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Steak, Bacteria, and Heart Disease

A link between eating red meat and heart disease has been known for a while, but just how eating a steak leads to atherosclerosis isn't quite clear, writes The Economist. Stanley Hazen from the Cleveland Clinic, though, says the effect might be mediated through the gut microbiome.

As they report in Nature Medicine, Hazen and his team found that intestinal microbes metabolize L-carnitine, a trimethylamine found in red meat, to trimethylamine-N-oxide, which, in mice, leads to atherosclerosis. Trimethylamine-N-oxide levels, they added, were higher in human omnivores than in human vegetarians or vegans.

The necessary microbes, The Economist notes, are not always present — vegetarians and vegans are less likely to be able to produce trimethylamine-N-oxide, even after taking carnitine supplements or when persuaded "in the interests of science" to eat a steak. And when antibiotics are used to kill off gut bacteria, even steak eaters produce less trimethylamine-N-oxide.

In a cohort of nearly 2,600 people, plasma levels of it and its L-carnitine precursor were associated with increased risk for cardiovascular disease and cardiac events like heart attack or stroke. And in mouse studies, the researchers found that prolonged exposure to L-carnitine led mice to develop atherosclerosis.

While "the precise chain of events linking microbes to heart disease is still unclear," The Economist adds that "this study suggests that people looking for the link between heart disease and the eating of meat have been ignoring two culprits, carnitine and bacteria."

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