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TMAO (trimethylamine N-oxide) is produced by gut bacteria from choline, lecithin, and L-carnitine-rich foods (mainly fish, meat, egg, and dairy). High levels are associated with heart disease, hardening of the arteries, diabetes, and colon cancer. However, the role of TMAO in these diseases is still controversial. Read more to find out how TMAO levels may affect your health and what you can do to reduce them.

What Is TMAO?

TMAO (trimethylamine N-oxide) is an organic compound produced from TMA (trimethylamine), a common product of plant and animal decomposition [R].

TMA is generated by gut bacteria when they metabolize choline, lecithin (phosphatidylcholine), and L-carnitine [R, R].

TMA is then transferred via the bloodstream to the liver where it becomes oxidized into TMAO, primarily by the enzyme FMO3 [R].

Potential foods that increase TMAO are those rich in choline, lecithin, and L-carnitine, like red meat, eggs, dairy, and saltwater fish [R].

TMAO Blood Test

You can check your TMAO levels with a blood test. However, the test is relatively new and the referent values are still being established.

In a study with 349 healthy subjects, the median value was 3.45 μM. Many had levels close to this value (2.25-5.79 μM). However, values as low as 0.73 μM and as high as 126 μM were also recorded [R].

TMAO levels tend to increase with age [R].

Why Is High TMAO Bad?

1) High TMAO Increases Heart Disease Risk

In a meta-analysis of 19 studies with 19,256 subjects, high TMAO levels were associated with an increased risk of heart diseases, such as heart failure and stroke. Furthermore, people with high levels of TMAO sources, like L-carnitine and choline, were 1.4 times more likely to suffer from heart failure, stroke, or other heart diseases [R].

In another meta-analysis of 11 studies with 7716 subjects, those with elevated levels of this compound had a 23% higher risk of heart diseases and a 55% higher risk of dying (from all causes) [R].

According to a study of 80,978 women and 39,434 men, higher intake of dietary phosphatidylcholine (source of TMAO) resulted in a higher all-cause death risk, especially among diabetics [R].

High TMAO levels increased the risk of blood clots, heart attack, and stroke in over 4,000 subjects [R].

Similarly, high levels of this compound were associated with increased mortality in 720 patients with heart failure [R].

In rats, TMAO increases with age and causes oxidative stress and inflammation in blood vessels, leading to endothelial (blood vessel lining) dysfunction, which increases the risk of heart disease [R].

2) High TMAO May Cause Hardening of the Arteries

High levels of TMAO were associated with increased cIMT (carotid intima-media thickness), an early marker for hardening of the arteries (atherosclerosis), in 220 patients irrespective of other factors, such as insulin resistance, obesity, and fatty liver [R].

Elevated levels of this compound were also associated with higher risk of hardening of the arteries in 220 subjects with chronic kidney disease [R].

Dietary TMAO, L-carnitine, and choline increased the hardening of the arteries in atherosclerosis-prone mice. The effect was blocked by antibiotics, which decreased the activity of gut bacteria [R, R].

3) High TMAO Is Associated with Diabetes

In 2,977 participants, high TMAO levels were associated with an increased risk of type 2 diabetes [R, R].

Of 191 heart disease patients, those with high TMAO were more likely to have diabetes [R].

Dietary TMAO decreased glucose tolerance, increased insulin levels and insulin resistance (HOMA-IR), and increased inflammation in mice on a high-fat diet [R].

All of these increase the risk of developing diabetes.

4) High TMAO Impairs Kidney Function

Chronic kidney disease patients had higher TMAO levels compared to controls (521 patients and 3,166  controls). Furthermore, higher TMAO in chronic kidney disease patients was associated with a 2.8-fold increase in mortality risk [R].

In 179 chronic kidney disease patients, high TMAO was associated with faulty kidney function, chronic inflammation (high IL-6 and CRP), and increased mortality. After kidney transplantation, TMAO levels decreased back to normal [R].

High levels of this compound were also associated with worse kidney function and advanced chronic kidney disease in 227 patients with heart disease [R].

In animals, high dietary TMAO or choline levels caused kidney damage and dysfunction [R].

In another study, high TMAO levels, caused by a high-fat diet, increased oxidative stress and inflammation in the kidneys and lead to kidney damage and dysfunction in mice [R].

5) High TMAO Increases Inflammation

High TMAO levels were associated with higher levels of TNF-alpha, an inflammatory cytokine, but not with IL-6 or CRP in 271 adults [R].

However, high TMAO was associated with chronic inflammation and high IL-6 and CRP levels in 179 patients with kidney disease [R].

This compound increased inflammation by increasing NF-κB (a master-regulator of inflammation) in mice [R].

It also increased inflammation and oxidative stress in human blood vessel cells [R].

6) High TMAO Increases the Risk of Cancer

TMAO contributes to the production of N-Nitroso compounds (NOCs). These products can cause DNA-damage and potentially cancer [R, R].

In 1,670 women, there was a link between higher TMAO and colon cancer. Women with the highest levels of choline, the source of TMAO, were at a 2.4-times greater risk of developing the disease [R].

In 138 subjects, those who had colon cancer had higher TMAO levels. Elevated TMAO levels also predicted lower disease-free survival among colon cancer patients [R].

However, in another study, only elevated choline but not TMAO was associated with increased risk of colon cancer in 1,288 men [R].

TMAO was associated with elevated risk of aggressive prostate cancer in 200 prostate cancer patients [R].

7) High TMAO Causes Liver Dysfunction

In 1,628 adults, high TMAO levels were associated with more severe liver damage and non-alcoholic fatty liver disease [R].

In addition, high levels were associated with worse outcomes in patients with primary sclerosing cholangitis, an immune-related disease of the liver [R].

A high conversion rate of choline into methylamines, such as TMAO, decreases choline levels and causes fatty liver disease in mice [R].

Also, dietary TMAO causes liver damage in mice [R].

8) TMAO May Cause Obesity

Higher FMO3 enzyme activity, responsible for producing TMAO, was associated with higher body mass index (BMI), waist-to-hip ratio, more body fat, and lower insulin sensitivity in 770 men [R].

Blocking FMO3 activity protects mice from becoming obese [R].

These Increase TMAO Levels

1) Animal Products

Eggs, red meat, dairy products, and fish are rich in choline, carnitine, and lecithin, which then get converted to TMAO by gut bacteria [R].

In 297 subjects, fish and meat consumption increased blood TMAO levels [R].

In 40 healthy young men, fish consumption increased TMAO levels more than beef or eggs [R].

Fish protein increased TMAO in mice more than other protein sources such as soy or casein [R].

In rats, beef diet increased TMAO levels more than chicken [R].

Eggs, and especially egg yolks, are rich in choline. Eating more than two eggs per day increased TMAO levels in six healthy volunteers [R, R].

However, another study showed that the intake of up to three eggs per day did not increase TMAO levels, but had beneficial effects such as increasing HDL-cholesterol and choline [R].

Dairy consumption was associated with higher TMAO levels in 271 adults [R].

On the contrary, in 38 overweight or obese women, increased consumption of dairy resulted in lower TMAO levels [R].

Should you stay away from fish and animal products because these can increase TMAO? The answer is not simple.

Many studies show that consuming fish lowers the risk of heart disease. Fish is also an excellent source of omega-3 fatty acids [R, R].

It seems that the benefits of other healthy ingredients found in fish outweigh the effect of higher TMAO, at least when it comes to heart disease prevention.

Diets rich in choline or carnitine also have beneficial effects on human health. These foods are important sources of nutrients, such as iron and vitamin B12 [R].

Therefore, you should take the studies above with a grain of salt.

2) High-Fat Diet

A short-term high-fat diet increased TMAO levels during or after meals but did not have long-term effects in 10 non-obese men [R].

3) L-Carnitine Supplements

Oral L-carnitine supplements increased TMAO levels in 31 patients on hemodialysis [R].

L-carnitine supplements can also increase TMAO levels in people with organic acidemias (these are rare inherited inborn errors of metabolism), irrespective of the meat consumption [R].

4) Gastric Bypass Surgery

In 34 obese people, TMAO levels increased after a gastric bypass surgery, likely due to alterations in gut microbiota [R].

However, gastric bypass surgery decreases overall heart disease risk, so the impact of high TMAO in these cases is still not understood [R].

5) Pollutants

In mice, dioxin-like pollutants, which are highly toxic environmental pollutants, increased the FMO3 enzyme production, which elevated TMAO levels [R].

6) Sleep Deprivation

Sleep deprivation increased TMAO levels in 15 healthy men [R].

7) Pregnancy

Sex hormones during pregnancy increase FMO3 enzyme activity, which can increase TMAO [R].

These Decrease TMAO levels

1) Vegetarian/Vegan/Mediterranean Diet

Among 74 subjects given L-carnitine, meat eaters had greater increases in TMAO levels compared to vegans or vegetarians. This means that vegans and vegetarians have gut bacteria that produce less TMAO [R].

Among 153 people, vegetarians, vegans, and those who adhered to a Mediterranean diet (rich in fruit, legumes, and vegetables) had lower TMAO levels [R].

2) Prebiotics and Potential Probiotics

Probiotics are bacteria that, when digested, have beneficial effects. Prebiotics are plant fibers, which act as fertilizers for the growth of the good bacteria in the gut.

Soluble dietary fiber, acting as a prebiotic, reduced TMAO by over 60% in mice fed red meat [R].

In another study, a single type of prebiotics increased, whereas a prebiotic mixture decreased TMAO levels [R].

This suggests that having a high diversity of gut bacteria is important for controlling TMAO levels.

In human studies, conventional probiotics were unsuccessful in decreasing TMAO [R, R].

However, the bacterium Enterobacter aerogenes, given as a probiotic, decreased TMAO levels in mice [R].

3) Vitamins D and B

In 52 adults, supplementation with vitamins B and D decreased TMAO levels [R].

4) Resveratrol

Resveratrol, found in berries and grapes, decreased blood TMAO levels in atherosclerosis-prone mice [R].

5) Pistachios

A pistachio-supplemented diet decreased TMAO levels in 39 prediabetic subjects [R].

6) Brussels Sprouts

Daily consumption of Brussels sprouts decreased FMO3 enzyme activity in 10 healthy volunteers. This can result in lower TMAO levels [R].

7) DMB Can Decrease TMAO Levels

DMB (3,3-dimethyl-1-butanol) is found in red wine, balsamic vinegar, cold-pressed extra virgin olive oil, and grapeseed oil [R].

It decreases TMAO levels in mice fed high-choline or high-carnitine diets [R].

8) Meldonium

Meldonium is an anti-ischemic medication that increases blood flow and oxygen supply to the body.

This drug decreased blood TMAO levels in eight healthy adults on TMA-rich diets by increasing the elimination of TMAO through urine [R].

In rats, meldonium reduces the production of TMA from L-carnitine and, thus, decreases TMAO levels. Twenty-four hours after meldonium treatment, the TMAO levels in urine were 3.6 times lower [R].

Genes Related to TMAO Levels


FMO3 is a liver enzyme that transforms TMA into TMAO. People with mutations in FMO3 cannot convert TMA to TMAO. They accumulate TMA, which has a specific odor, and develop fish-odor syndrome (trimethylaminuria) [R].

FDA Compliance

The information on this website has not been evaluated by the Food & Drug Administration or any other medical body. We do not aim to diagnose, treat, cure or prevent any illness or disease. Information is shared for educational purposes only. You must consult your doctor before acting on any content on this website, especially if you are pregnant, nursing, taking medication, or have a medical condition.


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  • Elizabeth Swope

    Hello Joe, I refer to your site all the time because of the excellent information, but I would like to unsubscribe to the automatic comments. I don’t see a place to unsubscribe. How would one do that.
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      When you get a new comment, at the bottom of the window there is a link that says “unsubscribe from all follow-up comments.” Hope this helps! If not, please send us an email to support(at)selfhacked(dot)com

  • Colin

    Stop sending messages in this manner. Its intrusive and i dont like the way you just barge in unenvited with no unsubscribe contact. Your messages come in with no email… nothing… please go away.

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      Click on the lock on the left hand side of the URL in your browser and then under Notifications, click Block.

  • Mary Do

    It seemed that the results of these studies somewhat contradicts one another…It is not a clear simple answer that we should not eat those foods/ supplements those were claimed to increase TMA, because to me, once again, science is looking at a single compound without looking at the big picture where there are complec interractiond between various compounds including this TMA, plus many other factors those are also influencing the body conditions. In my personal opinion, this is another piece of the puzzle, but we need the whole picture!

    1. Biljana N

      Exactly, this is a review of what we know at this point about TMAO (through scientific research). But there is a lot of ground left to cover here. There are those who stress the importance of TMAO as THE answer to why we have heart disease, and those who say this is all rubbish. The truth is most likely somewhere in-between. Hopefully, more meaningful studies will soon follow.

  • Eli

    So a tablespoon of sunflower lecithin a day in my smoothies to help with heart and cholesterol, brain health, liver health, blood pressure isn’t advised?



  • Rob White

    I supplement with a tablespoon of non defatted dessicated beef liver powder most mornings. Is this likely to raise TMAO?

  • Rob White

    V interesting how fish is a big contributor to high TMAO.

    One way to get the benefits of DHA /EPA without consuming fish could be to replace it with high omega 3 poultry that is now available in many supermarkets.

  • Mats

    Hello! Thank you for this favourite site! Im in every day. 🙂
    May i ask, do you advice me to stop taking choline, lecithin, and L-carnitine as supplements? Im eating them as suplements.

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