Updated on February 2, 2023

• Although probiotics are an appealing option to many patients struggling with IBS, there is no definitive evidence of efficacy.
• Although research into probiotics is hampered by methodological complications, research has confirmed that microbial diversity does play a role in IBS symptoms.
• With a lack of conclusive evidence supporting probiotic use, patients can explore other supplements that support microbiome health, such as butyric acid.

Probiotics have been part of the human diet for centuries, and probiotic supplements have exploded in popularity over the last few decades. Today, there are endless commercial claims about the efficacy of probiotic-rich fermented foods and probiotic supplements for gastrointestinal disorders like irritable bowel syndrome (IBS), and many are supported by patient testimonials and anecdotes from physicians. As a result, probiotics have been the subject of considerable research interest since the start of the 21st century, and interest continues to grow as alternative medicine becomes increasingly mainstream. For almost two decades, researchers have conducted rigorous in vitro experiments, animal studies, and clinical trials, to determine whether probiotics could make a difference for IBS patients.

By this point—almost two decades later—you would think the scientific community would have come to a general consensus regarding the efficacy of probiotics. However, even the briefest review of the scientific literature can leave both physicians and patients with far more questions than answers. Some individual studies show promise, while others suggest that probiotics have relatively little impact on IBS patients. Even when you turn to large meta-analyses and systematic reviews, experts in the field universally conclude that it is not clear whether or not probiotics can effectively address IBS. For practitioners and patients who are considering this body of literature, it is important to understand why no consensus has been reached, what we have found out, and what it all means for the question of whether probiotics can help IBS patients. Not only can this help patients make more informed choices regarding probiotics, it can also help them identify other supplements that can play a vital role in therapies.

Understanding the Existing Research on Whether Probiotics Help IBS

The lack of consensus on whether or not probiotics can help IBS patients is not due to an absence of research in the field. In one of the most recent systematic reviews of the potential role of probiotics in addressing IBS, published in the Journal of Infection in February 2018, researchers found more than 800 potentially relevant articles published within the last 15 years. However, despite careful analysis of hundreds of studies, the researchers could only characterize the available data as “promising” and conclude that, “further studies are needed before probiotics can be considered a reliable [therapy] for IBS.”

Other meta-analyses and systematic reviews have drawn similar conclusions. This can be frustrating for patients because these types of studies offer the highest-level evidence when it comes to determining a therapy’s efficacy. In 2017, a group of researchers from University College Cork in Ireland and Houston Methodist Hospital in Texas collaborated to discuss the inconclusiveness of several of these studies in the journal Current Medical Research and Opinion. In their critique, the authors emphasized the reason a consensus has yet to be reached: the studies that have been conducted on probiotics simply are not methodologically comparable to each other. As a result, researchers conducting meta-analyses have not been able to collect sufficient data on single therapeutic options to draw concrete conclusions.

Consider several of the common methodological distinctions between the studies that have been conducted on probiotics and IBS:

• Strain types and combinations. This is perhaps the widest source of variation between studies. Some researchers have examined the efficacy of a supplement containing only a single strain, while others have conducted studies using multiple strains in various combinations—most of which are distinct from each other.
  
• Dosage and duration of therapy. In every study, the researcher must decide how much of a probiotic the patient will take, how often they will take it, and for how long—all of which impact the finding of a single study. With so many study designs to correlate, the data becomes much more muddled, and it becomes much harder to compare studies and verify findings.
  
• Delivery method. In some studies on probiotics and IBS, the focus is on the potential efficacy of naturally probiotic-rich foods, like yogurt. In others, probiotics are formulated into functional foods or supplements, and it is not clear whether the delivery method plays a role.
  
• Measure of efficacy. There is no single scale that researchers use when characterizing the effectiveness of probiotic supplements for IBS patients. Some studies focus on specific symptoms, like bloating and abdominal pain, while others evaluate broader measures, like perceived quality of life. Even when individual symptoms are emphasized in a particular study, comparison can be difficult because the types of IBS are so varied. For instance, a patient who has IBS with Diarrhea (IBS-D) might experience positive results from a supplement that makes little difference for an individual who has IBS with Constipation (IBS-C).

Drawing Out Themes from the Existing Research Evidence

Although the heterogeneity of studies on probiotics and IBS makes it difficult for researchers to draw conclusions on the broad question of whether probiotics help patients with IBS, there is one clear area of consensus: that this research is worthwhile. It is becoming increasingly clear that microbial diversity does play a role in the pathophysiology of IBS, which provides a strong theoretical foundation for the idea that probiotics might help resolve symptoms. Although no clear, universal pattern of change in the microbiome has been identified, the latest research suggests that both the diversity and the abundance of bacterial strains in the gut varies between IBS patients and the general population.

Moreover, there are certain themes that the evidence presents, even by researchers who are most concerned about the heterogeneity of the existing research literature. Specifically, it appears that probiotic bacteria from the genus Bifidobacterium have the largest beneficial impacts on IBS patients. Some researchers go so far as to specifically highlight B. infantis as the best-supported strain, while others continue to reserve judgment, holding out for more comprehensive studies in the future. However, it is important to recognize this is not the only bacterial strain implicated in IBS studies, so patients might still experience strains in other genera to be effective.

Considering Probiotic Therapy Options

Ultimately, answering the question of whether probiotics can help IBS patients is more complicated than it seems. Although for the research community, the jury is still out, patients and practitioners can still act on the available evidence. Knowing that scientists agree that the microbiome is involved in the pathophysiology of IBS, it might be valuable to try a probiotic supplement or another supplement that is associated with microbiome function, such as butyric acid. The diversity of IBS studies also indicates that results can vary depending on factors like the bacterial strain, dosage, and type of IBS, so patience is dictated for both physicians and patients looking for an optimal therapy to meet unique needs.

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Works Cited

Allen AP, Clarke G, Cryan JF, et al. 2017. Current Medical Research and Opinion. 33(7):1349-51.

Aragon G, Graham DB, Borum M, Doman DB. 2010. Gastroenterology and Hepatology. 6(1):39-44.

Mazurak N, Broelz E, Storr M, Enck P. 2015. Journal of Neurogastroenterology and Motility. 21(4):471-85.

Ozen M, Dinleyici EC. 2015. Beneficial Microbes. 6(2):159-65.

Pozuelo M, Panda S, Santiago A, et al. 2015. Scientific Reports. 5:12693.

Principi N, Cozzali R, Farinelli E, et al. 2018. Journal of Infection. 76(2):111-20.