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Probiotics have increased in popularity in the past few years. According to a survey by the National Center for Complementary and Integrative Health, about 4 million US adults (1.6% of the population) used a probiotic or prebiotic supplement in the past 30 days¹. From grocery store aisles devoted to probiotics to social media influencers, there are claims for probiotics, including improvement of everything from constipation to obesity to depression. What is the evidence that probiotics promote health?

Probiotics are gut microorganisms that are helpful in digesting food, producing vitamins, and fighting harmful pathogens. Probiotics are found in naturally fermented foods like yogurt, cheese, and kombucha.  The products we are addressing consist of similar bacteria, commercially manufactured and distributed. 

There is experimental evidence that probiotics can alleviate symptoms of Inflammatory Bowel Syndrome (IBS).  People taking a probiotic with the bacteria Bifidobacterium bifidum MIMBb75 experienced less discomfort, bloating, urgency, and digestive disorder compared to those who took a placebo².

The evidence that probiotic use is helpful for restoring healthy gut flora after a course of antibiotics includes genetic sequencing of stool samples demonstrating increased diversity of gut bacteria and fewer antibiotic-resistant bacteria³.

There is some evidence of a connection between the gut microbiome and the brain. In one study, people with IBS taking the probiotic Bifidobacterium longum NCC3001 had fewer symptoms of depression relative to people taking a placebo⁴.  They also had reduced brain activity on fMRI in response to negative stimuli. More experimental evidence is needed to confirm these relationships. 

There are case reports of sepsis or fungemia from bacteria⁵ or yeast⁶ in probiotics in people with immune system deficiencies. However, the potential for harm is low, and no serious adverse events were reported in clinical trials. The most common side effect for the average healthy person is temporary bloating and constipation, which typically subsides after a few weeks of use⁷.

Think twice before consuming a probiotic pill. A healthy diet including natural sources of gut flora is probably just as good as any pill or drink. We need more experimental evidence before we can be certain of the relative potential benefits and harms of probiotics, natural or in pill form, for various illnesses.  

1. https://www.nccih.nih.gov/research/13-year-trends-for-complementary-approaches-where-questions-are-very-similar-across-years
2. https://pubmed.ncbi.nlm.nih.gov/21418261/
3. https://pubmed.ncbi.nlm.nih.gov/26395781/
4. https://www.gastrojournal.org/article/S0016-5085(17)35557-9/fulltext
5. https://www.clinicalmicrobiologyandinfection.com/article/S1198-743X(14)61883-8/fulltext
6. https://www.sciencedirect.com/science/article/pii/S2211753917300441?via%3Dihub
7. https://www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/whats-the-deal-with-probiotics#:~:text=There%20is%20no%20clear%20evidence,the%20results%20of%20different%20studies