How Much Do We Really Know About Probiotics?

Probiotics are made up of microorganisms that are the same as or similar to the microorganisms that occur naturally on and in our own bodies. These bacteria are important because they help our bodies function by digesting food, producing vitamins, and destroying disease-causing microorganisms (1). The two most commonly studied bacteria found in probiotics belong to the groups Lactobacillus and Bifidobacterium. They are commonly found in food sources such as yogurt or dietary supplements (1).

There is a large amount of information on probiotics that is unknown to us. In fact, the U.S. Food and Drug Administration (FDA) has not approved any probiotics for the use of preventing or treating any health problems (1). While we know probiotics are effective in treating some health problems, there is still a lot we do not know on this topic.

Probiotics can be helpful to treat some gastrointestinal issues by restoring the microbes found in our digestion tract and move things back to normal. For example, they can help treat some cases of diarrhea that are caused by a bacterial infection. However, they may not treat all types of diarrhea, such as those caused by viruses (2). Probiotics can also be useful to prevent or treat diarrhea that is associated with antibiotics. They may also be beneficial for treating constipation by aiding in the digestion process.

However, for other gastrointestinal issues such as a Helicobacter pylori infection (bacteria sometimes found in the digestive tract), liver disease, ulcerative colitis, or irritable bowel syndrome, there is not any strong evidence to suggest that probiotics are useful to prevent or treat these issues. It is important to remember that many of these specific bacteria in probiotics are not well studied and while one kind may help an illness, another kind may not have the same effect. There is no definitive research to say which exact types help and which do not, or what dosage of probiotics is most effective and in which population (1).

Another thing to keep in mind is you can’t always count on getting exactly what you want in probiotic supplements. A recent article in The New York Times discussed the use of probiotics as a dietary supplement (3). Upon inspection, more than 50% of these supplements had violations related to the strength and identity of the supplement. This just further highlights the fact that these supplements aren’t regulated so there’s no guarantee you are getting just probiotics in your bottle.

The good news is there are little to no side effects to trying these probiotics in the generally healthy population. However, there may be more severe effects in those who have other medical issues or weakened immune systems (1). If you’re unsure about taking a probiotic, it is always a good idea to ask your Doctor or a Registered Dietitian what they recommend before trying a product.

Amelia Quigley, Dietetic Intern


1. Probiotics: In Depth. National Center for Complementary and Integrative Health. NIH Website. Updated 2016. Accessed 2018.

  1. Wilkins T, Sequoia J. Probiotics for Gastrointestinal Conditions: A Summary of the Evidence. Am Fam Physician. 2017;96(3):170-177.
  2. Carroll, Aaron E. The Problem With Probiotics. The New York Times. Published October 22, 2018. Accessed December 2018.