For a long time, irritable bowel syndrome (IBS) was poorly understood. Diagnosing it is mostly about tests to eliminate other potential causes for the symptoms, which include abdominal cramps, bloating, constipation and diarrhoea. Treatments are still limited.
Part of the problem has always been that, on the face of it, there appear to be no medical reasons for the gastrointestinal problems that IBS sufferers experience.
“There are a variety of gut conditions where you can see inflammation when tests are done but with irritable bowel syndrome the intestine looks normal,” explains Professor Stuart Brierley, an expert in gastrointestinal neuroscience at the South Australian Health and Medical Research Institute. “So, the question is, what is causing the chronic pain and other symptoms?”
IBS is now being recognised as a disorder of gut-brain communication and researchers believe it may be triggered initially by some sort of stomach bug, perhaps an E. coli or salmonella infection, or a norovirus, and that the balance of the microbiome (the colony of bacteria that lives in our gut) plays a role.
Now, in a study using mice, Brierley and his team have had a breakthrough, identifying the pathway linking the gut and brain that is involved with IBS.
“Our study shows that the microbiome produces chemicals called short-chain fatty acids,” explains Brierley. “They act on a particular type of cell within the lining of the gut wall called the enterochromaffin cell. It only represents about 1 to 2% of all the cells within the intestinal lining but sits there on alert looking for certain things. When it detects them, it releases various substances which then act on the nerves. That helps drive the pain signal.”
Once this mechanism is activated, it can also communicate with anxiety pathways – Brierley describes the process as being like sensory overload.
And gut-brain communication works both ways, so the brain is sending signals back to the gut, which explains why stress can trigger IBS symptoms or make them worse.
“It’s really about having a balance in the way the system operates, and if you are out of balance, then you end up having a problem,” says Brierley. “For these patients, it can be a downward spiral; the longer they suffer from chronic pain, the worse the anxiety and depression get.”
While it is normal to produce short-chain fatty acids, possibly the microbiomes of IBS sufferers are making too many of them or something else is out of kilter.
We know that IBS is more common in women than men and the study seems to have uncovered a reason for this.
“What we found with this mechanism is that if we were looking at males, then we could activate this pathway with short-chain fatty acids and induce pain and anxiety,” explains Brierley. “But in females, the pathway already seemed to be activated. So, in simple terms, that means it is much closer to being near the threshold for pain and anxiety, and it takes a smaller amount to tip it over the edge.”
Researchers are now trying to get a greater understanding of the pathway in the hope of developing ways to block communication and so stop gut pain at the source and reduce anxiety. Future interventions are likely to include medications and microbiome and diet-based treatments.
In the meantime, Brierley urges anyone experiencing IBS-type symptoms to see a doctor and be referred to a gastroenterologist in order to rule out other conditions.
“It’s really important to get an accurate diagnosis before you start to think about treatments or changes in diet,” he says. “A variety of things may help. If someone has had a gut infection then an antibiotic may be appropriate. Antihistamines might be useful as it has been shown you can get an activation of mast cells [a type of white blood cell that is a key player in the inflammatory response], which trigger symptoms.”
Low-Fodmap diets, which restrict fermentable carbohydrates, have been shown to reduce digestive problems, and some people with IBS may also have an underlying food allergy that triggers symptoms.
Normalising the microbiome, via a faecal transplant, also appears to be a promising treatment.
