Scientists may have figured out why too much red meat is bad for the heart.

It is already known that people who eat a lot of red meat are at an increased risk of developing heart disease. However the saturated fat and cholesterol content of red meat is not enough to fully explain this risk.

This discrepancy has been put down to a number of things, including genetics and the cooking process.

However, US scientists have discovered that a compound that is abundant in red meat - known as carnitine - promotes atherosclerosis (hardening of the arteries).

Their study included data from over 2,500 patients, as well as tests on mice. They found that bacteria which live in the human digestive tract metobolise carnitine, turning it into TMAO, a chemical substance which appears to promote atherosclerosis.

The study found that overall, patients with higher levels of carnitine and TMAO in their bodies had an increased risk of developing heart disease and suffering major heart events, such as heart attacks and stroke.

Not surprisingly, the study also found that TMAO levels tended to be much lower in vegetarians and vegans, compared to meat eaters.

Carnitine occurs naturally in red meats such as beef, lamb, pork and venison. It is also a common ingredient in energy drinks and can be taken as a supplement.

"Carnitine is not an essential nutrient. Our body naturally produces all we need. 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," the team from Cleveland said.

Details of these findings are published in the journal, Nature Medicine.

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