"To further make the case, researchers checked the levels of l-carnitine in the blood of
nearly 2,600 people who were having elective heart check-ups.
By itself, the nutrient didn’t seem to make a difference. However, people who had
high levels of both l-carnitine and TMAO were prime targets for heart disease,
further evidence that it’s the bacterial alchemy — not the l-carnitine alone — that poses the real threat.
Finally, the researchers found that feeding l-carnitine to mice doubled the animals' risk
of developing arterial plaques, but only when the mice had their usual gut bacteria.
When the animals were treated with gut-clearing antibiotics, l-carnitine in the diet did not encourage plaques.
Daniel Rader, director of preventive cardiovascular medicine at the University of Pennsylvania,
says that the study makes a “fairly compelling” case that intestinal bacteria
feeding onl-carnitine increase the risk of heart disease"
http://www.scientificamerican.com/article.cfm?id=red-meat-clogs-arteries-bacteria