How Gut Bacteria From Your Diet Affect Heart Disease Risk

Research-informed explainer — last updated April 12, 2026

The bacteria living in your gut do far more than help digest food. When you eat red meat, eggs, or dairy, specific gut bacteria metabolize the nutrients in those foods and produce a compound called TMAO that gets absorbed into your bloodstream and promotes the buildup of artery-clogging plaque. This gut-heart connection — discovered through research at the Cleveland Clinic and confirmed in multiple large studies — offers a new way to think about why diet matters for heart disease, and raises the possibility of measuring and modifying your personal cardiovascular risk through your microbiome.

This explainer draws on peer-reviewed research from cardiologists and gastroenterologists listed in the Convene directory. Their published work includes the foundational 2011 Nature paper establishing the gut-cardiovascular link (5,444 citations), the 2013 New England Journal of Medicine study on phosphatidylcholine and cardiovascular risk, the l-carnitine and atherosclerosis paper in Nature Medicine, and research on gut microbiome inhibition as a potential therapy.

What this finding is

The discovery started with a question: why does eating red meat raise cardiovascular risk even accounting for its saturated fat and calorie content? Cleveland Clinic researchers led by Stanley Hazen and Wai Hong Tang found the answer in an unexpected place — the gut microbiome.

When you eat foods rich in phosphatidylcholine (a fat found in red meat, eggs, dairy, and fish), your gut bacteria convert choline into trimethylamine (TMA). Your liver then processes TMA into trimethylamine N-oxide (TMAO). TMAO circulates in your blood and, at elevated levels, accelerates atherosclerosis — the plaque accumulation in arteries that underlies most heart attacks and strokes.

The gut-TMAO-heart axis was described in a landmark 2011 Nature paper [1] and extended in a 2013 New England Journal of Medicine study that measured TMAO levels in 4,007 patients and showed that higher TMAO levels were independently associated with a greater risk of major cardiovascular events — heart attack, stroke, or death — over three years [2]. This was not a mouse study or a lab observation. It was a prospective human study showing that a gut-derived metabolite predicted cardiovascular outcomes.

How the mechanism works

Here is the specific pathway, step by step:

1. You eat a steak, eggs, or cheese — all high in choline, phosphatidylcholine, or l-carnitine.
2. Bacteria in your gut (particularly species in the genera Firmicutes and Proteobacteria) contain enzymes that convert choline and l-carnitine into TMA.
3. TMA is absorbed through the gut wall into portal circulation and delivered to the liver.
4. The liver enzyme FMO3 (flavin-containing monooxygenase 3) oxidizes TMA into TMAO.
5. TMAO enters the bloodstream and reaches arterial walls.
6. There, TMAO activates macrophages (immune cells), promotes the uptake of cholesterol into those cells, and accelerates the formation of foam cells — the lipid-laden macrophages that are the building blocks of atherosclerotic plaque [1].

A companion paper published in Nature Medicine in 2013 focused specifically on l-carnitine, a nutrient concentrated in red meat. In both mice and humans, l-carnitine was converted to TMAO by gut bacteria, and the amount of TMAO produced depended on the composition of the individual's gut microbiome [6]. Omnivores who ate red meat regularly produced far more TMAO from a carnitine dose than vegans and vegetarians, whose gut bacteria lacked the microorganisms needed for robust TMA production. This is direct evidence that your gut bacteria profile — shaped over years by your diet — determines how much cardiovascular risk you extract from any given meal.

TMAO and platelet clotting

Beyond plaque formation, research from the Cleveland Clinic published in Cell in 2016 showed that TMAO directly affects platelets — the blood cells that form clots. Higher TMAO levels made platelets more reactive, increasing the tendency to clot in response to normal stimuli. In animal models, TMAO-fed mice formed larger, faster clots when their arteries were injured [3].

This adds a second cardiovascular mechanism: TMAO does not just build plaque over years, it also acutely increases clotting tendency, potentially raising the risk that a plaque will rupture and trigger a heart attack on any given day. Patients with high TMAO levels would, by this model, have both more plaque and a higher likelihood that a plaque rupture turns fatal.

Can you measure your TMAO level?

Yes. TMAO is measurable in a standard blood test. Cleveland Clinic Laboratories and several reference labs offer fasting TMAO measurement. Reference ranges have been established based on the prospective cardiovascular outcome studies. High TMAO levels (generally above the 75th percentile in population studies) are associated with significantly higher cardiovascular event rates.

TMAO measurement is not yet a routine part of standard cardiovascular risk assessment the way cholesterol or blood pressure are. It is more commonly ordered by cardiologists with a specific interest in precision cardiovascular risk stratification, particularly in patients who have cardiovascular disease despite otherwise-favorable traditional risk factors, or in patients with strong family history whose standard labs look normal.

What controls TMAO levels?

TMAO levels are driven by three factors: diet, gut microbiome composition, and liver enzyme activity.

Diet is the most modifiable factor. Reducing intake of choline-rich and l-carnitine-rich foods lowers TMAO. Red meat, eggs, and full-fat dairy are the main sources. Fish also contains choline and, interestingly, some fish contain preformed TMAO directly (particularly deep-sea fish that use TMAO to maintain protein function under pressure). Despite this, fish consumption is not consistently associated with higher cardiovascular risk, possibly because the other components of fish — omega-3 fatty acids, lower saturated fat — offset the TMAO effect.

Gut microbiome composition determines how much TMA is produced. People with a microbiome that is rich in TMA-producing bacteria convert more dietary choline and carnitine into TMA for the same dietary intake. Microbiome composition shifts with diet over weeks to months, antibiotic exposure, and probiotic use, but changes slowly and is not easily controlled.

Genetics plays a role. The liver enzyme FMO3 that converts TMA to TMAO shows genetic variation. People with naturally lower FMO3 activity produce less TMAO from the same amount of dietary choline. A 2013 Cell Metabolism study confirmed that both genetic and dietary factors regulate TMAO levels [5].

Can the gut microbiome be modified to lower TMAO?

This is an active area of research with early but promising results.

Dietary change is the most proven approach. Switching to a plant-based or reduced-meat diet measurably lowers TMAO levels within weeks. Vegans produce substantially less TMAO in response to carnitine loading than omnivores, because they lack the TMA-producing gut bacteria that meat-eating cultivates [6].

A targeted inhibitor was tested in 2015 research from the Hazen laboratory. Rather than killing gut bacteria (with antibiotics, which would cause broad disruption), the team developed a non-lethal inhibitor — called 3,3-dimethyl-1-butanol (DMB) — that specifically blocks TMA lyase, the bacterial enzyme responsible for TMA production. In mice, DMB reduced TMAO levels and significantly reduced atherosclerosis without disrupting the gut microbiome composition. The approach was effective over months of treatment [4]. This inhibitor has not yet been tested in clinical trials in humans, but it established the proof of concept that targeting the gut microbiome pathway pharmacologically is feasible.

Resveratrol (found in red grapes and wine) has been shown to shift gut microbiome composition in a direction that reduces TMAO production in some studies, though the clinical significance is uncertain.

Probiotic supplementation with certain Lactobacillus strains modestly reduces TMAO in preliminary studies. The effect size is smaller than dietary change.

How gut dysbiosis connects to metabolic risk more broadly

The gut microbiome influences heart disease risk through pathways beyond TMAO. Research from Yale connecting gut dysbiosis to NAFLD (non-alcoholic fatty liver disease) — a condition tightly linked to cardiovascular risk — found that inflammasome-mediated disruption of the gut microbiome accelerates liver fat accumulation and metabolic inflammation [7]. This broader gut-metabolic-cardiovascular axis means that maintaining a healthy microbiome through a diverse, plant-rich diet may reduce cardiovascular risk through multiple parallel mechanisms simultaneously.

Questions to ask your cardiologist

• Is TMAO measurement appropriate for me given my cardiovascular risk profile?
• If my TMAO level is elevated, what dietary changes would most effectively lower it?
• Should I reduce my intake of red meat and eggs beyond what general guidelines already recommend, based on my specific risk factors?
• Are there any clinical trials for microbiome-targeted cardiovascular therapies that I might be eligible for?
• How much of my cardiovascular risk might be explained by gut microbiome factors versus genetics, cholesterol, and blood pressure?

The bottom line

The discovery that gut bacteria convert nutrients from red meat and eggs into a compound that accelerates artery plaque is one of the most concrete mechanistic explanations for the diet-heart connection ever established. TMAO is measurable, its cardiovascular effects have been confirmed in large prospective human studies, and the pathway from diet to gut bacteria to TMAO to plaque has been traced step by step. This does not mean a single steak will damage your arteries — it means that a diet consistently high in red meat and choline-rich foods cultivates gut bacteria that steadily produce TMAO, and that this process contributes meaningfully to lifetime cardiovascular risk. Reducing red meat intake remains one of the most evidence-backed dietary changes you can make for your heart, and the TMAO mechanism explains part of the reason why.