A global study of over 11,000 people across 39 countries has identified a mysterious group of gut bacteria called CAG-170 that appears far more often in healthy individuals and significantly less common in people with chronic diseases. This discovery could fundamentally change how scientists measure what a truly healthy microbiome looks like and may lead to more targeted probiotic approaches in the future .

What Is CAG-170 and Why Does It Matter?

CAG-170 is a group of gut bacteria known only through its genetic signature. Scientists have not yet been able to grow most of these bacteria in laboratory settings, which has made them difficult to study directly until now. Researchers at the University of Cambridge used advanced computational techniques to search for CAG-170's genetic fingerprint in gut microbiome samples from more than 11,000 people living primarily in Europe, North America, and Asia .

The pattern was striking and consistent across all countries studied. Healthy individuals had significantly higher levels of CAG-170 compared to people diagnosed with 13 different chronic diseases, including inflammatory bowel disease, obesity, chronic fatigue syndrome, Crohn's disease, colorectal cancer, Parkinson's disease, and multiple sclerosis .

Further genetic analysis revealed that CAG-170 has the ability to produce large amounts of vitamin B12 and carries enzymes that help break down carbohydrates, sugars, and fibers in the gut. Researchers believe the vitamin B12 produced by CAG-170 likely supports other beneficial gut bacteria rather than directly benefiting the person hosting it, suggesting these microbes help maintain balance within the broader gut ecosystem .

How Did Researchers Uncover This Hidden Microbiome?

This groundbreaking discovery builds on earlier work by Dr. Alexandre Almeida and his team to assemble a detailed reference library of microbial genomes found in the human gut. That resource, known as the "Unified Human Gastrointestinal Genome catalogue," maps the genetic blueprints of microbes that live inside us. To create the catalogue, researchers used a technique called metagenomics, which involves analyzing all microbial DNA in a gut sample at once and then separating it into individual species .

The work identified more than 4,600 bacterial species living in the gut. Remarkably, more than 3,000 of these had never been documented there before, highlighting how much of the microbiome remains unexplored and underappreciated. These reference genomes act like genetic fingerprints that allow researchers to detect specific microbes in other gut samples .

"Our earlier work revealed that around two-thirds of the species in our gut microbiome were previously unknown. No-one knew what they were doing there, and now we've found that some of these are a fundamental and underappreciated component of human health," explained Dr. Alexandre Almeida, a researcher in the University of Cambridge's Department of Veterinary Medicine.

Dr. Alexandre Almeida, Department of Veterinary Medicine, University of Cambridge

What Did the Three-Part Analysis Reveal?

The research team conducted three independent analyses to confirm their findings. In the first analysis, they compared more than 11,000 gut microbiome samples to the Unified Human Gastrointestinal Genome catalogue and found that CAG-170 stood out as the group within the hidden microbiome most strongly associated with good health. This pattern was consistent across all countries studied .

In a second analysis, scientists examined the full gut microbiome composition of more than 6,000 healthy individuals to identify which species appeared most capable of stabilizing the gut ecosystem. Once again, CAG-170 ranked as the group most consistently linked to health .

A third analysis focused on people with dysbiosis, a condition in which the gut microbiome becomes imbalanced. Lower levels of CAG-170 were associated with a greater likelihood of dysbiosis, which has been linked to long-term conditions such as irritable bowel syndrome, rheumatoid arthritis, and anxiety and depression .

How Does Gut Health Connect to Brain Aging?

Beyond the CAG-170 discovery, emerging research reveals that the gut microbiome plays a surprisingly direct role in brain health and cognitive aging. Researchers at Stanford Medicine and the Arc Institute found that the timeline of memory decline is not hardwired but is actively modulated by the body, with the gastrointestinal tract serving as a critical regulator of this process .

Scientists examined the gut microbiome in older mice and found that it changes with age. In older mice, certain groups of bacteria become more common, and these changes are detected by immune cells in the gut, which trigger inflammation. This disrupts communication between the gut and the brain, making it harder for the vagus nerve to send signals to the hippocampus, the region responsible for memory .

When researchers stimulated the vagus nerve in older mice, memory improved significantly; the animals were able to recognize new objects and navigate mazes just as well as younger mice. This suggests that protecting memory may not require focusing solely on the brain itself but rather on maintaining a healthy gut composition .

"We tend to think of memory decline as a brain-intrinsic process. But this study indicates that we can enhance memory formation and brain activity by changing the composition of the gastrointestinal tract, a kind of remote control for the brain," stated Christoph Thaiss, PhD, assistant professor of pathology at Stanford Medicine.

Christoph Thaiss, PhD, Assistant Professor of Pathology, Stanford Medicine

Ways to Support a Healthy Gut Microbiome

While CAG-170 bacteria cannot yet be cultured in the laboratory, researchers are working toward developing new methods to grow and test them before these findings can lead to potential new therapies. In the meantime, experts suggest several approaches to support overall gut health based on current microbiome research:

• Dietary Fiber Intake: Consuming foods rich in prebiotic fiber helps feed beneficial bacteria in the gut, supporting the broader microbial ecosystem that CAG-170 appears to maintain.
• Diverse Plant Foods: Eating a variety of plant-based foods promotes microbial diversity, which research suggests is associated with better health outcomes and resilience against dysbiosis.
• Monitoring Gut Health Markers: As CAG-170 becomes better understood, it may eventually serve as a marker of gut microbiome health, allowing people to track their microbial balance through advanced testing.

What Does This Mean for the Future of Probiotics?

The probiotic industry has historically focused on bacteria that can be easily grown and studied in laboratory settings. However, this new research suggests that approach may be limiting. Most CAG-170 bacteria cannot yet be cultured in the lab, which has prevented them from being included in traditional probiotic formulations .

"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. We're now discovering new groups of bacteria like CAG-170 with important links to our health, and probiotics aimed at supporting them could have a much greater health benefit," noted Dr. Almeida.

Dr. Alexandre Almeida, Department of Veterinary Medicine, University of Cambridge

The findings suggest that CAG-170 could eventually serve as a marker of gut microbiome health and point toward the possibility of developing probiotics designed specifically to maintain healthy levels of these bacteria. However, scientists will need to develop new methods to grow and test CAG-170 before these findings can lead to potential new therapies .

This research represents a significant step forward in understanding what a truly healthy microbiome looks like. By better defining healthy microbiome composition, researchers can identify how it changes in disease and potentially restore balance through more targeted interventions. The discovery of CAG-170 and the broader exploration of the hidden microbiome suggest that the next generation of microbiome-based health strategies will be far more sophisticated and personalized than current approaches .