Irritable Bowel Syndrome and microbiota: is there a link?

How many people suffer from IBS?

Prof. Premysl Bercik: Data differ between countries, but it is estimated that IBS affects around 5 to 10% population globally. ² Women are almost twice as likely as men to have IBS. They also report more fatigue and psychological distress. For both men and women, IBS can develop at any age, but its onset is often between age of 20 and 30.

The quality of life of IBS patients is severely affected, interfering with their everyday life, frequently resulting in missing work or school. ³

What triggers IBS symptoms? Why do I develop IBS?

P.-B.: IBS is a complex disorder, its genesis is likely multifactorial and not fully understood. In general, it stems from impaired gut–brain interaction, a bidirectional communication between the digestive tract and the central nervous system. There are several peripheral mechanisms involved in IBS, including intestinal hypersensitivity, altered bowel motility, increased intestinal permeability and low-grade inflammation. In the brain, the signals from the bowel may be incorrectly interpreted and further magnified, and then the brain sends erroneous signals to the gut. During the last decade, increasing attention has been given to gut microbiota as a key player in IBS ^4,5.

What is the scientific evidence for the involvement of the gut microbiota in IBS?

P.-B.: There are several lines of evidence that implicate microbiota in IBS:

• First, bowel infection (gastroenteritis) is the strongest risk factor for IBS, with 11-14% of patients developing chronic symptoms after acute infection with pathogenic bacteria (Salmonella, E. coli or Campylobacter infection). ⁶
• Second, clinical studies showed that microbiota-directed treatments affect IBS symptoms. Indeed, certain antibiotics improve symptoms in some patients with IBS, while in asymptomatic individuals they can trigger IBS symptoms. Specific probiotics were shown to improve symptoms of IBS, such as abdominal pain, diarrhea or bloating, although there is currently no consensus on which probiotics to recommend in clinical practice. ²
• Third, gut microbial composition and metabolic activity differ between IBS patients and healthy individuals, and associate not only with bowel symptoms, but also with anxiety and depression. However, the results from individual studies vary and there seems to be no unique microbial profile that could be attributed to IBS. ⁷
• Finally, and most importantly, several studies have shown that gut dysfunction and associated anxiety can be transferred through microbiota transplantation from IBS patients into germ-free mice. ^8,9,10

You’ve talked about gut-brain interaction. Is there a microbiota-gut-brain axis?

P.-B.: The gut-brain axis involves immune, neural and hormonal signaling and growing evidence suggests that the gut microbiota plays a key role in this communication. Although most data have been obtained from animal studies, many clinical studies support this concept. ¹¹ Just to mention few, sudden changes in behavior have been described in patients treated with antibiotics. A recent population-based study found that use of antibiotics in early childhood is associated with an increased risk of developing mental health disorders in later life. The most obvious case comes from patients with end-stage liver disease (cirrhosis), diagnosed with hepatic encephalopathy. (sidenote: Hepatic encephalopathy (HE) Hepatic encephalopathy (HE) refers to changes in the brain that occur in patients with advanced, acute (sudden) or chronic (long-term) liver disease. It is one of the major complications of cirrhosis. https://britishlivertrust.org.uk/information-and-support/living-with-a-liver-condition/liver-conditions/hepatic-encephalopathy/ ) These patients display altered behavior and cognition which improve quickly and dramatically after administration of antibiotics or laxatives, or fecal microbiota transplantation ¹². And multiple studies found that the microbial profiles differ between patients with psychiatric disorders and healthy individuals. ¹³

Can we modulate the gut microbiota to improve mental health?

P.-B.: In animal models, certain probiotics have shown beneficial effects on behavior and brain chemistry, suggesting they could be used therapeutically in mental disorders. The results of the few clinical studies completed so far suggest that probiotics, if used as an adjunctive treatment, improve symptoms in patients with major depressive disorder. ¹³ And our recent pilot study found that probiotic treatment improved depression scores and bowel symptoms in patients with IBS, and changed their brain activation patterns. ¹⁴ Altogether, this suggest that some probiotics could be helpful not only for patients with functional bowel disorders, but also for those with mental health issues. However, this needs to be confirmed by larger rigorous clinical studies.

^BMI-23.14