Rarely studied chemical holds answers for relationship between red meat consumption and heart disease

Source: Nature Medicine, The New York Times

A series of recent studies illuminate the importance of a rarely studied chemical on heart disease risk, reinforcing the relationship between red meat consumption and heart disease risk but challenging the long-held belief that this is primarily the result of saturated fat and cholesterol. This chemical is "burped" out by intestinal bacteria after people eat red meat. The liver quickly converts it to another rarely studied chemical TMAO, which enters the blood and increases heart disease risks.

An earlier study identified the substance carnitine, often found in red meat, as an unsuspected culprit in heart attacks. The carnitine was not dangerous itself; instead, the danger presented itself when intestinal bacteria metabolized it, transforming it into TMAO released into the blood.

A second study, which asked participants to eat a steak, found that a meat-eater's TMAO levels soared a few hours after eating a steak. When a vegan ate a steak, however, almost no TMAO appeared in the blood. When the meat eaters were given a dose of antibiotics to wipe out their gut bacteria, researchers found that they no longer had TMAO in their blood before or after consuming the meat, suggesting that the issue was truly a result of gut bacteria.

Later blood analyses found that TMAO levels were correlated with higher heart disease risk, independently of smoking, high cholesterol and blood pressure. Researchers theorize that TMAO allows cholesterol to enter artery walls and prevents the body from excreting excess cholesterol. These studies also call into question the safety of consuming carnitne in other forms, including energy drinks and body building supplements.