Let’s talk about a really hot topic in gastroenterology: Probiotics. I get more questions about this topic than a lot of others, and it is challenging because the published evidence provides differing opinions. How do I feel about them? Personally, I’m, well…pro…probiotics. Get it?

Anyway, let’s start with the most basic question: what are probiotics? As per the World Health Organization (WHO), ‘they are live organisms, which when administered in adequate amounts confer a health benefit on the host.’ That sounds great but there are often hundreds of products claiming to be probiotics in the grocery store. How do I know which ones work? Well, to be considered a probiotic, it must contain enough bacteria that can survive passing through the gastric acid of the stomach and bile of the small intestine. There are three main organisms that can make up probiotics: Lactobacilli, Bifidobacteria, yeast (most commonly saccharomyces). A great source for available probiotics containing these organisms can be found at: This is a great reference (non-commercial website) to choose a certain product.

Usually, our bodies do a great job of keeping various bacteria in balance, but our bacteria shift as we have shifts in our health, diet, and environment. Next, let’s focus on the benefits of probiotics. The International consensus statement in 2014 accepted that probiotics do offer a general health benefit. It is theorized that probiotics do two main things: improve the overall gut health and modulate immune function. More specific effects of different strains of probiotics can block pathogenic bacteria (stop the bad guys), promote epithelial homeostasis (keep your gut intact), and induce neuromodulatory effect (hijack your gastrointestinal nerves…in a good way). In essence, different strains of bacteria offer different benefits that include those listed below in the figure.

Figure 1: Probiotic Health Benefits

2017 and 2018 brought the medical community large studies addressing probiotics and their effect on two specific disease entities: Functional Bowel Disease and Clostridium Difficile. Functional bowel disease is one of the most common gastrointestinal disorders and can manifest as unexplained diarrhea, nausea, abdominal pain, chest pain, heartburn, excess belching, excess flatulence, constipation, fecal incontinence and more. Two large studies published showed improvement in abdominal pain and discomfort in patients using probiotics compared to placebo. While none of these studies can not recommend definitively that probiotic use leads to improvements in functional bowel disease, they can say there was modest benefit in symptoms during intake of probiotics.

Clostridium difficile infection (CDI) causes a severe diarrheal infection when the bad bacteria (specifically Clostridium difficile) outnumbers the good bacteria. This occurs often times after taking antibiotics which kill the good bacteria and eventually lead to the shift. Two large trials looking at Clostridium difficile infection (CDI) and probiotic showed administration of probiotics closer to the first dose of antibiotics reduces the risk of CDI by more than 50% in hospitalized adults and each day of delay in initiating probiotics caused an 18% increase in the log odds of CDI. What does this mean for us? It means that while we can’t say for sure that probiotics will prevent CDI or cure IBS, it means that there is a positive relationship. Healthcare providers will continue to spend time and energy developing trials studying the positive relationship to establish causation.

Are they safe?

For the most part, probiotics are considered safe if you have a functioning immune system as confirmed by a systematic literature of probiotic safety published in 2014. The biggest side effect seen in patients that use probiotics is gas and distention. However, critically ill patients requiring hospitalization in the Intensive Care Unit, patients with short gut syndrome, or immunocompromised patients should not take probiotics. Immunocompromised patients are those with weakened immune system include patients with AIDS, cancer or transplant patients taking immunosuppressive medications, and those with inherited diseases that affect the immune system. These populations are at an increased risk of developing an invasive infection from the probiotics. It’s just not worth the risks for such a minimal benefit.


Lastly, keep in mind that probiotics are considered dietary supplements. This means insurance companies will not cover the costs. In addition, the Federal Drug Association (FDA) will not regulate them. As a result each each formulation contains different organisms, and different concentrations of organisms making them very difficult to study and compare. Given the limitations, physicians are unable to suggest optimal doses or duration of treatment. 

Take home message:

  • Discuss your concerns and symptoms with your physician. Inform them if you are on probiotics.
  • The aforementioned website is a great source for all commercially available probiotics along with trials.
  • Different probiotic strains possess unique properties for benefitting host physiology.
  • One probiotic dose does not fit all illnesses, selection should be based on clinical indication and published trials.
  • Symptomatic benefits are modest, if at all. Probiotics are best used to supplement other therapies.
  • Continuous consumption of probiotics throughout a period of desired effect.
  • Avoid probiotics in critically ill and immunocompromised patients.

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