Researchers at the University of Cambridge have identified a group of gut bacteria, named CAG-170, that turned up at higher levels in healthy people and at consistently lower levels in those living with inflammatory bowel disease, obesity, and chronic fatigue syndrome. The analysis pooled more than 11,000 gut microbiome samples from 39 countries and 13 chronic conditions, and was published in February 2026 in Cell Host & Microbe00038-7).
CAG-170 is not a household name in gut research, and that is much of the point. The bacteria have never been successfully grown in a laboratory, so standard microbiology has largely passed them by. The Cambridge group used large-scale genomic analysis to reach them anyway, sifting through thousands of microbiome samples in what is now the biggest meta-analysis of its kind.
What CAG-170 appears to do
The genomes of CAG-170 bacteria code for two things that matter for the wider gut. They produce high amounts of vitamin B12, a nutrient many other gut microbes need but cannot make themselves. And they carry enzymes that break down a broad range of carbohydrates, sugars, and dietary fibers, according to the University of Cambridge.
The researchers think the B12 mainly feeds other bacteria rather than the human host, helping to keep the wider microbial community stable. That would fit with the pattern seen in the data, where people whose gut ecosystems were out of balance, a state known as dysbiosis, also tended to have very little CAG-170.
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"Our work has revealed that CAG-170 bacteria, part of the 'hidden microbiome', appear to be key players in human health, likely by helping us to digest the main components of our food and keeping the whole microbiome running smoothly," said Dr. Alexandre Almeida of the University of Cambridge's Department of Veterinary Medicine, who led the study.
A signal across 39 countries
The consistency of the signal is what makes the finding stand out. Across very different diets, geographies, and disease groups, CAG-170 kept showing up more often in the healthy participants. The comparison groups included people with Crohn's disease, colorectal cancer, Parkinson's, and multiple sclerosis, as reported by ScienceDaily.
Almeida described the pattern in blunt terms. "We looked at the gut microbes of thousands of people across 39 countries and 13 different diseases including Crohn's and obesity. We consistently found that people with these diseases had lower levels of CAG-170 bacteria in their gut," he said.
This is an association, not proof of cause. The study cannot show whether low CAG-170 helps drive illness, whether illness depletes the bacteria, or both. But the reproducibility of the pattern across so many populations is unusual for microbiome research, where findings often fail to travel between cohorts.
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What it may mean for diet and probiotics
Because CAG-170 carries enzymes that ferment dietary fiber, the researchers see fiber-rich foods as a plausible way to support these microbes in the gut. That lines up with existing advice from public-health bodies to eat more whole grains, legumes, vegetables, and fruit, though the Cambridge team stops short of saying a specific diet will raise CAG-170 in any given person.
The commercial angle is probiotics. Today's supplements largely rely on a handful of species that were first cultured decades ago, and CAG-170 is not among them. Almeida argued that the field needs to catch up. "The probiotic industry hasn't really kept up with gut microbiome research, people are still using the same probiotic species that were being used decades ago," he said.
Turning an uncultured microbe into a next-generation probiotic will take years, and any product would need clinical testing before health claims could be made. For now, the practical takeaway is smaller. A varied, fiber-rich diet remains the best-supported way to look after the gut microbiome, and anyone with persistent gut symptoms, unexplained fatigue, or weight changes should speak with their doctor rather than reach for a supplement.
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