Healthy gut, healthy heart

The gut is known as the "second brain," as it produces many of the same neurotransmitters, chemicals released by nerves needed for communication with other nerves and tissues. The gut and brain are also connected through a joint partnership called the gut-brain axis that links biochemical signals both to and from the gastrointestinal tract and the central nervous system.

But what about the gut and the heart? Do they have a similar connection?

Research suggests there might be a link, but that it travels in one direction — from the gut to the heart — and that keeping your gut healthy can be another means to protect against heart disease.

The gut-heart connection

The gut is the primary home to trillions of microbes, collectively known as the human microbiota. These microbes help with digestion, manufacture certain nutrients, and release substances that have wide-ranging health effects.

"There's a complex interplay between the microbes in our intestines and most of the systems in our bodies, including the vascular, nervous, endocrine, and immune systems, all of which are linked with cardiovascular health," says Dr. Stanley Shaw, a cardiologist at Brigham and Women's Hospital.

Since diet plays a significant role in the composition of gut microbiota, what you feed your gut can therefore affect heart health — for better and for worse.

One way the gut does this is with metabolites, substances the gut microbiota creates when breaking down food. One particular gut metabolite, trimethylamine (TMA), forms when gut microbes feed on choline, a nutrient found in red meat, fish, poultry, and eggs. In the liver, TMA gets converted to trimethylamine N-oxide (TMAO), a substance strongly connected with forming artery-clogging plaque.

Research has shown that people with high TMAO levels in their blood are more likely to suffer a heart attack or stroke than those with lower levels. Since red meat is a main source of TMA, cutting back can stop the gut from making too much TMAO.

In fact, a study in the September 2022 issue of Arteriosclerosis, Thrombosis, and Vascular Biology found that among nearly 4,000 people ages 65 and older, those who ate an average of 1.1 servings of red meat per day had a 22% higher risk of heart disease compared with those who ate less.

The researchers pointed out that about 10% of this added risk could be attributed to increased levels of TMAO as well as two other metabolites — gamma-butyrobetaine and crotonobetaine — which also are made by gut bacteria from components in red meat.

Fiber at work

Fiber also helps support the gut and thus the heart. According to some estimates, fiber-rich diets can lower the risk of heart disease and stroke by as much as 30%. Fiber in the small intestine binds fat and cholesterol, decreasing absorption and lowering blood cholesterol levels.

But the gut's microbiota also helps out. Fiber gets broken down by bacteria in the colon to form short-chain fatty acids. These compounds interact with specific receptors on cells that regulate blood pressure, better control blood sugar and body weight in people with diabetes, and dampen inflammation — all of which can improve heart health.

Other supporting foods

It's unclear whether eating other foods that improve gut microbiota — for example, probiotics (beneficial bacteria) found in yogurt and fermented foods (sauerkraut, miso, tempeh) — can also support heart health.

The best advice for helping your gut help your heart is to follow a plant-based diet like the Mediterranean diet or similar eating patterns. These involve limiting red meat and eating plenty of fiber-rich fruits, vegetables, and whole grains, all of which can have favorable effects on the gut," says Dr. Shaw. "And if your gut is healthy, there is a greater chance your heart is healthy, too."

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