In their study published in the journal Nature Medicine, researchers examined a nutrient called “carnitine,” which our bodies produce naturally to help with energy metabolism. (We produce enough carnitine on our own; we don’t need extra from food.) Some intestinal bacteria use carnitine as food, which gives rise to an artery-clogging compound called trimethylamine-N-oxide, or TMAO. “TMAO changes our cholesterol metabolism and contributes to the accumulation of cholesterol within the artery wall,” says Stanley Hazen, MD, PhD, the study’s co-author and vice chair of translational research for the Cleveland Clinic Lerner Research Institute. Dr. Hazen and his team studied blood data from about 2,600 patients undergoing heart evaluations, and the link was clear: “We saw an association between carnitine and risk for heart attack, stroke, and death,” Dr. Hazen says. But that risk seems to be dependent on TMAO levels, which differed depending on the patients’ diets. In another part of the study, researchers examined the blood levels of vegans, vegetarians, and meat-eaters after they ingested a uniform amount of carnitine, whether through a sirloin steak or vegan-friendly supplement. While meat-eaters made significant amounts of TMAO, vegans and vegetarians generated virtually none. “They simply didn’t have the microbes in their intestines to digest it,” Dr. Hazen said. To confirm the results, researchers then gave the meat-eaters a week-long round of antibiotics to suppress bacteria. When they re-administered carnitine, no one produced any TMAO—but after quitting antibiotics for a month, meat-eaters’ guts had repopulated with TMAO. “It was proof that gut microbes played a role in the metabolism of carnitine to produce this artery-clogging compound,” Dr. Hazen says. Antibiotics aren’t a treatment for heart disease—meaning, you can’t pop some pills with your steak to cancel out the carnitine—since microbes develop antibiotic resistance quickly, Dr. Hazen says. But it’s possible to shift your intestinal flora in the heart-healthy direction in just one or two months by adopting a vegetarian or vegan diet, he says. Soon, deciding whether or not your bacteria need a veggie diet will become easier. A TMAO blood test for patient use is slated to hit the market later in the year, Dr. Hazen says. “It will show who’s at increased risk independent of existing risk factors, and it may also help to personalize your diet,” he says. In the meantime, whether it’s because you want to limit saturated fat, cholesterol, or carnitine, limiting your red meat consumption is a good call. Get started with these 5 Easy Vegetarian Recipes.
