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Red meat has been under scrutiny for its role as a contributor to poor health and diseases. People who consume red meat in excess have a higher risk for obesity, heart disease, and other health complications, and according to a new study, another health issue was recently linked to red meat once again. The study done by researchers from the Cleveland Clinic found that red meat triggers the growth of a type of bacteria responsible for clogging arteries.

The research team, headed by Stanley Hazen, M.D., Ph.D., and Robert Koeth, a medical student from the Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, studied the levels of carnitine, which is a compound, and trimethylamine-N-oxide (TMAO), which is a metabolite previously linked to atherosclerosis, a condition involving the thickening of artery walls due to fat build up. The researchers knew that when carnitine, found in red meat, is consumed, the bacteria in the human digestive tract can change the compound into TMAO, which leads to the clogging of the arteries.

The researchers looked at the levels of these two factors in 2,595 patients, composed on omnivores, vegans and vegetarians. The patients all chose to have cardiac evaluations. On top of this data set, the team also looked into the effects of a high-carnitine level diet in mice. The researchers concluded that higher levels of carnitine and TMAO increased a patient's risk for heart diseases, strokes, heart attack, and even death. The researchers also noted a huge difference between how vegans and vegetarians metabolize carnitine in comparison to omnivores. They found that vegans and vegetarians who were given high levels of carnitine did not necessarily produce high levels of TMAO, which did not increase their risks for cardiovascular diseases. Omnivores, on the other hand, had the same high levels of TMAO when they consumed high levels of carnitine.

"The bacteria living in our digestive tracts are dictated by our long-term dietary patterns," Hazen said. Hazen is the Vice Chair of Translational Research for the Lerner Research Institute and section head of Preventive Cardiology & Rehabilitation in the Miller Family Heart and Vascular Institute at the Clinic. "A diet high in carnitine actually shifts our gut microbe composition to those that like carnitine, making meat eaters even more susceptible to forming TMAO and its artery-clogging effects. Meanwhile, vegans and vegetarians have a significantly reduced capacity to synthesize TMAO from carnitine, which may explain the cardiovascular health benefits of these diets."
Carnitine is not a necessary nutrient, and since red meat has been proven to be detrimental for health numerous times, the researchers suggest that people should limit their intake of the product. Furthermore, carnitine is not only found in red meat, which includes beef, lamb, venison, mutton, duck, and pork, and oftentimes in energy drinks.

The study was published in Nature Medicine.