Scientists think they've found a link between the bacteria that lives in everyone's gut and the process of hardening arteries. What does that mean for you and your family?

Diet and Disease Risk

Eating too much red meat has long been associated with increased levels of blood cholesterol, which can contribute to the build-up of plaque (debris made up of substances like cells, fats, and connective tissue) in the arteries. This in turn can cause atherosclerosis (the thickening of artery walls), and lead to heart attack and stroke. But not everyone who eats meat has high cholesterol, and many people with normal blood cholesterol have heart attacks, so the link has never been crystal clear.

But now, research published in the journal Nature Medicine proposes a new link between red meat and heart disease. And it has nothing to do with cholesterol.

Gut Bacteria, Red Meat, and Your Arteries

Trillions of gut bacteria, or gut flora, live in your intestine, where they stay busy helping you digest different foods and absorb the various nutrients provided by these foods. The balance of gut flora—how much of which kind of bacteria resides in the gut—varies from person to person, and depends in part on differences in individual diets.

The TMAO Connection

Red meat contains an amino acid (protein) called L-carnitine, or simply carnitine, which is digested by naturally occurring bacteria that especially thrive in the lower intestines of meat eaters. Once digested, carnitine is ultimately transformed into a substance known as trimethylamine-N-oxide (TMAO). In 2011, researchers found that TMAO may contribute to hardening of the arteries, which can ultimately lead to a heart attack or stroke.

Now, a follow-up study has found that a similar chain of events occurs in the body after digesting lecithin, a nutrient concentrated in egg yolks. Both carnitine and lecithin break down to produce yet another substance, known as choline, which, when acted on by certain intestinal bacteria, produces TMAO.

When compared to people who eat a vegetarian or vegan diet, meat eaters are generally more likely to develop atherosclerosis and have higher levels of blood cholesterol and fats. In the lecithin study, researchers theorized that since vegetarians consume less carnitine, they produce less TMAO. Meat eaters who consume large amounts of carnitine or lecithin produce more TMAO, and may be at higher risk of developing atherosclerosis.  

While it's far from the final word on red meat and heart disease, "This new research offers a possible explanation of the observed benefits of that kind of diet," says New Jersey cardiologist William A. Tansey, MD. A confirmation of the link between specific gut bacteria and atherosclerosis could lead to the development of new ways to diagnose and treat heart disease.

What You Can Do

In the meantime, "The American Heart Association has long recommended a diet that emphasizes lean meat, fish, poultry, fruits, nuts, and vegetables to maximize heart health and minimize the occurrence of heart attack and stroke," says Tansey.

William Tansey, III, MD, FACC, ACP, FAHA, reviewed this article.


Koeth, RA. et al. "Intestinal Microbiota Metabolism of L-carnitine, a Nutrient in Red Meat, Promotes Atherosclerosis." Nature Medicine 2013; 19(5):576-587. Page accessed 10 August 2013.

Wang, Z. et al. "Gut Flora Metabolism of Phosphatidylcholine Promotes Cardiovascular Disease." Nature 7 Apr 2011; (472):57-65. Page accessed 10 August 2013.