The fat and cholesterol found in a steak may not be the only components bad for the heart, according to researchers who have found another substance in red meat that can clog the arteries.

The substance is called carnitine, and as bacteria in the gut break it down, it turns into compound known to harden arteries, according to a study published Sunday in the journal Nature Medicine.

What’s more, people who eat a lot of meat allow more of the bacteria that convert carnitine to the harmful compound to grow, increasing its effect.

Previous research has shown that high levels of meat-eating are linked to cardiovascular risk, due in part to the saturated fats and cholesterol in meat. However, the higher levels of these ingredients aren’t enough to explain the difference in heart disease between meat eaters and vegans or vegetarians.

This study, which takes into account the differences in the stomach’s inhabitants, may begin to explain the difference.

“The bacteria living in our digestive tracts are dictated by our long-term dietary patterns,” said study author Stanley Hazen, the section head of Preventive Cardiology and Rehabilitation at Cleveland Clinic, in a statement. “A diet high in carnitine actually shifts our gut microbe composition to those that like carnitine, making meat eaters even more susceptible.”

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