Steak Linked to Heart Disease

Gut bacteria digest L-carnitine, a nutrient found in red meat, and produce a heart-harming molecule as a result.

By | April 10, 2013

WIKIMEDIA, _BuBBy_ Studies have found associations between red meat and heart disease, but exactly why the popular foodstuff can be harmful has been unexplained. A new study published earlier this week (April 7) in Nature Medicine suggests that a molecule found in steaks called L-carnitine is at fault. Gut bacteria convert it into trimethylamine N-oxide (TMAO), a molecule linked with arterial clogging, ScienceNOW reported.

The researchers found that after eating steak, human research subjects had elevated levels of TMAO. When some volunteers took antibiotics for a week and then the researchers gave them steak again, subjects’ blood TMAO levels were extremely low. Finally, feeding mice L-carnitine supplements, the researchers found that the animals’ TMAO levels soared, and their atherosclerosis levels doubled, but only if they had their full complement of gut bacteria.

The more L-carnitine the mice and humans were used to ingesting, the more TMAO they produced in response to the same quantity of food, indicating that their gut microbiota compositions were adapting to the presence of L-carnitine. When the researchers gave vegetarians and vegans L-carnitine supplements, they produced little TMAO.

Stanley Hazen, a cardiologist at the Cleveland Clinic and an author of the study, told Nature that understanding how bacteria digest the food we eat could be important for understanding many dietary health effects. “Bacteria make a whole slew of molecules from food, and those molecules can have a huge effect on our metabolic processes,” he said.

Hazen warned against taking products supplemented with L-carnitine, which can be found in energy drinks and body building supplements, saying that benefits were unproven. “I see no reason why anyone needs to take it,” he said.

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