If you needed another reason to limit your intake of red meat and energy drinks, here’s one more: Both contain a certain amino acid that leads indirectly to the formation of plaque in the arteries, which could speed the onset of heart disease.

In a study published Sunday in the journal Nature Medicine, Cleveland Clinic researchers found that meat eaters had certain bacteria in their gut that digest the amino acid l-carnitine and spew out a toxic byproduct—called TMAO—that clogs arteries, raising the risk of heart disease. Vegetarians, on the other hand, didn’t produce this byproduct after eating red meat for the study, likely because their digestive system didn’t harbor the bacteria.

The researchers also looked at 10,000 patients who were getting cardiac evaluations at the Cleveland Clinic and found that those with the highest l-carnitine levels in their blood also had the greatest risk of having a heart attack or stroke or of dying from heart disease during the three year study.

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It’s impossible to know at this point how much of the ill health effects of consuming too much red meat come from TMAO and how much comes from red meat’s high content of saturated fat and cholesterol. Studies in mice indicate that TMAO does its damage by triggering the accumulation of cholesterol on artery walls, but that hasn’t yet been demonstrated in humans.

Still, enough evidence has accumulated for the author of the new study to be convinced of TMAO’s dangers. Stanley Hazen, a Cleveland Clinic cardiologist, told the New York Times that he recently reduced his consumption of red meat from several times a week to once every two weeks—eating no more than 4 to 6 ounces at a time.

And he expressed concern about energy drinks that contain carnitine. It’s added to energy drinks and sold as an individual supplement such as this one from GNC because it’s puported to increase energy, build muscle, and burn fat. Instead, it may be speeding the onset of atherosclerosis.

Your safest bet: avoid any sort of drinks or supplements with the amino acid carnitine listed on the label and, yes, reduce your intake of red meat to no more than once a week.