Our bodies are filled with bacteria, with the majority of them living in our guts, outnumbering our own cells 10 to one. For the most part, these bacteria live in harmony with our bodies, eating what we eat, and regulating our metabolism and energy. But when they’re not living in peace, they may be causing disease, as one new Cleveland Clinic study found; a byproduct of their digestion may influence a person’s heart health.

The byproduct, trimethylamine N-oxide, or TMAO, is produced when gut bacteria digest the amino acid carnitine, which is commonly found in animal food products like beef, fish, chicken, milk, and cheese. The body already produces carnitine, and stores it in almost every cell in the body, where it’s used to produce energy. Because of this, it’s not really necessary to get more. The new study found that once gut bacteria produced TMAO, it traveled to the bloodstream where it clogged arteries, leading to heart failure and overall worse outcomes.

“I am excited that these studies suggest TMAO testing may not only help identify those patients at greatest risk, and for whom more aggressive monitoring is needed, but also that TMAO testing may help to tailor dietary efforts to the individual in the hopes of reducing future risks among those high-risk subjects,” said Dr. W.H. Wilson Tang, of the Department of Cardiovascular Medicine at the Miller Family Heart and Vascular Institute, in a press release.

For the study, the researchers followed 720 heart failure patients over the course of five years. They found that there were lower mortality rates when there were high levels of natriuretic peptides, a compound indicative of heart failure, and low levels of TMAO, when compared to patients who had high levels of both. The findings, that TMAO contributed to heart failure and death, were further supported when they found that high levels of TMAO and BNP — another peptide indicative of heart failure — increased risk of death by 50 percent.

Tang’s study builds on a study from 2013, in which he found that TMAO also contributed to a person’s risk of heart disease and stroke, even if a person has no history of either. Though the researchers aren’t suggesting we all stop eating meat, their findings support previous claims that red meat consumption should be limited — and they have good reason to suggest that. “A diet high in carnitine shifts our gut ‘biology’ so meat eaters actually generate more TMAO and compound their risk of cardiovascular disease,” Cleveland Clinic’s website says.

Heart failure is very common, affecting 5.1 million people in the U.S., according to the National Heart, Lung, and Blood Institute. It develops over time and causes the heart to weaken, making it harder for blood to flow to some parts of the body. In turn, a person’s extremities can swell, they can have trouble breathing, or feel tired.

Source: Tang WH, Hazen S, et al. Journal of the American College of Cardiology. 2014.