Cleveland Clinic study links carnitine to heart disease
CLEVELAND – Researchers with the Cleveland Clinic report that a compound found in red meat and energy drinks has been found to promote atherosclerosis, the hardening or clogging of arteries.
The findings were published recent in the journal Nature Medicine. The findings show that bacteria living in the human digestive tract metabolize carnitine — a naturally-occurring compound in red meat —into trimethylamine-N-oxide (TMAO), a metabolite previously linked in a 2011 study to the promotion of atherosclerosis in humans. Additionally, the study shows that a diet high in carnitine promotes the growth of bacteria that metabolize carnitine, compounding the problem.
“The bacteria living in our digestive tracts are dictated by our long-term dietary patterns,” said Dr. Stanley Hazen, lead researcher. “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 naturally occurring in beef, venison, lamb, mutton, duck, pork and other red meats. It is also used as a dietary supplement and a common ingredient in energy drinks.
Betsey Booren, Ph.D., AMI Foundation chief scientist, said in a statement that cardiovascular disease is a complex condition that may have a variety of factors associated with it, including genetics and lifestyle choices. However, attempts to link cardiovascular disease to a single compound found at safe levels in red meat oversimplifies this complex disease, she said.
"In fact, the study’s authors themselves say red meat is not to blame, but rather argue that excessive supplementation with L-carnitine that is found at safe and healthy levels in red meat may be a concern,” Booren said. “It is important to keep in mind that there are many other studies done on L-carnitine that do not show any adverse health effects at a variety of doses. In fact, the National Institutes of Health fact sheet on L-carnitine shows it is safe and essential.”
She added that the full body of research into cardiovascular disease and diet shows that red meat can be enjoyed as part of a healthy, balanced diet.
“Federal nutrition data shows that the protein group is the only food group consumed at proper levels and that Americans, on average, consume the recommended amount of meat,” she said. “This study should not prompt any dietary changes and consumers who enjoy red meat should continue to do so with confidence.”
However, Dr. Hazen said that the new findings suggest a new link between red meat consumption and cardiovascular disease because although many studies claim to show that a diet with frequent red meat consumption is associated with increased cardiovascular disease risk, the cholesterol and saturated fat content in red meat does explain increased risks.
Hazen cautioned that more research needs to be done on the safety of chronic carnitine supplementation.
“Carnitine is not an essential nutrient; our body naturally produces all we need,” he said. “We need to examine the safety of chronically consuming carnitine supplements as we’ve shown that, under some conditions, it can foster the growth of bacteria that produce TMAO and potentially clog arteries.”