Stomach pain, flatulence, bloating, discomfort. These are just some of the symptoms of Irritable Bowel Syndrome (IBS), a chronic condition affecting more than 10% of the population with highest impact in women. Treatment cannot cure the condition, only alleviate the symptoms. Its origin is unknown, although increasingly more researchers suspect that imbalances in the gut microbiota may play a major role in its development.

“We do not, currently, have any biomarkers for diagnosing the condition. Doctors can only rely on symptoms to diagnose and prescribe treatment to relieve the most obvious ones,” says Chaysavanh Manichanh, who leads the Metagenomics Laboratory at the Vall d’Hebron Research Institute (VHIR) in Barcelona.

But what if the bacteria that inhabit the gut could be used to diagnose the condition and treat it in the most suitable way? Manichanh and her team carried out a study with 113 people suffering from irritable bowel and 66 healthy individuals. Three patient sub-types were included in the first group – those suffering from diarrhoea, those with chronic constipation and those who alternate diarrhoea with constipation. In total, a metagenomic analysis of the microbiome of 273 faecal samples was carried out.

“Our results show that people with IBS with diarrhoea have a different microbiota to those with constipation. We have even found which bacteria groups vary between some patients and others,” the researcher explained to

The study, published in Nature Scientific Reports, concludes that people with IBS with constipation have a similar gut microbiota composition to the healthy volunteers, while the same composition is very different to those with diarrhoea or those who alternate between diarrhoea and constipation.

“We have seen that the subjects with diarrhoea suffer a greater loss of bacterial diversity in comparison with the other groups. And that loss correlates with the bacteria responsible for producing butyrate and methane,” says Manichanh.

Specifically, butyrate is known to contribute to the impermeability of the gut’s epithelial barrier, which means that when the bacteria in charge of producing this are missing or sparse, it is easier for the gut’s microbes to penetrate the barrier and interact with immune or nerve cells in the gut wall. With methane, scientists have not only identified that patients with diarrhoea have less microbes that produce the gas, but that these kind of bacteria that are associated with slowed gut transit, abound in patients with constipation.

The next step, says Manichanh, will now be to design new experiments with a larger group of patients in order to confirm these results and also isolate the bacteria identified and determine that they are key mechanisms in the different subtypes of IBS (or biomarkers for the condition). If this were achieved, they would be able to start a clinical trial in order to trace the bacterial profile or the bacteria involved in the disease and apply a specific treatment to each group of patients.

Next year, they plan to begin a study to try and modulate the gut microbiota through diet. “We know that what we eat has an impact on bacterial composition. People who eat more vegetables, for example, have a greater amount of Prevotella, while those who eat more meat have more Bacteroides. We will propose a series of questionnaires to healthy volunteers and patients in order to find out what their diet is like and we will then analyse their microbiota to see if there is a correlation,” explains the VHIR researcher.