WASHINGTON — Scientists may have uncovered another culprit in red meat, besides saturated fats and cholesterol that clog arteries contributing to heart disease - a chemical called carnitine. Researchers have found tantalizing evidence that bacteria inside the body convert carnitine into a compound that hardens arteries, contributing to arteriosclerosis and increasing the risk of heart attack.
For years, doctors have recommended that patients limit their consumption of red meat, including steak and lamb, because it’s felt the marbled fat and cholesterol in the meat is a major contributor to cardiovascular disease, marked by the production of artery-clogging plaques that can lead to heart attack and stroke.
But experts say a diet rich in red meat is not the only risk factor for heart disease. For example, not all individuals with high blood pressure and elevated cholesterol who eat a lot of steak, setting them up for heart disease, develop clogged arteries.
Now, researchers at the Cleveland Clinic in Ohio have identified a chemical called carnitine that, when metabolized by gut microbes, produces a substance called TMAO - found to be elevated in red meat eaters, increasing their risk of heart disease.
“The notion that there’s something more to red meat than just saturated fats has been banging around for a long while," said Stuart Seides,s chief of the MedStar Heart Institute in Washington. "This is the first scientific link that may explain at least part of that association.”
Cleveland Clinic researchers studied more than 2,500 people, measuring their blood levels of carnitine after they ate a steak, as well as levels of the chemical byproduct TMAO.
For the study, steaks were also consumed by vegetarians and vegans who eat no animal products, including eggs and cheese. Investigators found that the red meat eaters had the highest levels of TMAO compared to the non-meat eaters who had little or no TMAO in their systems.
Because vegetarians and vegans don't, as a rule, eat meat, it's thought the microbes in their guts couldn’t process the carnitine, turning it into TMAO.
In addition, researchers studied the substance in mice, finding that rodents fed diets high in TMAO developed hardening of the arteries. But when scientists suppressed the gut bacteria, the heart disease process was reversed.
The MedStar Heart Institute’s Seides says it may someday be possible to limit cardiovascular disease using antibiotics to kill certain, still unidentified gut bacteria, to keep them from transforming carnitine into heart-disease causing TMAO.
“So that even if you eat meat, the carnitine doesn’t get converted into what is believed to be the offending agent. So, much to learn and this is a very interesting and provocative study, and just peels back the onion a little bit on this very complex question of coronary heart disease,” he added.
Carnitine is found in smaller quantities in fish and poultry and in some vegetables and wheat, and some people take it as a supplement. But beyond red meats which should be limited for other reasons, Seides says it’s too soon to recommend that people stop consuming foods containing carnitine.
An article on the link between the chemical carnitine, TMAO and heart disease is published in the journal Nature Medicine.