Gut reaction: How bacteria in your belly may affect your heart

You know the old saying, the way to a man's heart is through his stomach? It turns out there's a whole new twist to that cliché. (And just to be clear, it applies women, too).

You're probably well aware that what you eat plays a role in your heart's health. Now, scientists are learning more about how the trillions of bacteria dwelling deep inside your digestive tract can affect your risk of cardiovascular disease.

Collectively known as the gut microbiota, these microbes assist with digestion, but also make certain vitamins, break down toxins, and train your immune system. Over the past decade, scientists have uncovered compelling connections between different types of gut microbes and the development of obesity and diabetes — two factors closely tied to a higher risk of heart disease. Recently, several studies have explored how our gut microbes interact with the food we eat to spur artery-damaging inflammation and narrowing. These findings are still preliminary, but experts hope they'll one day lead to personalized diet recommendations or other therapies to lower the risk of heart disease.

Artery damage

The initial discovery connecting the gut microbiota to cardiovascular disease came from researchers at the Cleveland Clinic. They discovered that when gut microbes feed on a chemical called choline (found in eggs, red meat, and dairy products), they produce a compound called TMA. In the liver, TMA is converted to TMAO, which causes hardening of the arteries (atherosclerosis) in mice and is linked to a higher risk of heart disease in humans.

"For the first time, they showed how the relationship between a dietary component, bacterial metabolism, and human metabolism can have adverse consequences for blood vessels," says cardiologist Dr. Joseph Loscalzo, who chairs the department of medicine at Harvard-affiliated Brigham and Women's Hospital.

Avoiding blockages

The investigators then tested a molecule that blocks the production of TMA, which they gave to mice prone to atherosclerosis, thanks to their genes and a high-fat diet. The molecule, called DMB, occurs naturally in olive oil and red wine. The mice that got DMB in their water had healthier, clearer arteries than those that didn't.

Earlier this year, Chinese researchers described a different but related approach to preventing blood vessel injury in atherosclerosis-prone mice. They found that by giving the mice a specific strain of bacteria called Akkermansia muciniphila, they could prevent inflammation — the chronic, persistent immune response that contributes to the buildup of fatty plaque in arteries. The effect was largely due to a protein that was able to "tighten up" the communication between cells in the inner lining of the gut, Dr. Loscalzo explains. As a result, fewer toxins from the diet could pass from the gut into the bloodstream, which in turn dampened inflammation.

Gut check?

Together, these findings suggest that altering the gut microbiota in different ways might minimize blood vessel damage, says Dr. Loscalzo. There's also some evidence that the gut microbiota may influence the levels of cholesterol and other fats in the bloodstream, as well as blood pressure.

But for now, it's far too early to offer any specific advice based on this research. The human microbiome is unique, which makes it hard to define exactly what constitutes a healthy gut environment. However, a more diverse mix of bacteria seems to be healthier than a limited one. People who eat a traditional, plant-based Mediterranean or Asian diet tend to have a greater diversity of intestinal bacteria than Americans and Europeans, whose diets are heavier in red meat, sugars, and other refined carbohydrates, and lighter in fruits and vegetables.