The Link between Diet, the Gut Microbiome, & Heart Disease

The Link between Diet, the Gut Microbiome, & Heart Disease


Bacteria and other critters in our gut microbiome play a very important role in our health (for more info read our blog article on the microbiome), but did you know that they can also contribute to disease?

Certain species of bacteria produce byproducts during digestion called TMAO that may lead to heart disease and stroke. This should be concerning since heart disease is one of the leading causes of death and morbidity (ill health) worldwide. To advocate for our health and wellbeing, we need to educate ourselves on topics such as TMAO.

We introduced TMAO in our last blog on choline. If you haven’t already read this don’t worry. We are going to catch you up with more details on what TMAO is and how we can protect ourselves from its effects on our health.

What is TMAO?

Picture this—you sit down to eat fancy steak dinner complete with shrimp and scallops (this clearly wouldn’t be the case for all you vegans out there!). Your gut bacteria begin feasting on the choline and carnitine found in this meal and produce a byproduct called TMA (trimethylamine). Your liver takes that TMA and converts it into TMAO (trimethylamineN- oxide).

Choline is found in foods such as meat, eggs, poultry, fish, shellfish, dairy foods, and to a lesser extent in plant foods such as cruciferous vegetables and beans.

Carnitine is found in foods such as meat, eggs, poultry, fish, shellfish, and dairy. In general, the redder the meat, the more carnitine it contains.

*Animal products are the best sources of both choline and carnitine*

What effect does TMAO have on health?

TMAO becomes an issue when high levels build up in the body. There is growing evidence from research studies that support a strong association between high levels of TMAO and increased risk of developing heart disease. According to a news article published in JAMA, three recent (2019) analyses showed that high levels of TMAO were linked with a higher risk for both heart disease and early death from any cause. Other studies showed that:

  • People with higher levels of TMAO may have more than twice the risk of heart disease, stroke, other negative cardiovascular problems compared to those who had lower levels.
  • High TMAO levels were found to be linked to heart failure and kidney disease.
High levels of TMAO may also be linked to:
  • Inflammatory bowel disease (IBS), non-alcoholic fatty liver disease, and the development of diabetes

How Diet Impacts Levels of TMAO

Diet plays a key role in the production of TMAO, since foods that contain choline and carnitine are needed to produce TMA, which ends up being converted into TMAO.

Diet also impacts our gut microbiome. For example, eating meat and other animal products changes the composition of our microbiome— for instance, the more red meat that you eat, the more your body produces meat-eating bacteria in your gut.

The amount of TMAO produced depends on the composition of your gut microbiome. For example, only certain species of microbes contain the genes that produce TMA.

What you need to know when it comes to diet, your gut microbiome, & levels of TMAO:

  • Eating a diet high in animal foods, such as the paleo diet, has been shown to double levels of TMAO in the blood. For example, researchers found that participants who were on the paleo diet had higher concentrations of bacteria that produced TMAO.
  • Omnivores have been shown to have much higher levels of TMAO than vegans and vegetarians. This study compared 23 long-term (>1 year) vegans and vegetarians to 51 omnivores. It was found that TMAO levels were significantly lower in both the vegans and vegetarians. Even when given oral carnitine supplements, the vegan and vegetarians had a reduced capacity to produce TMAO. Lastly, analysis of fecal samples showed that omnivores had different gut bacteria compared to the vegans and vegetarians.
  • If a vegan or vegetarian eats red meat, they will not be able to produce TMA, at least at first. However, over time, if they continue to eat red meat, their bodies will develop more and more of the microbes that produce TMA, which will lead to their bodies producing more TMAO.
  • Western-style diets (high-fat) have shown to increase TMAO levels.

Although this is all credible evidence that points towards animal products, especially red meat, as being the culprit for high levels of TMAO, it is important to note that production of TMAO is individualized.

For example, blood levels of TMAO can be determined by diet, liver activity, and kidney function. Genetic factors don’t seem to play much of a role in TMAO levels, which suggests that the interactions between diet and the gut microbiome are likely the main determinants of TMAO levels in healthy individuals.


How to Lower Levels of TMAO

The answer pretty obvious at this point! Adopt more of a plant-based diet and eat less red meat and other animal products.


  • Fiber (found only in plants) has been shown to decrease TMAO. A diet high in fiber encourages the development of microbes that produce short-chain fatty acids (SCFAs). There are many health benefits when it comes to SCFA’s including improved immunity, anti-inflammatory and antimicrobial effects, and may reduce blood pressure (high blood pressure is a risk factor for heart disease).
  • Polyphenols (abundant in plant foods) provide anti-pathogenic and anti-inflammatory effects as well as cardiovascular protection.
  • Resistant starch (found in many plant foods, including whole grains) is vital to the health of our gut microbiome. A lack of resistant starch in the diet may change the population of bacteria in the gut to bacteria that are able to produce higher levels of TMAO.

Plant-based diets do much more than lower levels of TMAO.

Plant-based diets are fantastic for our heath for a variety of reasons, including:

  • Increases strains of beneficial bacteria and leads to a healthier gut microbiome. A plant-based diet has been shown to be beneficial for health by increasing strains of beneficial bacteria and promoting the development of a more diverse and stable microbiome.
  • Prevents & reverses chronic diseases. Research has shown that a plant-based diet is one of the best ways to prevent chronic disease and has been shown to reverse chronic diseases that have already developed.

We don’t have all the answers when it comes to the intricate mechanisms behind TMAO production and gut microbiome, but we do know that high levels of TMAO are strongly associated with heart disease, stroke, and other negative health outcomes. We also know that vegans and vegetarians have significantly lower levels of TMAO compared to omnivores and those who eat diets heavy in animal products, such as the paleo diet.

This shows that what we choose to eat matters big time and will either enhance our health and vitality or end up sabotaging it.


  • “Cleveland Clinic Studies Reveal Role of Red Meat in Gut Bacteria, Heart Disease Development”. Cleveland Clinic, 2018,
  • Harvard Medical School. “Red meat, TMAO, and your heart.” Harvard Health Publishing, 2019,
  • Simó, Carolina, and V. García-Cañas. "Dietary bioactive ingredients to modulate the gut microbiota-derived metabolite TMAO. New opportunities for functional food development." Food & Function (2020).
  • Smits, Loek P., et al. "Effect of vegan fecal microbiota transplantation on carnitine‐and choline‐derived trimethylamine‐N‐oxide production and vascular inflammation in patients with metabolic syndrome." Journal of the American Heart Association 7.7 (2018): e008342.
  • Tomova, Aleksandra, et al. "The effects of vegetarian and vegan diets on gut microbiota." Frontiers in nutrition 6 (2019): 47.

Trish Shea R.D.

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