While its role in the body should be to transport fatty acids into cells to be used as energy, the study – published in the journal Nature Medicine – shows that certain bacteria in the digestive tract actually convert the compound to TMAO, a metabolite that promotes thickening of the arteries.
Carnitine – also known as l-carnitine and vitamin Bt – is found in some energy drinks and is sold as a dietary supplement. It is “generally regarded as safe”, according to the US Food and Drug Administration.
Researchers at Lerner Research Institute of the Cleveland Clinic looked at the TMAO levels of vegetarians, vegans and omnivores, and also recorded those of 2,595 heart patients.
“Cholesterol is still needed to clog the arteries, but TMAO changes how cholesterol is metabolised, like the dimmer on a light switch,” said lead researcher Dr Stanley Hazen. “It may explain why two people can have [the same cholesterol levels] but one develops cardiovascular disease and the other doesn’t.”
The study also shows that the longer people have been eating meat, the higher the levels of TMAO-producing bacteria. A vegan test subject given a carnitine supplement showed no increase in TMAO or bacterial change, according to Dr Hazen. “Vegans basically lose their ability to digest carnitine,” he said.