characterized by recurrent abdominal pain, bloating, gas, diarrhea and/or constipation. Certain combinations of probiotic strains have been shown to help relieve these symptoms. There is promising research on a common combination of probiotics known as VSL#3 in relieving gas and bloating for people suffering from IBS(1). 

Supplements VS. Food:


Probiotic supplements are complicated. They vary by strain types, amounts, and form. The most commonly seen strains fall into the categories of Lactobacillus or Bifidobacterium, but even within these two categories there are many different species which produce different effects. As with all supplements I recommend choosing a brand that has undergone third party testing and doing research into which product best fits your needs. If you are looking for a supplement to help alleviate symptoms of a medical condition, consult with a doctor or dietitian to determine which probiotic strains are best for your individual needs.

Food sources:

Probiotics are traditionally found in fermented foods such as sauerkraut, yogurt, kimchi, kombucha, miso, tempeh, and kefir(7). As the health benefits of probiotics continue to emerge they have also been added to foods that they would not naturally be found in.  Keep in mind these foods are not tightly regulated by the FDA or USDA so it is difficult to determine what and how many strains are present in any given product.


Probiotics are safe to be consumed in foods for the majority of people. If you are experiencing and gastrointestinal problems such as stomach pain, bloating, constipation, cramping, or diarrhea I recommend that you see a doctor to identify the cause of your symptoms before starting and probiotics.

If you are a healthy individual not displaying any of these symptoms, there is really no need to spend money on a probiotic supplement for daily use. Try incorporating the probiotic containing foods mentioned above into your diet a few days a week. As for supplementation, I would recommend using them prior to and during your travels as well as any time you take antibiotics.


  1. Pandey, K. R., Naik, S. R., & Vakil, B. V. (2015). Probiotics, prebiotics and synbiotics- a review. Journal of Food Science and Technology, 52(12), 7577–7587. https://doi.org/10.1007/s13197-015-1921-1
  2. Slavin, J. (2013). Fiber and Prebiotics: Mechanisms and Health Benefits. Nutrients, 5(4), 1417–1435. https://doi.org/10.3390/nu5041417
  3. Gourbeyre, P., Denery, S., & Bodinier, M. (2011). Probiotics, prebiotics, and synbiotics: impact on the gut immune system and allergic reactions. Journal of Leukocyte Biology, 89(5), 685–695. https://doi.org/10.1189/jlb.1109753
  4. Wu, D., Lewis, E. D., Pae, M., & Meydani, S. N. (2019). Nutritional Modulation of Immune Function: Analysis of Evidence, Mechanisms, and Clinical Relevance. Frontiers in Immunology, 9. https://doi.org/10.3389/fimmu.2018.03160
  5. Liu, H., Wang, J., He, T., Becker, S., Zhang, G., Li, D., & Ma, X. (2018). Butyrate: A Double-Edged Sword for Health? Advances in Nutrition, 9(1), 21–29. https://doi.org/10.1093/advances/nmx009
  6. Videlock, E. J., & Cremonini, F. (2012). Meta‐analysis: probiotics in antibiotic‐associated diarrhoea. Alimentary Pharmacology & Therapeutics, 35(12), 1355–1369. https://doi.org/10.1111/j.1365-2036.2012.05104.x
  7. Marco, M., Heeney, D., Binda, S., Cifelli, C., Cotter, P., Foligne, B, et al. (2017). Health benefits of fermented foods: microbiota and beyond. – PubMed – NCBI. Retrieved April 30, 2019, from https://www.ncbi.nlm.nih.gov/pubmed/27998788

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