IBS

Not all IBS is the same, in the gut

IBS is common. Depending on how it's counted, it affects an estimated 4% to 9% of people worldwide. Researchers have found it isn't one single condition at the gut bacteria level. One study looked closely at the bacteria of people with IBS. About half had a gut bacteria pattern that looked different from a healthy person's, a pattern researchers called "pathogenic." The other half had a gut bacteria pattern that looked similar to a healthy person's, even though they still had IBS symptoms. A separate study looked at many people with IBS and found a shared pattern too. People with IBS tended to have more of two bacteria groups, Enterobacteriaceae and Lactobacillaceae. They also tended to have more of a third, Bacteroides. At the same time, they had less of two other groups, Faecalibacterium and Bifidobacterium, bacteria already linked elsewhere to gut health benefits.

Source: Gut, Two microbiota subtypes identified in irritable bowel syndrome with distinct responses to the low FODMAP diet

Source: Microbiota Institute, Microbiota gut-brain axis in Irritable Bowel Syndrome

A stomach bug can trigger it for good

One of the clearest signs that the gut is really behind IBS comes from what happens after a stomach bug. Some stomach bugs are caused by bacteria, not viruses. After one of these bacterial infections clears up, some people don't fully recover. Between 11% and 14% of people go on to develop long-term IBS symptoms afterwards. Researchers see this as one of the strongest risk factors for IBS found so far.

Diet changes the gut, and it depends who you are

In the study above, the two groups responded differently to diet. People with the "pathogenic" gut pattern responded much better to a low FODMAP diet than people with the healthier-looking pattern. A low FODMAP diet is a diet that cuts out certain hard-to-digest carbohydrates for a while. Their gut bacteria shifted too, moving closer to a typical healthy pattern. A separate trial tested three things on 73 people with IBS: a low FODMAP diet on its own, probiotics on their own, and both together. After four weeks, symptoms improved in every group. Diet alone improved symptoms by around 40%. Probiotics alone improved symptoms by around 55%.

Source: Journal of Digestive Diseases, Effect of the combined intervention of low-FODMAPs diet and probiotics on IBS symptoms

Transplanting gut bacteria directly, with mixed results

Researchers have also tested a more direct approach. In one trial, people with a diarrhoea-type of IBS received a faecal microbiota transplant, or FMT. This means a small amount of stool from a healthy donor is placed into someone else's gut, to introduce healthy bacteria. Some patients received FMT on its own. Others received FMT alongside a low FODMAP diet. The combined group did better at every check-in. At one month, 70% of the combined group improved, compared with 55% of the FMT-only group. At six months, 62.5% of the combined group were still doing better, compared with 27.5% of the FMT-only group.

But it's important to be honest here. A separate trial tested FMT delivered in a capsule instead. In that trial, the result was the opposite. People given a fake, placebo capsule actually felt better than people given the real FMT capsule. This means FMT for IBS is still an unsettled area. It works well in some trials and poorly in others.

Source: Fecal Microbiota Transplantation Combined with a Low FODMAP Diet for the Treatment of Irritable Bowel Syndrome with Predominant Diarrhea

Source: Gut bless you: The microbiota-gut-brain axis in irritable bowel syndrome

What this means for you

Persistent pain, bleeding, or unexplained weight loss need a doctor's assessment first, to rule out other causes before assuming it's IBS. A low FODMAP diet works best with guidance from a dietitian, since it means cutting out several common foods for a while before slowly reintroducing them. Alongside that, building back a wider variety of plant foods over time supports the same kind of gut shift the research above measured. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.