But when a vegan ate the same combination, he showed no increase in TMAO or bacterial change.

WSJ: New Health Culprit Carnitine Found in Red Meat

But when a vegan voluntarily ate the same combination, he showed no increase in TMAO or bacterial change.

WSJ: New Health Culprit Carnitine Found in Red Meat

In the study, when longtime meat-eaters consumed an eight-ounce steak and a carnitine supplement, their bacteria and TMAO levels rose considerably.

WSJ: New Health Culprit Carnitine Found in Red Meat

"In the future, maybe there will be a heart-healthy yogurt, or a drug to block the formation of TMAO, " he said.

WSJ: New Health Culprit Carnitine Found in Red Meat

"Cholesterol is still needed to clog the arteries, but TMAO changes how cholesterol is metabolized like the dimmer on a light switch, " he said.

WSJ: New Health Culprit Carnitine Found in Red Meat

In the study, when a longtime omnivore consumed an eight-ounce steak and a carnitine supplement, both his bacteria and TMAO levels rose considerably.

WSJ: New Health Culprit Carnitine Found in Red Meat

The study, sponsored by the National Institutes of Health, didn't assess how little red meat people could consume and still have elevated TMAO.

WSJ: New Health Culprit Carnitine Found in Red Meat

One surprising finding, Dr. Hazen said, was how long-term dietary patterns affected the amount of TMAO-producing bacteria in the gut and thus magnified the risk.

WSJ: New Health Culprit Carnitine Found in Red Meat

One surprising finding, Dr. Hazen said, was how a long-term diet that includes meat affected the amount of TMAO-producing bacteria in the gut and thus magnified the risk.

WSJ: New Health Culprit Carnitine Found in Red Meat