Red meat has not exactly been on the A-list of healthy foods for a long time as it’s been linked to an increased risk for cancer and heart disease. New research in the journal Nature Medicine suggests that eating even lean steak that is low in fat and cholesterol can be bad for your heart. The reason is that a chemical found in red meat, trimethylamine-N-oxide (TMAO), can actually “encourage” the growth of fatty deposits on the walls of the arteries.
However, a vegan who was a participant in the study did not show the same spike in levels of TMAO — which changes the very metabolism of cholesterol and slows the removal of it from the arteries’ walls — after eating a 200-gram sirloin steak.
Dr. Stanley Hazen, head of cardiovascular medicine at the Cleveland Clinic in Ohio, and his colleagues made this discovery while conducting a series of experiments to find out why red meat consumptions has been linked to heart disease. They first gave 77 participants (26 of whom were vegans or vegetarians) the nutrient carnitine, which is found in meat and dairy products.
Taking carnitine, which is also taken as a supplement to improve athletic performance and for weight loss and which is found in energy drinks, increased the volunteers’ levels of TMAO. But the vegans and vegetarians produced far less TMAO after taking carnitine supplements. Analysis showed that they indeed had “very different types of bacteria in their guts” than did those who ate meat.
From this, Dr. Hazen concluded that eating meat regularly promotes the growth of intestinal bacteria that then turns the carnitine in red meat into TMAO. The researchers confirmed their findings by checking carnitine levels in people who were having voluntary heart check-ups. Carnitine on its own was not linked to heart disease but, when combined with TMAO, it turned people into “prime targets for heart disease.”
“Bacterial Alchemy” At Work in Our Intestines
It’s not carnitine alone that increases your risk for heart disease, but what Nature.com refers to as “bacterial alchemy.” If you’re regularly eating meat, you are setting in motion a process in which intestinal bacteria feed on the carnitine from a steak, burger, etc. and produce TMAO. Over time, your risk for heart disease rises.
Carnitine is also found in chicken, fish and dairy products, but in far smaller amounts than in red meat. It had not previously been connected to an increased risk of heart disesase, Gina Kolata notes in the New York Times.
As a result of the study, Dr. Hazen — once a routine consumer of red meat — has himself lowered his consumption of it, to once every two weeks. The study also indirectly offers more evidence of why foregoing meat has its pluses. The vegan who ate the sirloin steak in the study was indeed found to have “virtually no TMAO” in his or her blood — a suggestion of why not eating meat can do your heart good (and then some).
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