According to research reviewed by Gram, a gut bacterium called Ruminococcus gnavus is linked to high cholesterol. In a 2026 study, people with high cholesterol carried more of this bacterium, which converted a bile acid into a compound called isoCDCA. In a separate group of 1,137 people, higher isoCDCA levels were linked to higher cholesterol.
According to research reviewed by Gram, a gut bacterium called Ruminococcus gnavus may play a role in high cholesterol. Researchers found that people with high total and LDL cholesterol carried more of this bacterium in their stool, whether or not they were overweight. The team confirmed this pattern in a separate group of 488 people. When they gave the bacterium to mice, the animals developed changes in their blood fats and liver health, including fat buildup in the liver. The bacterium appeared to convert a bile acid into a compound called isoCDCA, which also raised blood fats in mice. In a group of 1,137 people, higher isoCDCA levels were linked to higher cholesterol, triglycerides, and LDL cholesterol. These findings are early and mostly come from animal and lab studies, so they do not yet show that the bacterium causes high cholesterol in people. Still, they point to a possible new target for preventing and treating high cholesterol.
Key Statistics
A 2026 study published in Gut Microbes found that Ruminococcus gnavus was more common in people with high cholesterol, and this pattern was confirmed in an independent group of 488 people.
A 2026 study of 1,137 people found that higher blood levels of the bile acid derivative isoCDCA were positively associated with total cholesterol, triglycerides, and LDL cholesterol.
A 2026 mouse study published in Gut Microbes found that giving mice isoCDCA by mouth reproduced key blood fat disturbances, suggesting the compound may play a direct role in lipid changes.
The Quick Take
- What they studied: Researchers wanted to know whether a specific gut bacterium, Ruminococcus gnavus, contributes to high cholesterol, and if so, how it does so.
- Who participated: The researchers compared people with high cholesterol to people with normal cholesterol, including both normal-weight and overweight adults. A separate group of 488 people was used to confirm the bacteria findings, and another group of 1,137 people was used to measure a bile acid in the blood. Mice were also used to test the effects directly.
- Key finding: People with high cholesterol had more of this bacterium in their stool, and they had higher blood levels of a compound called isoCDCA. In mice, the bacterium and isoCDCA both led to higher blood cholesterol and fat buildup in the liver.
- What it means for you: This research does not yet prove that gut bacteria cause high cholesterol in people. It does suggest that gut health may someday be part of how doctors prevent or treat high cholesterol. For now, standard steps like a heart-healthy diet, regular activity, and talking with your doctor about cholesterol testing remain the best approach.
The Research Details
The study started by looking at the gut bacteria of people with high cholesterol and comparing them to people with normal cholesterol. The researchers included both normal-weight and overweight adults so they could see whether body weight changed the results. The bacterium that stood out, Ruminococcus gnavus, was then checked in a second, independent group of 488 people using a lab test that detects specific bacteria.
Next, the team tested the idea in mice. Some mice ate a normal diet and others ate a high-fat diet. Researchers gave some of the mice this bacterium and then measured their blood fats, liver health, and the genes active in their livers. They also tested the bacterium in lab dishes to see whether it could change a bile acid, a digestive substance made from cholesterol, into a different compound called isoCDCA.
Finally, the researchers measured isoCDCA in the blood of 1,137 people and checked whether it matched cholesterol levels. They also fed isoCDCA to mice and used genetically modified bacteria to see whether the bacterial enzymes were responsible for making the compound. Each step tested a different link in the chain.
Combining people, mice, and lab experiments helps show whether a finding holds up across different settings. Studies in people can show a link, while mouse and lab studies can test whether one thing actually leads to another. This mix of methods makes the proposed chain of events more convincing than any single approach could.
The study used several large groups of people and checked its main finding in a separate group, which adds confidence. Its use of genetic tests, direct feeding experiments, and lab work strengthens the case for a biological mechanism. However, most of the strongest proof comes from mice and lab cells, not from a trial in people. Human data in this study are observational, which means they show associations rather than cause and effect. Readers should view the findings as promising rather than settled.
What the Results Show
The researchers found that Ruminococcus gnavus was more common in people with high total cholesterol or LDL (“bad”) cholesterol. This pattern held for both normal-weight and overweight people, which suggests the link is not just due to body weight. The finding was then confirmed in a separate group of 488 people, which makes the result more trustworthy.
In mice, giving the bacterium changed blood fat levels and liver function markers. Mice also developed fat buildup in the liver, a condition called hepatic steatosis. The animals showed changes in several liver genes involved in cholesterol and fat handling, including genes that help the body make bile acids and clear LDL cholesterol from the blood.
The team also found that the bacterium converted a bile acid called chenodeoxycholic acid (CDCA) into isoCDCA, both in the animals and in lab dishes. When mice were given isoCDCA by mouth, they developed many of the same blood fat problems. In the cells of the liver, isoCDCA also turned down genes that control fat processing and encouraged fat to build up inside liver cells.
In the group of 1,137 people, higher blood levels of isoCDCA were found in those with high cholesterol. Within this group, isoCDCA levels were positively associated with total cholesterol, triglycerides, and LDL cholesterol. This means the two tend to rise together, though this kind of study cannot prove that isoCDCA is what causes the rise.
The researchers also engineered other bacteria to carry the enzymes from Ruminococcus gnavus that make isoCDCA. When these engineered bacteria were placed in mice, the animals had higher total and LDL cholesterol. This step is important because it suggests the enzymes themselves, not just the whole bacterium, may be responsible for the effect. It also points to specific molecules that could be studied as future treatment targets.
Scientists have long known that gut bacteria can influence how the body handles fats and cholesterol, and that bile acids act as signals in this process. This study adds a specific bacterium and a specific bile acid product to that picture. It fits with earlier work suggesting that changes in gut bacteria may affect heart disease risk, but it goes further by tracing a particular chain of events from microbe to liver.
Most of the detailed proof comes from mice and laboratory experiments, and mice do not perfectly match human biology. The human studies were observational, so they cannot show whether the bacterium causes high cholesterol or whether high cholesterol changes the gut. Diet, medications, and other health factors can also affect both gut bacteria and cholesterol, and it is hard to fully account for them. The study also does not show how much isoCDCA or this bacterium would need to change to make a meaningful difference for people. More research in humans, including trials that test changes to gut bacteria directly, is needed before these findings can guide treatment.
The Bottom Line
Based on this early research, there is not yet enough evidence to recommend any change to treatment or diet specifically for Ruminococcus gnavus or isoCDCA. Confidence is low to moderate that this bacterium plays a role in cholesterol, since the link is strong in animals and in the lab but only observed in people. Proven steps for lowering cholesterol, such as eating more fiber and vegetables, limiting saturated and trans fats, staying active, and following your doctor’s advice, remain well supported.
People with high cholesterol, families with a history of heart disease, and researchers studying gut health may find this research especially interesting. People already taking cholesterol medication should keep taking it as prescribed and should not change their treatment based on this study. Children, pregnant people, and anyone with a complex medical condition should speak with a doctor before making any changes based on new research.
This research is at an early stage, so practical treatments based on it are likely years away. Scientists would first need to confirm the findings in larger human studies, then test whether changing gut bacteria or blocking isoCDCA can actually lower cholesterol safely. Any real benefit would likely take many years of further research to show.
Frequently Asked Questions
Can gut bacteria cause high cholesterol?
Early research suggests gut bacteria may contribute to high cholesterol. A 2026 study found Ruminococcus gnavus more often in people with high cholesterol, and mouse experiments linked it to higher blood fats. Human cause and effect has not been proven yet.
What is isoCDCA and how does it relate to cholesterol?
isoCDCA is a compound made when a gut bacterium changes a bile acid. In a study of 1,137 people, higher isoCDCA levels were associated with higher cholesterol and triglycerides. Mice given isoCDCA developed similar blood fat changes, though more research is needed.
Should I change my diet because of this gut bacteria research?
Not based on this study alone. The findings are early and come mostly from mice and lab work. Eating more fiber, vegetables, and whole grains while limiting saturated fat is well supported for lowering cholesterol. Discuss any changes with your doctor.
Could future treatments target gut bacteria to lower cholesterol?
Researchers suggest the Ruminococcus gnavus and isoCDCA pathway may become a target for preventing or treating high cholesterol. However, treatments are likely years away, since human trials are needed to confirm safety and effectiveness.
Want to Apply This Research?
- Track your total cholesterol, LDL cholesterol, and triglycerides from each blood test, along with the date and any cholesterol medication you take. If you have a lab report, log the numbers as they appear, and note how often you eat high-fiber foods each week to see possible patterns over time.
- Use the app to set a weekly goal of eating fiber-rich foods such as oats, beans, lentils, fruits, and vegetables on most days. Fiber feeds the beneficial bacteria in your gut and is also part of a heart-healthy diet. Log your servings each day so you can see your progress and adjust your meals.
- Review your cholesterol numbers with your doctor at the intervals they recommend, typically every few months to a year depending on your risk. Over the long term, track trends in your diet, physical activity, and blood test results together. Watch for updates in the research, and bring any new questions about gut health to your healthcare provider rather than making major changes on your own.
This article summarizes early research, much of which was done in mice and laboratory cells, and it does not establish that gut bacteria cause high cholesterol in people. It is not medical advice. Do not start, stop, or change any medication, supplement, or diet based on this information. Talk with your doctor or another qualified healthcare provider about your cholesterol levels and treatment options.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.