How does the gut microbiome affect the heart?

The evidence is clear that nutrition is a significant, yet under appreciated component of cardiovascular health. While undoubtably the value of good nutrition lies in the vitamins, minerals, antioxidants, and fiber provided, mounting evidence suggests that the value of a good diet stretches beyond just the value it provides directly to our bodies.

The intestinal microbiome—the trillions of microbial cells that putatively play a role in the development or progression of numerous disease processes— is impacted by our daily dietary habits, and in turn, our risk for cardiovascular disease. Let’s explore.

What is the microbiome?

It’s totally mind boggling, but we are actually mostly non-human. There are trillions of microorganisms - bacteria, viruses, and fungi - living throughout our body, known as the microbiome. The microbiome affects many processes within our body, nowhere more so apparent than in the gut.

What does the gut microbiome do?

Our gut microbiome chomps on partially digested foods in the distal portion of our gut and then churns out biologically active metabolites. It turns out that what we eat can affect the composition of our gut microbiome, as well as which active metabolites get produced. This can influence our health, in both positive and negative ways.

Gut bacteria are involved in nutrient absorption, glucose regulation, energy homeostasis, immune response, and drug metabolism. They produce vitamins, steroid hormones, and neurotransmitters which are important for our bodies. However, they can also produce molecules such as trimethylamine (TMA) that harbor the potential to cause damage.

What is dysbiosis?

Dysbiosis is an alteration in your gut microbiome such that there are less beneficial gut microbes and more disease causing microbes. There is also a loss of microbial diversity in the digestive tract. 

The development of dysbiosis has been associated with increased risk of heart disease, as well as other chronic disease such as autoimmune disease, diabetes, allergies, and obesity. It is thought that dysbiosis is the result of diet as well as medication use, stress, poor sleep, and environmental factors.

How might the gut microbiome affect heart health?

One metabolite made by the gut has been linked to increased risk for heart disease called trimethylamine-N-oxide (TMAO). 

Carnitine (and perhaps choline), found in abundance in animal-based foods such as red meat, liver, and egg yolk, are metabolized by our gut into trimethylamine (TMA). In and of itself TMA hasn’t been found to be an issue, but it undergoes oxidation by liver enzymes to its more nefarious alter ego, trimethylamine-N-oxide (TMAO).

Elevated circulating levels of TMAO appear to independently predict risk for atherosclerosis. In a study that followed 4007 people for 3 years following elective coronary angiography, an elevated TMAO level predicted an increased risk of major adverse cardiovascular events including heart attack, stroke, and death. Other studies have shown that this elevated risk continues to be seen even after controlling for other possible confounders such as cholesterol intake. Furthermore, TMAO blood levels showed a significant, graded association with cardiovascular disease prevalence. Those with sustained higher levels of TMAO over a long period of time appear to have a significantly higher risk of heart disease, independent of other traditional risk factors.

It’s important to point out that while TMAO appears strongly associated to increased risk for cardiovascular disease, it has not been established as causative. Mechanistically, it may promote vascular inflammation and clotting, so it’s quite likely that it’s not just an innocent bystander.

How can the gut microbiome help us?

While it looks like TMAO may be bad news, our gut microbiome may also make things that can reduce our risk of heart disease.

Short-chain fatty acids (SCFAs) are made by fermentation of dietary fiber and resistant starches inherent in plant-based diets in the colon. These metabolites may play a role in modifying systemic blood pressure via modulation of the sympathetic nervous system, inflammatory responses, and insulin sensitivity.

One SCFA in particular, butyrate, appears to be important in maintaining the intestinal gut mucosal barrier - loss of this SCFA is associated with increased inflammation, which we know is implicated in heart disease.

What can I do to optimize my gut microbiome for heart health?

We still have a lot to learn about the gut microbiome and its effect on chronic disease.

We don’t know the “perfect” gut microbial makeup, and it may be very different for each one of us based on our genetics and epigenetic factors (how our genes are expressed and passed down to the next generation).  Some studies have demonstrated large inter-individual variation in gut microbial composition and response. Different microbial pathways may be more or less relevant for each of us. A more recent study, however, found a fairly consistent microbial “signature” linked to optimal cardiometabolic health.

That said, current available evidence suggests that our microbiome responds to our daily choices, particularly when it comes to nutrition.  One study suggests that those with healthy dietary patterns can modify the unfavorable effects of TMAO on heart disease risk.

Some ways we may be able to optimize our gut microbiome:

• Maximize your plant-based diversity aka #eattherainbow. Evidence suggests that individuals with higher plant varieties per week (40 or more) have the most diverse microbiomes. We do not know if this then translates to better heart health outcomes, however there’s more than enough reasons to eat more plants! Also consider fermented foods, which are high in prebiotics and probiotics.

• Avoid or minimize animal products and ultra processed foods. Red meat, in particular, has been associated with high levels of TMAO, and in one study, significant decreases in TMAO were seen in just 4 weeks of red meat elimination. TMAO levels were equivalent in the white meat and non-meat eaters.

• Increase your time in nature & play in the dirt

• Limit unnecessary medications, particularly antibiotics, and supplements. That said, benefits of some medications like metformin may actually be due to how they impact the microbiome (in good ways) so this may not always be the case. As with everything, discuss with your doctor prior to making any changes.

• Decrease stress and prioritize sleep

Within the gut, our daily choices may produce a selection of the fittest microbial species that ultimately determines health outcomes through the production of metabolically active products that have the potential to heal, or to harm, our long-term health. We still have a lot to learn so keep your eye out for the latest science in this field - it will be interesting!