Gut bacteria convert dietary L-carnitine to TMAO, thus leading to what the new scientific research has discovered to be causing stroke, heart damage and death. 
It is said that; foods containing L-carnitine can be the reason why gut bacteria becomes available in the human body.
Gut bacteria covert carnitine to TMAO. Medical research has proven that TMAO is the number one causer of Cardiovascular diseases.

Vegans appear to lack the gut bacteria that convert carnitine to TMAO.