A substance called TMAO, produced by gut bacteria when you eat certain foods, increases atrial fibrillation risk by 70% according to a 2026 study of 5,090 patients. Gram Research analysis shows that people with higher TMAO levels had significantly more irregular heartbeats, and blocking TMAO production in mice prevented heart rhythm problems even when they ate foods that normally trigger it. The mechanism involves disruption of nerve signals that control heart rate.
Researchers discovered that a substance called TMAO, which is produced by gut bacteria when we eat certain foods, may increase the risk of atrial fibrillation—a condition where the heart beats irregularly. In a study of over 5,000 people undergoing heart procedures, those with higher TMAO levels were 70% more likely to have atrial fibrillation. The research, published in The Journal of Clinical Investigation, suggests that blocking the production of TMAO could potentially prevent this dangerous heart rhythm problem. According to Gram Research analysis, this finding opens a new way to think about preventing heart disease by managing what our gut bacteria produce.
Key Statistics
A 2026 study of 5,090 patients published in The Journal of Clinical Investigation found that people with the highest TMAO levels had a 70% increased risk of atrial fibrillation compared to those with the lowest levels, independent of other heart disease risk factors.
In laboratory mice, dietary choline supplementation significantly accelerated atrial fibrillation onset in mice genetically prone to the condition, while a drug blocking TMAO production reduced this acceleration by more than 50%.
Mice fed a high-TMAO diet showed reduced electrical conduction velocity in heart tissue and enlarged left atria, both physical changes that promote irregular heartbeats.
A TMAO-blocking drug reduced circulating TMAO levels by more than 99% in mice and prevented choline-induced atrial fibrillation development in multiple mouse models.
The Quick Take
- What they studied: Whether a gut bacteria byproduct called TMAO increases the risk of atrial fibrillation, a condition where the heart beats irregularly
- Who participated: 5,090 people who were having heart catheterization procedures (a test where doctors look at heart blood vessels), plus laboratory mice with different genetic backgrounds
- Key finding: People with higher TMAO levels had a 70% increased risk of atrial fibrillation (odds ratio 1.7). When mice were fed extra choline (which the gut converts to TMAO), they developed irregular heartbeats much faster than control mice
- What it means for you: If confirmed in future studies, reducing TMAO levels through diet changes or medications might help prevent atrial fibrillation. However, this research is still early-stage and shouldn’t replace current medical treatments. Talk to your doctor before making dietary changes based on this finding
The Research Details
This research combined two approaches: first, scientists measured TMAO levels in blood samples from 5,090 real patients undergoing heart procedures and tracked whether they had atrial fibrillation. Second, they conducted controlled experiments in laboratory mice to understand how TMAO actually causes heart rhythm problems.
In the mouse studies, researchers fed some mice extra choline (a nutrient found in eggs and meat that gut bacteria convert to TMAO) and others a normal diet. They also tested a drug called iodomethylcholine that blocks the bacterial enzyme responsible for making TMAO. They used electrical pacing studies to see how easily they could trigger irregular heartbeats in the mice.
The researchers also examined the genetic changes in gut bacteria and looked at heart tissue under a microscope to understand the physical changes happening in the heart.
This study design is strong because it combines real-world patient data with controlled laboratory experiments. This two-pronged approach helps prove that TMAO actually causes the problem, not just that it’s associated with it. The mouse experiments show the biological mechanism—how TMAO interferes with nerve signals that control heart rhythm—which makes the human findings more believable
Strengths: Large sample size (5,090 patients), published in a top-tier medical journal, multiple types of evidence (human data plus animal models), researchers adjusted for other heart disease risk factors. Limitations: The human study is observational (not a controlled experiment), so we can’t be 100% certain TMAO causes the problem. Mouse studies don’t always translate perfectly to humans. The study doesn’t tell us how much dietary change would be needed to reduce TMAO levels in real people
What the Results Show
In the 5,090 patients studied, those with the highest TMAO levels were 70% more likely to have atrial fibrillation compared to those with the lowest levels, even after accounting for other risk factors like age, diabetes, and high blood pressure. This association was statistically significant, meaning it’s very unlikely to be due to chance.
In mouse experiments, the results were even more dramatic. Mice fed a diet high in choline (which gets converted to TMAO by gut bacteria) developed atrial fibrillation much faster than control mice. When researchers gave mice a drug that blocks TMAO production, the mice were protected from developing irregular heartbeats, even when fed the high-choline diet.
The mechanism appears to work through nerve signals: TMAO interferes with muscarinic receptors (special proteins that help control heart rhythm through the nervous system). This disruption throws off the balance of the autonomic nervous system—the part of your nervous system that automatically controls heart rate and rhythm without you thinking about it.
Mice on high-choline diets also showed physical changes in their hearts: the left atrium (upper chamber) became enlarged, and the electrical signals traveled more slowly through the heart tissue, both of which promote irregular heartbeats.
Genetic analysis of gut bacteria showed that choline supplementation changed the types of bacteria in the gut—specifically increasing bacteria that produce TMAO. When mice were given the TMAO-blocking drug, many of these bacterial changes were reversed. This suggests that controlling TMAO production could reshape the gut microbiome in beneficial ways. The study also found that the electrical properties of heart cells changed with high TMAO levels, including faster repolarization (the time it takes for heart cells to reset after beating), which can trigger irregular rhythms
Previous research has shown that TMAO is linked to heart disease and stroke, but its role in atrial fibrillation was unclear. This study is the first to demonstrate a direct connection between TMAO and atrial fibrillation risk and to identify the specific mechanism (interference with nerve signals controlling heart rhythm). The findings build on earlier work showing that gut bacteria influence heart health, but go deeper by identifying TMAO as a specific culprit and showing that blocking it can prevent problems
The human study observed associations but didn’t prove cause-and-effect (people with high TMAO might differ in other unmeasured ways). Mouse studies don’t always translate to humans—mice have different genetics and lifespans. The research doesn’t tell us how much choline intake is safe or unsafe for humans. The study focused on people undergoing cardiac catheterization, who may have different baseline heart health than the general population. Long-term human studies would be needed to confirm that reducing TMAO actually prevents atrial fibrillation in real patients
The Bottom Line
Current evidence (moderate confidence): If you have risk factors for atrial fibrillation or a family history of it, discuss with your cardiologist whether limiting high-choline foods (eggs, red meat, organ meats, dairy) might be beneficial. However, don’t eliminate these nutritious foods without medical guidance. Future recommendation (low confidence, pending human trials): Medications that block TMAO production may become a preventive treatment, but these are not yet available for this purpose. Continue following standard atrial fibrillation prevention advice: manage blood pressure, maintain healthy weight, limit alcohol, and exercise regularly
Most relevant for: People with a family history of atrial fibrillation, those with high blood pressure or heart disease, people over 65. Less immediately relevant for: Young, healthy people with no heart disease risk factors. Important note: This research should not replace current medical treatment for atrial fibrillation. If you have atrial fibrillation, continue taking prescribed medications and follow your doctor’s advice
If dietary changes were to help, benefits would likely take weeks to months to appear, since it takes time for gut bacteria populations to change and for TMAO levels to decrease. Any medication-based approach would need to be tested in human clinical trials first, which typically takes 3-5 years. Don’t expect immediate results from any intervention
Frequently Asked Questions
What foods increase TMAO levels in your body?
Foods high in choline—including eggs, red meat, organ meats, full-fat dairy products, and some nuts—are converted by gut bacteria into TMAO. Fish and poultry contain choline but appear less likely to increase TMAO. Individual responses vary based on gut bacteria composition
Can you lower TMAO levels through diet?
Research suggests reducing choline-rich foods may lower TMAO, though human studies confirming this are limited. A 2026 study showed that blocking the bacterial enzyme that produces TMAO reduced levels by over 99%, but this drug isn’t yet available for patients. Dietary changes should be discussed with your doctor
Does everyone with high TMAO develop atrial fibrillation?
No. The 2026 study showed a 70% increased risk, meaning high TMAO increases likelihood but doesn’t guarantee atrial fibrillation will develop. Other factors like genetics, age, blood pressure, and existing heart disease also play major roles in determining who develops irregular heartbeats
Is it safe to eliminate choline-rich foods from your diet?
Choline is an essential nutrient needed for brain health and cell function, so complete elimination isn’t recommended. Instead, moderate consumption of choline-rich foods while emphasizing fish, poultry, and plant-based proteins may be a balanced approach. Consult your doctor before making major dietary changes
When will TMAO-blocking medications be available for atrial fibrillation prevention?
The TMAO-blocking drug tested in mice (iodomethylcholine) is not yet approved for human use. Clinical trials in humans would need to occur first, typically taking 3-5 years. Current atrial fibrillation prevention relies on managing blood pressure, weight, and other established risk factors
Want to Apply This Research?
- Track daily choline intake (eggs, red meat, dairy, nuts) and correlate with heart rate variability measurements if your device supports it. Log any episodes of heart palpitations or irregular heartbeats alongside dietary patterns to identify personal triggers
- Set a weekly goal to reduce high-choline foods by 20-30% and replace them with choline-free alternatives (chicken, fish, vegetables, grains). Use the app to log meals and receive notifications when choline-rich foods are selected, with suggestions for lower-choline swaps
- Monthly check-ins comparing heart rhythm stability (palpitations, irregular beats) to choline intake patterns. If using a wearable device, track resting heart rate and heart rate variability trends over 3-month periods to assess whether dietary changes correlate with improved heart rhythm stability
This research is preliminary and should not replace professional medical advice. The findings are from laboratory studies and observational human data; they have not yet been confirmed in randomized controlled trials testing dietary or medication interventions in humans. If you have atrial fibrillation or are at risk for it, consult your cardiologist before making dietary changes or considering any new treatments. Do not stop taking prescribed heart medications based on this information. This article is for educational purposes and is not medical advice.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.