Choosing a Probiotic

Dr. Erin Crossman, ND

Live active cultures:

There are many things that potentially contain probiotics. Probiotics are live microorganisms, that provide a health benefit to the host when given in adequate amounts. A common product people consider a dose of probiotics is in eating yogurt. But not all yogurts contain viable and clinically proven beneficial microorganisms. Things to look for in your yogurt include:

  • The ingredients list “live active cultures”.
  • The product has gone through quality control methods, ensuring adequate numbers of viable bacteria present throughout its shelf life. This is sometimes available on their websites or by contacting a product representative.
  • The list of ingredients include the specific genus, species, strains and their amounts.

Some types of microorganisms used in foods, often as food fermentation agents, have not directly been tested for health benefits. Certain health professionals may not consider these probiotics because they are not controlled for in terms of dose or type of microorganisms. There are many fermented foods containing potentially beneficial microorganisms but these are indicated more for maintenance of a healthy microflora. When seeking a targeted treatment plan and desired mechanism of action, other more controlled forms of probiotics may be necessary.

Human strains

Choose human strains, which means a probiotic that contains organisms originating from the human intestinal tract. Studies have shown there is a large amount of genetic variability within different strains of each type of bacteria e.g. L. acidophilus. Each strain is shown to be specific to its natural host. The strain originating from the human microbiome has developed to live and function in our specific environments better than other environments. This goes the opposite way when you are given non-human probiotic strains. They are strains that are specific to the functioning of another host and will not function to the best of their ability in humans.


As each specific genus, species, and their strains have unique properties of action, it’s important they are used accordingly. There are increasing amounts of scientific studies on strain properties and their influence on health, and our understanding continues to evolve.

For example, strains differ in their ability to adhere to the intestinal walls. Studies show that certain transient microorganisms, like the yeast Saccharoyces boulardii, do not permanently colonize colonic mucosa. Saccharoyces boulardii may be used for a shorter duration in order to outcompete less beneficial microorganisms and allow for the repopulation of beneficial species. In contrast, if the desired action is repopulating the microbiome, strains that adhere well and take up a more permanent residence are indicated.


The dose is dependant on the type of microorganisms, the targeted goal and the individual. With this, there aren’t always specific guidelines for dosing and recommendations can vary. One approach is in using smaller doses of probiotics for maintenance of a healthy microflora (potentially through fermented foods) and larger doses for targeted treatment plans.

A common question is if the listed dose is what is contained in the product before or after opening it. Generally if the product was stored adequately, the listed amount of colony forming units (CFU) will be present at the expiration date to guarantee potency. But as probiotics are living organisms, their potency will be affected by changes in their environment such as excess light, heat, moisture, and also considering if they are shelf stable or needing refrigeration.


Some types of probiotic products also contain prebiotics, such as fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), or inulin. Prebiotics act like the food for the probiotics. They are ingredients that are non-digestible by humans but are fermented by intestinal microorganisms and allow changes in the microflora composition and/or activity. Some people may have gastrointestinal upset, most commonly gas and bloating, from ingesting prebiotics in a product or in high prebiotic containing foods. This varies with each individual as well as the prebiotic type and dose. In contrast, prebiotics do not create undesirable symptoms in everyone.  Prebiotics can be beneficial because they are supplying elements necessary for the probiotics to thrive.

Be informed to make sure the types of probiotics you are taking are suited to your health goals. This can include talking to a healthcare professional who is educated on probiotics.


  1. Can, M., Besirbellioglu, B.A., et al. (2006) Prophylactic Saccharoyces boulardii in the prevention of anti-biotic-associated diarrhea: A prospective study. Med Sci Monit, 12(4): 19-22.
  2. Gibson, G.R., Probert, H.M., et al. (Dec. 2007) Dietary modulation of the human colonic microbiota: updating the concept of prebiotics. The Nutrition Society. 17(2): 259-275.
  3. Percival, M. (1997) Choosing a Probiotic Supplement. Clinical Nutrition Insights, Advanced Nutrition Publications, Inc., 6(1): 1-4. Retrieved from:
  4. Roberfroid, M. (Mar. 2007) Prebiotics: The Concept Revisited. The Journal of Nutrition. 137(3): 830s-837s.
  5. Sanders, M.E. (Spring 2009) How Do We Know When Something Called “Probiotic” Is Really a Probiotic? A Guide for Consumers and Health Care Professionals. Functional Food Reviews. 1(1): 3-12.
  6. Slavin, J. (Apr. 2013) Fiber and Prebiotics: Mechanisms and health Benefits. Nutrients. 5(4): 1417-1435. doi:  10.3390/nu5041417
  7. Tuomola, E., Crittenden, R., et al. (Feb. 2001) Quality assurance criteria for probiotic bacteria. American Journal of Clinical Nutrition. 73(2): 393s-398s. Retrieved from: