A Closer Look at the Role of the Microbiome in IBS

A Closer Look at the Role of the Microbiome in IBS

By: Desiree Nielsen

A Closer Look at the Role of the Microbiome in IBS

Irritable bowel syndrome, with its constellation of symptoms and potential causes, is far more than a bit of stomach upset. As a disorder of gut-brain communication, IBS offers an important example of the complex interactions between the digestive, immune and nervous systems.1

It is impossible to talk about IBS without talking about the gut microbiota, which lies at the intersection of the gut-brain-immune connection. Early research suggests that the gut microbiota of those with IBS is different from those without the condition; however, the research has yet to establish a definitive ‘fingerprint’ of the IBS microbiota.1,2 Knowing this, it is reasonable to expect that the trillions of microbes that live in the gut are an important root cause of IBS symptoms…but what does the research say? Let’s examine the role of the microbiota along the entire spectrum of risk factors to treatment.


Microbiota as a risk factor for IBS

Risk factors for IBS are well understood and include early life stressors, enteric infection and exposure to antibiotics; interestingly, all three of these risk factors could be reasonably expected to alter the gut microbiome.1-3 Stress is well-known to alter the gut environment and its microbiota–in fact, stress is enough to exacerbate IBS once it exists.4,6 Enteric infection is a well-defined risk factor for irritable bowel syndrome. Alterations post-infection can lead to a subcategory of IBS known as post-infectious IBS. 

Perhaps the most intriguing connection is that antibiotics in early life are a risk factor. There remains some controversy over the plasticity of the gut microbiota post-antibiotic use. While some research suggests that the microbiota bounces back relatively quickly post-treatment, others suggest that a single course of antibiotics can alter the microbiota for months, allowing opportunistic pathogens to gain a foothold.7,8 That exposure to these routine alterations could be linked to the development of irritable bowel syndrome later on suggests that even subtle insults could lay the groundwork for a less resilient microbiome that can place digestive health at risk.


Microbiota in symptoms of IBS

Irritable bowel syndrome symptoms can range from mild to severe and include diarrhea or constipation, abdominal pain, along with increased gas and bloating. These symptoms can make everyday activities such as commuting to work more challenging, with a negative impact on quality of life. The nervous system is a primary driver, along with potential roles for the immune system and the microbiota.

Let’s take a look at two primary IBS symptoms–altered motility and visceral hypersensitivity–that originate in the nervous system. Interestingly, the microbiota have been found in the research to impact both.

Localized mucosal inflammation is known to sensitize the nervous system, with the potential to increase pain perception.4 It is suggested that gut barrier alterations in IBS may contribute to nervous system changes; gut barrier integrity is critical to maintaining a calm immune response.4,6 Inflammation can occur due to concurrent disease states, infection, dietary choices or food allergy as well as bacterial imbalances.4,6 Certain strains of bacteria, such as those from Pseudomonas or Ruminococcus species, can alter barrier function in such a way to activate the inflammatory response while the inflammatory response can alter the gut microbiota itself creating the potential for a self-sustaining feedback loop.6

The gut microbiota also has the potential to influence the enteric nervous system directly, through short chain fatty acids, which may influence local neurotransmitter production.5 Finally, it is well established that enteric infection can alter stool quality with respect to diarrhea; however, can microbes impact constipation? The answer is yes. It is thought that methanogens, which are in fact not bacteria but hail from the domain Archaea, are associated with increased rates of functional constipation and delayed transit time in IBS.15

In the literature, there are countless associations between the gut microbiota and potential origins of irritable bowel syndrome; however, there is a lot more to understand before some of this knowledge can change clinical practice. In the meantime, it makes sense that our gut microbiota be addressed while treating irritable bowel syndrome as long as we are aware of the potential limitations of this approach.


Microbiota in IBS Management

There are two major routes to altering the microbiota: influencing its composition with probiotics or with food substrates. 

Initially, research focused on the potential of prebiotic substances such as inulin to positively influence the gut microbiota; however, in irritable bowel syndrome, it is the opposite approach that has been found useful. The low FODMAP exclusion diet omits fermentable carbohydrates that drive growth in the gut microbiota, providing symptom relief rates of approximately 50-87%.9,10 While not a great deal of research exists, what is currently known is that the low FODMAP diet decreases both the richness and diversity of the gut microbiota–which is why the diet is not recommended as a long term solution.9,10 That is helps provide symptom relief alongside altering the gut microbiota suggests that its effect on the gut microbiota at least contributes to symptom experience.

With respect to probiotics, a large body of literature exists examining the role of probiotics in providing symptom relief in IBS. The research suffers from heterogeneity, however, systematic reviews suggest that multi-strain probiotics may hold potential.3,11,12 And there are examples of specific retail probiotics that have shown benefit, including Bio-K+ probiotics. In 2018, one trial of 113 people with IBS found that IBS is effective at reducing the number of high pain days, improving the consistency and frequency of stool, as well as quality of life* for those with IBS-D.13,14


Taking an integrative approach to IBS

As a dietitian, it is important to know that nutrition is an important part of managing IBS–but it is not a standalone option. As a disorder of gut-brain communication, addressing stress management is critical–as is acknowledging the role of the microbiome in the natural history of the condition. In my practice, we take an integrative approach that includes dietary change, stress management, physical activity and a probiotic such as Bio-K+ IBS Control. 




* IBS-QoL included an overall score and assessment of quality of life in eight validated domains: dysphoria, interference with activity, body image, health worry, food avoidance, social reaction, sexual, and relationship. 



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